uzet cu si slobodu i ovamo kopirat postove koji su postani na temi o HE a koji se odnose na savladavanje nekih lekcija ne vezano uz skolu
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naucimo sami :)
uzet cu si slobodu i ovamo kopirat postove koji su postani na temi o HE a koji se odnose na savladavanje nekih lekcija ne vezano uz skolu
Ancica prvotno napisa
ja znam samo da se dodavanjem soli povecava vreliste vodi
Molim te, objasni ovo.
hm, na osnovu ovog mogu si nekak objasniti spomenuti fenomen. hvalaja znam samo da se dodavanjem soli povecava vreliste vodi
a sad, zasto sol povecava vreliste vodi?
postala ja pitanje jednom prijatelju fizicaru 8)a sad, zasto sol povecava vreliste vodi?ja znam samo da se dodavanjem soli povecava vreliste vodi
razmisljala sam malo i sama o tome, ali nisam daleko stigla. dakle, temperatura Ancicine zobene kase definirana je brzinom gibanja (kinetickom energijom) molekula u njoj. ako se u nju uspe malo soli povecat ce se broj molekula, pa ce trebati u sustav uvesti vise topline da se postigne odredena brzina kretanja svih njih. ali ne vidim kako bi se to dovelo u vezu s povisenjem vrelista. mozda je odgovor ipak vise kemijske nego fizikalne prirode? :/
Marija 71, u poomoooc!!
a kad smo vec kod soli, zanimljivo je spomenuti da njezin dodatak takoder smanjuje lediste! zato zimi posipamo ceste solju...
ajme kako ću se sad osramotiti......
evo ja mislim da je potrebno uložiti više energije u isparavanje smjese vode i soli nego u isparavanje čiste vode
Re: naucimo sami :)
litala super ideja :Duzet cu si slobodu i ovamo kopirat postove koji su postani na temi o HE a koji se odnose na savladavanje nekih lekcija ne vezano uz skolu
ja na svim stručnim skupovima koje ja organiziram preferiram "fiziku iz naftalina " tj da ostalim učiteljima prezentiram te male kućne pokuse koje djeca uz minimalan angažman roditelja mogu ponoviti i doma
Molim objašnjenje pojme HE djeca...(:? )
he - home education.
al za daljnju raspravu o tome - molim pogledaj topic na ovom podforumu
a zasto ?evo ja mislim da je potrebno uložiti više energije u isparavanje smjese vode i soli nego u isparavanje čiste vode
je li moguce da je to zbog nekakvih privlacnih sila izmedu molekula vode i iona Na+ i Cl-, koje onda cine da je potrebna visa temperatura da bi se molekule vode"otele" i pretvorile u paru? keeemicarii
a lediste - zasto se lediste snizava dodatkom soli?
Evo ovako. Do vrenja općenito dolazi kad se tlak para koje se nalaze iznad otapala, u ovom slučaju vode, izjednači s vanjskim tlakom. Zato će npr. juha zakipiti ranije ako ima poklopac, nego bez njega.
Kod tekućina postoji ravoteža između molekula koje se nalaze u tekućem stanju i kod molekula koje se nalaze u plinovitom stanju - to je para iznad otapala. Ravnoteža znači da se neprestano odvija isparavanje molekula vode, ili nekog drugog oatpala s površine, i ponovna kondenzacija.
Ako je u vodi nešto otopljeno, npr. sol, onda je u loncu udio molekula vode manji od 1 (odnosno manji od 100%, u loncu se ne nalaze samo molekule H2O, nego i NaCl). Što je više molekula neke otopljene tvari prisutno, manja je vjerojatnost izlaženja molekule otapala u paru, i ta je vjerojatnost toliko puta manja koliki je molni udio (odnosi se na količinu, brojnost molekula) tvari koja je otopljena.
E sad, ako manje molekula vode izlazi van, odnosno isparava, potrebna je veća energija (ko što točno napisa moja imenjakinja
To npr. vide ljubiteljice turske kave, kad kuhate kavu, voda zavrije, dodate šećer, pa vrenje stane.
Što se tiče ledišta, do skrućivanja dolazi u trenutku kad se izjednači tlak pare iznad krutine, odnosno leda, i iznad čiste vode. S obzirom da je iznad otopine tlak pare niži, izjednačavanje tlaka će se dogoditi na nižoj temperaturi, to se zapravo puno ljepše vidi grafički, nego ovako opisno. I to se koristi zimi kad se posipava led - voda iznad leda otapa sol, snizi se tlak pare iznad tekuće vode, a tlak pare iznad leda je viši, pa se led otapa.
E da, to se zove Raoultov zakon
Marija
Jos samo dva pitanja:
Znaci li to da se vreliste mijenja s promjenom atmosferskog tlaka? Hoce li juha prije zakipiti na visoj nadmorskoj visini?Do vrenja općenito dolazi kad se tlak para koje se nalaze iznad otapala, u ovom slučaju vode, izjednači s vanjskim tlakom.
Ovo radi samo na temperaturama oko nule (i malo nizim)? Ako imamo temp. od -20, nema sloja vode iznad leda u kojem bi se otopila sol, pa nista od svega toga?I to se koristi zimi kad se posipava led - voda iznad leda otapa sol, snizi se tlak pare iznad tekuće vode, a tlak pare iznad leda je viši, pa se led otapa
Hvala
kanga, kanga.
Jos jednom cemo konstatirati da razlicitim ljudima odgovaraju razliciti nacini ucenja. Eto, ja to nisam (dovoljno dobro) naucila u skoli, ali plodove ovog tecaja koji su mi odrzale Maria71kanga, kanga.i Marija
i opet dolazimo do onog bez emocije nema učenja
Kanga zgodan je pokus sa ledom i koncem preko komada leda ,a na kraje konca su stavljeni utezi ( od 1 ili 2 kg )
na sobnoj temperaturi led se neće otopiti za 5 min, ali će konac s utezima proći kroz njega prije nego se sam blok leda otopi- regelacija leda
povećan tlak, led se otapa pod koncem a iznad se opet smrzava
al bi podučavala druge
jedna od laboratorijskih vježbi koje je moja seka radila sa svojim srednjoškolcima je bilo praviti raznorazne parfeme i kreme. djeca su bila oduševljena, posebice što su napravljeno smijeli odnijeti doma i koristiti.dolazimo do onog bez emocije nema učenja
wow! cool 8)
mc, fiziku ce mi djecu poducavati Marija71
joj, krivi sam zadnji smajlic stavila - trebao je biti ovaj
vrlo rado
najnoviji ternd poučavanja fizike je da se krene što ranije, i u vrtićkoj dobi
eksperimentiram na marku
dream on
da ne velim da je maria dio tog sistema, učila kako se podučava u sistemu, plaća ju sistem... na finjaka vas pokušava sve ukalupiti... brrrrrrr :/
emso
što sad ispadoh
borgova matica
kužite... kako pokušava sve okrenuti na šalu, sad kad sam je otkrila... 8) be afraid.... be very afraid.... možda između E=mc2 vašoj djeci uvali još koje ćirilično slovo... :/
ali neee mc, nece ih poducavat u ucionici
za cirilicu cu se pobrinuti ja, to mogu
mc
evo uspjela si me nasmijati nakon što me šokirao ofucani i ostarjeli Johnny Logan...............
možeš izvući učitelja iz učionice, al nikad učionicu iz učitelja 8) ona je i sama već u kalupu... sve ove godine dok se školovala i sad dok podučava druge... teško je to... brainwashing... indoktrinacija... ocjenivanje.... prozivanje.... testovi.... brrrrr.... vidi http://www.coolinarika.com/repository_images/image_raw/18843/content_large/]marijin kalup[/url]ali neee mc, nece ih poducavat u ucionici
samo se vi smijte.... a kasnije će biti: kuku lele, emso, što uradismo!
nego, kako stoji s plaćanjem ?
maria, nije valjda na dori ?
p.s. i televizor ima :/ :/
Ajmo na temu
kako napraviti priručni elektroskop?
plastična flaša ,čavao ,i komadić alu folije
probušiti plastični čep borerom i stavit čavao da viri iz čepa
na čavao koji bi bilo dobro malo savinuti na kraju staviti 2 tanke trake staniola
sve smontirati
uzeti češalj i vunenu krpu ,natrljati češalj i primaknuti ga priručnom elektroskopu tj glavici čavla koji viri iz čepa
alu folija će se razdvojiti i onda priča što se dešava itd.....
[quote="mama courage"] http://www.coolinarika.com/repository_images/image_raw/18843/content_large/]marijin kalup[/url]
Sto se tice ostalog, gle - ja ti volim u ljudima gledati ono sto mi se svida i fokusirati paznju na ono sto mi predstavlja zadovoljstvo. Ne vjerujem u postojanje apsolutne istine u ovom nasem relativnom svijetu. Ali vjerujem u lokalne maksimume i njima tezim. Trenutno pronalazim veliko zadovoljstvo u cinjenici da Marija71 umije zanimljivo pricati o temama iz fizike. Ako imas za ponuditi nesto afirmativno ili saljivo - samo naprijed! Sve ostalo ti je u mom slucaju cisti gubitak vremena. Jednostavno nisam prijemljiva.
Evo jos malo o utjecaju soli na povisenje vrelista:
http://www.physlink.com/Education/AskExperts/ae643.cfm
da nam bude sve na jednom mjestu, ima par topika sa slicnim temama:
http://www.roda.hr/rodaphpBB2/viewto...+fizika+pokusi
http://www.roda.hr/rodaphpBB2/viewto...+fizika+pokusi
Ej Zoila, hvala!
Ja bih rado postala jedan link za roditelje i djecu
koje zanima sto se i kako dogada u nasem mozgu:
http://faculty.washington.edu/chudler/neurok.html
Ako ima pitanja, tu sam!
eksperimenti iz kuhinje Roberta Krampfa...
prvi, pandan ultrazvuku u trudnoci
This Week's Experiment - #463 Eggs-ray Vision
This week's experiment came from trying to hatch some eggs. We are using an incubator, and hoping to hatch some chicks and ducks. This week, we candled the eggs, to see if they were developing. Candling is a technique for looking inside an egg, without breaking the shell. To try this, you will need:
an egg
a bright llight
a cardboard box
a dark room
a small bowl or dish
First, cut a hole about the size of a quarter in the bottom of the cardboard box. Turn the box upside down, and put the bright light inside. Position the light so that it is shining up through the hole. Then darken the room and place the egg over the hold. The light should shine into the egg, making it glow.
Look carefully at the egg. If you were looking at a fertile egg that had been incubated for a couple of weeks, you would see a large, dark mass. That would be the baby chick.
While you won't see that in your egg, you can see a few things. First, you can see the air cell. It will look like a small bubble at the large end of the egg, and that is exactly what it is. In a fresh egg, it is small, but if you keep the egg in the refrigerator for a while, it loses part of its water and the air cell gets bigger.
You may also see lots of tiny light spots in the shell. Those are pores that let the egg breath. It lets oxygen get in, and lets carbon dioxide and water get out.
If you have a very bright light, you may see just a hint of the yolk. That is about all that you should see by candling, but by breaking the egg, we can learn even more about the inside. Carefully crack the egg into a small bowl or dish. Try not to break the yolk.
Look carefully at the inside of the shell. Along the inside of the hard shell, you should see a thin, skin-like membrane. Actually, there are two membranes, one inside the other. If you look at the inside of the large end of the egg, you should see the air cell, in between the two membranes. These membranes control what goes in and out of the egg, keeping it from drying out, and helping to keep out microorganisms that would spoil the egg.
Next, look at the egg. Most people are familiar with the white or albumen (which comes from albus, which is latin for .... you guessed it. White.) Inside the albumin is the yolk. Many people think that the yolk develops into the chick, but it does not. Instead, the yolk is a stored food supply to feed the chick until it hatches. Even if you have a fertilized egg, the part that will develop into the chick is VERY tiny, so don't expect to see it.
In the albumin, you may also see one or two small, white structures. Again, many people think that this is the start of the chick. Instead, these are chalazae, rope-like structures that hold the yolk in the center of the albumin. By keeping it away from the shell, they protect the yolk from contamination by any microorganizms that find their way into the egg. That is also why you should store eggs with the large end up. Since the air cell is an air bubble, it tries to float upwards. If the large end of the egg is down, the air cell stretches upwards, bringing it closer to the yolk, which could cause the egg go bad quicker.
Now that you have dissected the egg, the only thing left to do is to denature its proteins. To do that, put a little butter into a skillet. Turn the heat on medium and place the egg into the skillet. The heat will change the protein of the egg, causing the albumin to change from a clear gel to a firm, white solid. The yolk will also take on a firm texture. Then add a little salt and pepper and you have a very nice snack.
Have a wonder filled week.
This Week's Experiment - #464 Oil and Water and Static, Oh My!
This week's experiment is one that I came across while researching for the science videos. I came across an article that compared the effect of static fields on polar and nonpolar materials. Sound complicated? Really, it is simple and amazing. To try this, you will need:
a balloon
water
oil
syrup
We will start with something that we have done before. Blow up a balloon and tie it off. Then rub it against your hair or a piece of cloth, to build up a static charge. If you bring the balloon near the back of your hand, you should feel the hair standing up on your hand.
Then turn on the water in your sink. Turn the water down to form a very thin stream of water. Bring the balloon near the stream of water, and you should see that it bends towards the balloon. You may even see drops leap from the stream to the balloon.
Now come the new part. We want to try the same thing with a thin stream of oil. I put a bowl in the sink and then poured cooking oil into it, trying to get a nice, thin stream like I had with the water. This time, when I brought the balloon near the stream, it did not bend or react to the static charge. Why?
Well, the article that I read said that it was because water is polar and oil is nonpolar. What in the world does that mean? No, it doesn't mean that you don't find oil at the North Pole. If a molecule is polar, then one part of the molecule will have a positive charge and another part will have a negative charge. Nonpolar molecules have a neutral charge all over. That should mean that the polar molecules will be pushed or pulled by the electrostatic charge on our balloon.
OK, so it seemed to work, but I was wondering if part of this was because the oil was thicker than the water. To test that, I did the experiment again, using some sorghum molasses (a thick syrup popular in the Southern United States). Since it is water based, it is also a polar liquid. Instead of pouring it into the sink, I poured a thin stream onto some nicely buttered toast. The charge of the balloon did the same thing to the syrup that it did for the water, showing me that even thick liquids are bent by the static charge. It also made a nice, tasty design on my toast.
That lead me to wondering if the same thing applied to solids. Wax is a nonpolar solid, while wood is polar. If solids react in the same way as liquids, then you should be able to sort a pile of tiny bits of wax and wood by bringing the balloon near the pile. Does it work? <grin> Guess you'll have to try it to see. Why should I have all the fun?
Have a wonder filled week.
This Week's Experiment - #467 Towels
The idea for this week's experiment came from a water leak. We woke up to a lot of water and wet floors. The clean up gave me plenty of time to think about how a towel works, and why it soaks up water. To explore this, you will need:
a glass of water or your favorite drink
2 soda straws
Thin straw or coffee stirrer
a paper towel
Fill the glass with some tasty liquid and put one of the straws into it. Before you take a drink, look closely at the straw. Even if the straw is not clear, you should be able to see that the liquid has risen slightly up into the straw.
This is called capillary action. Water is very sticky stuff. When it comes in contact with the straw, the water molecules stick to the plastic. They are attracted so strongly that the water climbs slightly up the surface. How high the water will climb is controlled by several things.
First, it is controlled by the material. There are some substances, such as oil and wax, that water does not stick to, so the water will not climb up their surface. A towel made of wax would not work very well.
Second, to do much climbing, the water needs a small space. Notice that the water climbs the inside of the straw, but does not go nearly as high on the outside. Is the outside of the straw made of something different? No. Put the second straw into the glass, beside the first straw. Place the straws side by side, and then move them very slightly apart. You should see that the water has now climbed up between the two straws. Why?
On the outside of the straw, the water is only sticking on one side, the side towards the straw. All the water on the side away from the straw is being held up by the attraction on the other side. The water will climb until the attraction of the water to the plastic is balanced by the downwards pull of gravity. With the two straws, you have water sticking to the plastic on two sides. Twice as much support holds up twice as much weight, which lets the water climb higher. Inside the straw, the water is surrounded, sticking on all sides, so it climbs even higher.
Is there a way to make the water climb even higher? Yes. You could make the straw smaller. If you can find a very thin straw, or one of the straw-like coffee stirrers that they give at fast food places, compare a thin straw with a thick one. You will see that the thinner the straw is, the higher the water will rise. Why does the water climb higher in a thin straw? The water in the center is being supported by sticking to the water that is sticking to the plastic. A smaller straw means that there is less water in the middle to be supported, so the water can climb higher.
So for a towel to work well, it needs to be made from a substance that water sticks to very well. It also needs to have lots of tiny spaces for the water to climb into. The fibers in the threads of the towel serve that purpose.
Now, think back to the straws. Which do you think would support more water, one large straw or two small ones? Right. Two small straws would have more surface area for the water to stick to, so they would support more water. A towel that has many, very thin threads would work better than one with fewer, thicker threads. That is the idea behind the new, microfiber towels. Lots of very small fibers work very well at soaking up lots of water.
Now, you can finish your drink and think about how towels work, without the need for a major water leak to get you started.
Have a wonder filled week.
This Week's Experiment - #468 Foam
It has been far too long since I did an experiment with ice cream, so I thought this week would be a good time to correct that. We are going to investigate foam. For this, you will need:
a bottle of water
carbonated soda
ice cream
OK, to begin with, what is a foam? According to the Wikipedia, "a foam is a substance that is formed by trapping many gas bubbles in a liquid or solid." OK that should be easy enough. We just need a lot of bubbles. Pick up the bottle of water. Be sure that the lid is on tightly and then give it a good, hard shake. While you are shaking, you should be able to see that there are quite a few bubbles of air in the water. Now, stop shaking the bottle. Instantly, the bubbles disappear. Pure water is not good at keeping bubbles. Its surface tension, that "stickiness" that we looked at last time, gets in the way and causes the bubbles to collapse. What we need is something added that can stabilize the surface of the bubbles. We could use soap, which does a very good job of disrupting the surface tension and makes very good bubbles, but soap does not taste very good.
Pour some soda into a glass. Now we have some foam! Dissolved substance in the soda help to stabilize the bubbles, making them last longer. Still, after sitting for a minute or so, most if not all the foam will be gone. If we want the foam to hang around longer, we need to add some chemicals to make it stronger, and I know just where to find them.
Add a scoop of ice cream to a glass and pour some soda over it. This time, we get even more foam, and the foam lasts much longer. Ice cream is already a foam, with as much as half of its volume made up of air bubbles. To keep these bubbles in place as the ice cream freezes, they add proteins, such as eggs and cream, which can both be w(kršitelj koda)ed into a very nice foam. These proteins make the bubbles in the ice cream stronger, letting the manufacturer add more air. This makes the ice cream lighter in texture. It also makes the end product cheaper to make, since as much as half of what they are selling you is air.
As you pour the soda over the ice cream, some of the proteins mix with the soda, making the foam last much longer. How much longer? I don't know. I always find myself eating the experiment before I can find out.
Have a wonder filled week.
This Week's Experiment - #469 More Foam...and Less
This week's experiment comes from Kaitlin, Cody and Jenna Russell. They wrote to tell me that they made a very interesting discovery about how the order that you add ingredients makes a big difference. To try this, you will need:
carbonated soda
ice cream
two glasses
Lets start by recreating their experiment. Does it make a difference which ingredient you add first? Put a scoop of ice cream into one glass. Pour some carbonated soda into the other. Now, lets compare the difference. Add some soda to the glass with the ice cream. Try to add the same amount of soda that you put into the other glass. Watch carefully, to see what happens and how much foam you get.
Next, add a scoop of ice cream to the glass with the soda. Again, watch carefully. This glass has quite a bit less foam. Why?
In the glass where you added the soda first, the soda produced foam all by itself. If you watched carefully, all this foam vanished when you added the ice cream. Even a tiny bit of ice cream added to the soda will cause all the foam to go away. The proteins from the ice cream change the surface tension, so they actually destabilize the old bubbles as they stabilize the new ones. Part of our foam is going away as the rest is forming.
Adding the ice cream causes the carbonation to leave the soda very quickly. Once you have some ice cream mixed in with the soda, you will notice that it is totally "flat," with no carbonation left. If part of that carbonation has already come out before the ice cream was added, there will be less gas left to form bubbles, so you will get less foam. If you totaled all the bubbles, both before and after the ice cream, you would get the same amount as if you had added the ice cream first. Now that you know what to watch for, you will probably want to do the experiment again, after you finish eating the first one.
Have a wonder filled week!
This Week's Experiment - #477
This week's experiment is one that you have probably seen a thousand times, but you might never have noticed what you were really seeing. To try it, you will need:
a glass of water
detergent
a straw
Fill the glass about half-full of water. Add a drop of dish washing detergent, and stir with the straw. Then blow gently through the straw to blow some bubbles. Hold the glass near a light and notice the colors in the bubbles.
OK, the bubbles have a rainbow of colors. You have probably seen them many times before. Now look carefully at the colors. Then think about the last time you saw a rainbow. Do you remember the colors of a rainbow in order? Do you remember Roy G. Biv? That is the way most people remember the colors of the rainbow. Red, orange, yellow, green, blue, indigo and violet. The physics of a rainbow dictates that the colors will always be in that order.
Now, take another look at the colors of the soap bubbles. The colors are different, and they are in the wrong order. In the bubbles, the colors are yellow, magenta, blue and blue-green. Why are they different?
It has to do with the way the colors are formed. With a rainbow, the colors are caused by separating the different wavelengths. Each color is made up of light waves of the same length. The red you see is made up of light waves in the red wavelengths. The colors are also in order, from the longest visible wavelength, red, to the shortest visible wavelength, violet.
In the soap bubbles, the colors are formed in a different way. Here, the colors are produced by removing colors, not separating them. When light hits the surface of the bubble, part of it is reflected and part of it passes into the liquid. When it hits the inside surface of the liquid, again, part of it is reflected back and part passes on through.
Here is where it gets interesting. The light that reflects back from the bubble's surface mixed with the light that reflects back from the inner surface. Because of the thickness of the bubble, the waves of light are out of step with each other.
Whether we are talking about light or water, waves act the same way when they meet. Think about waves in water. You have the high part of the wave, called the crest. You also have the low part of the wave, called the trough. If two crests meet, they combine to make one very high wave. If two troughs meet, they combine to make a very deep trough. If a crest and a trough meet, they cancel each other out, and you get no wave.
Now, lets go back to our bubble. If the bubble is the right thickness, the red waves of light will be just enough out of step so that they will cancel out the red light. The other colors have a different wavelength, so they are not canceled. If you remove the red light, you are left with a blue-green color. If the bubble is a little thinner, then you will cancel out the yellow light. That gives you a blue color. A little thinner and you cancel the green. That leaves a color called magenta, a mixture of red and blue light. Even thinner and you cancel the blue, giving a golden yellow color. Make the bubble a little thinner and the cycle starts again, so you get repeating bands of blue-green, blue, magenta and golden yellow.
If you watch the bubble, you will notice that the colors swirl and shift. That is because gravity is pulling the water in the bubble downwards. The bubble gets thinner as it gets older, and the top is thinner than the bottom.
Once you know these colors, you will start to see them other places. You can see them in the "rainbows" that you see in an oil or gasoline film on water. You can also see them in the iridescence of sea shells and insect wings.
I tried thinking of a way to connect this with ice cream, but the only thing I could come up with was eating a bowl of rainbow sherbet. Ahh, the things I do for science.
Have a wonder filled week!
This Week's Experiment - #478 Batteries?
I wrote this week's experiment while I was writing an electricity manual for the Memphis Pink Palace Museum's Suitcase Outreach program. Usually I try to stick to everyday language instead of using technical terms when I write the Experiment of the Week. That gets me quite a few email saying that technically I should use "mass" instead of "weight", "NaCl" instead of salt, and so on. This week, I am going to get technical to help show you some interesting things. To try this, you will need:
pliers
a 9 volt battery
battery powered devices around your house
First, look around at some of the things in your house that run on batteries. What if I told you that some of them really do not run on batteries? It would be true, but only on a technicality.
The first battery was invented by Alessandro Volta, back in the year 1800. He found that by using a disc of zinc and a disc of copper with a piece of cloth soaked in salt water placed between them, he could produce a current of electricity. You might have seen similar experiments where you stick a piece of copper and a piece of zinc into a lemon to produce electricity. Volta found that one cell did not produce much electricity, but by stacking several cells, he could combine their voltage (which is named after Volta). The more cells he stacked, the more voltage he got. That stack of cells was the first battery.
That is where our technicality comes in. Technically, a battery has to have two or more cells. When you look at AA, AAA, C and D "batteries", you find that each of them is really a single cell. That means that if you have a small flashlight that only takes one of these, it runs on a cell, not on a battery. Of course, if your flashlight uses 2 D cells, then you have a battery, since the total is 2 cells.
OK, so I am splitting hairs a bit, but there is a good reason. The most voltage that you can get out of a modern electric cell is 1.5 volts. If you look at the voltage on AA, AAA, C and D cells, you will find that all of them produce 1.5 volts (unless they are rechargeable, which usually only produce 1.2 volts) If you find a "battery" that produces more than 1.5 volts, then it probably really is a battery, containing 2 or more cells.
Now, lets look at our 9 volt battery. Because it produced 9 volts, we can be pretty sure that it actually is a battery. Before we check, lets do some math.
Math! Wait a minute! No one said anything about me having to do math! Well, this is simple math, so I guess it is OK. We are going to calculate how many cells the battery has. Let's start with 1.5 volts for one cell. Adding another cell will add the voltages, so we will have 3 volts. If two cells give us 3 volts then 4 cells should give us 6 volts, and that means that to get 9 volts we would need six cells.
Let's check and see if that is correct. Look at the top of the 9 volt battery. It has two electrical contacts on its top. The sides are metal, and bend inwards to hold the top in place. CAREFULLY use the pliers to bend the metal sides away from the top. Be very careful, as the metal edge may be sharp. When you bend the sides enough, you should be able to remove the top. What do you see inside? 6 small electric cells. They look like AAA cells, but they are even smaller. Our math was correct.
You can do the same thing with other batteries. What about one of the large, square, 6 volt lantern batteries? How many cells would it have? Four, right? Right. If you open one, you will find....four D cells. Most car batteries are 12 volts. How many cells would that be? Do the math, and then look at your car battery. You should be able to see evidence that it has 8 cells, which will total to 12 volts.
So you see, there are times when it helps to use the technical jargon. Now I am off for a bowl of ice cream, which will probably cause me to gain some mass.
Have a wonder filled week!
This Week's Experiment - #479 High Bounce
Be sure to try this science experiment outside! It will save you the work of cleaning up the pieces of broken lamps and shattered windows.
For this experiment you will need:
a basketball or soccer ball
a tennis ball
duct or masking tape
a flat, hard surface, outside
Hold the basket ball about shoulder high in one hand and the tennis ball at the same height with the other. Drop both at the same time. If both are fairly new and fully inflated, they should bounce about the same height. OK, nothing strange about that.
Next, use the tape to make a round, raised collar on the basketball. This is going to help you balance the tennis ball on top of the basketball. It does not have to be fancy. Just a ridge of tape in a circle that will fit the bottom of the tennis ball.
Hold the basketball out at the same height as before, with the tape ring at the top. Place the tennis ball into the tape ring. It should balance there. Now, before you drop it, think about what you expect to happen. Then drop the balls.
Understanding the Science
What happened? The tennis ball bounced VERY high. Why did that happen?
When you were holding the basketball and the tennis ball, they had potential energy, the energy of position. When you released them, that potential energy was changed into the energy of motion. In other words, they fell. When the basketball hit the ground, its momentum compressed it, flattening the bottom. The same thing happened when the tennis ball hit the basketball. Their energy of motion was changed into compressed mechanical energy, much like squeezing a spring.
Then the compressed mechanical energy was changed back into the energy of motion. As the basket ball bounced, it bumped into the tennis. That impact transferred some of the energy of motion from the basketball to the tennis ball. The basketball was left with less energy of motion, so it did not bounce as high as it did the first time. The tennis ball wound up with a lot more energy of motion, so it bounced very high.
What do you think would happen if you reversed the two balls, putting the basketball on the top? How much higher would the extra energy from the tennis ball lift it. What if you used a heavier ball instead of the basketball? Or a ping pong ball on the top? There are all sorts of combinations to try, and you will be surprised how much you learn while you are having fun.
Have a wonder-filled week!
This Weeks Experiment - Heating a Balloon
Taken from the original version of experiment #13, written May 15, 1997.
You can see the video version of this experiment at:
http://www.krampf.com/experiment_vid.html
*WARNING* This experiment uses fire. Be safe, use common sense, and be sure there is an adult in the room, so you have someone to blame if something goes wrong.
This is a variation of an old, Victorian parlor trick, but even after more than 100 years, it is still just as amazing. In Victorian times, the experiment was done by folding a calling card (much like a modern business card) into a square container. When the paper container was filled with water, it could be held over a candle to boil the water without the paper catching fire.
For this modern version, you will need:
a candle
matches or a lighter
several balloons
water
Blow up one of the balloons and tie it off. Light the candle. Now, what do you think would happen if you held the balloon in the candle flame? Lets try it and see. Carefully, hold the balloon just at the top of the candle flame. BANG! Just as you probably predicted, the balloon pops and it blows out the candle.
Now, lets try that again, but this time with a twist. Instead of filling the balloon with air, lets make it a little more fun. Lets try the experiment with a water balloon! Carefully stretch the mouth of the balloon over a water faucet and slowly fill the balloon with water. Then blow in a little air and tie it off.
At this point, work over a sink or outside, just in case things don't work as they should. Once again, light the candle, and hold the balloon over the candle, just at the top of the flame. What happens? You probably expected the balloon to pop, getting you wet. Instead, the bottom of the balloon turned black, but it did not pop. Why?
Understanding the Science
Water is very good at soaking up heat. Because the balloon is very thin, heat energy passes through it quickly heating the water on the inside. As the water near the flame starts to get hot, it rises, letting cooler water take its place to soak up more heat. This process lets the water balloon absorb a tremendous amount of heat without popping.
The black stuff on the balloon is the element carbon. It did not come from the balloon. Instead, it was deposited by the candle flame. The balloon has not been burned or damaged.
The idea of absorbing heat to control it is a very useful idea indeed. Firefighters use it to protect themselves while they are fighting fires. The radiator in your car absorbs heat from the engine to keep it from overheating. Heat sinks in computers absorb heat to protect delicate circuits. The idea even applies to ice cream, which absorbs the heat from hot fudge sauce, cooling it enough so you can eat it without burning your mouth. That sounds like an experiment worth trying.
Have a wonder-filled week!
Robert Krampf's Experiment of the Week: #483 Why Wet Things Don't Burn?
This week's experiment was inspired by my recent science video about how to hold a balloon in a candle flame without popping it. It started me thinking about why water is so effective at stopping fires.
*WARNING* This experiment involves the use of fire. Be safe, and be sure that there is an adult with you to help.
To try this, you will need:
paper towels
kitchen tongs or pliers
a lit candle or a lighter
a bowl of water
Begin by tearing a strip of paper towel about an inch wide and a couple of inches long. Hold it in the tongs and place it over the flame of the lighter. What happens? It quickly catches fire, just as you would expect. Put the burning paper into the water to put out the flames.
Then tear another strip of paper towel the same size. Hold it with the tongs, but this time dip in into the water first. Once it is wet, hold it in the flame. What happens this time? The paper turns black, but it does not burn. Even the black color does not come from the paper. Instead, it is carbon soot that comes from the flame. As long as the paper is wet, it will not burn. Why?
Understanding the Science
Some things are so common that we just accept them without wondering why. Water puts out fires, so of course wet things don't burn. But why? There are several things that add together to give water its fire quenching ability.
First, water does not burn. Why not? After all, it is made up of hydrogen and oxygen, both very flammable gases. When you burn fuel, it combines with oxygen. Last week, we saw that when we burned iron, it bonded with oxygen to become iron oxide. The carbon found in many fuels will bond with oxygen to become carbon dioxide. The hydrogen in water is already bonded to oxygen, so it is the same as if it had already been burned.
Second, water absorbs a lot of heat. Every material has a property known as specific heat. That is the amount of energy that it takes to raise the temperature of one gram by one degree. Water has a high specific heat, which means that it can absorb a lot of heat energy before it gets hot enough to boil. At the point where it boils, it absorbs even more heat, to give the molecules enough energy to change from a liquid to a gas. With the water absorbing all that heat, the wet fuel does not get enough heat for it to burn. That is how the balloon in the video was protected from the flame. It is only when the water has evaporated that the fuel can finally get hot enough to catch fire.
Water also separates the fuel from the oxygen it needs to burn. A coating of water provides a barrier to keep oxygen away from the fuel. Without that oxygen, the fuel won't burn.
All these things combine to explain why wet things don't burn.
Safety
With that said, it is important to mention that there are some fires that you should never use water on.
Never put water on an electrical fire. Water conducts electricity, and it could provide a connection between you and the electric wires.
Never use water on grease or oil fires. Water is heavier than the oil, so instead of floating on top, where it would block the oxygen, it sinks to the bottom. There it absorbs enough heat to change into steam. The rapidly expanding steam throws the burning oil in all directions, spreading the fire instead of putting it out.
That is why you should always have an approved type ABC fire extinguisher in your kitchen. They are inexpensive and can save your kitchen and your life.
Have a wonder-filled week!
Robert Krampf's Experiment of the Week:
#492 Building a Nest
This week's experiment is one that we used for teaching about birds back when I worked in the Education Department at the Memphis Pink Palace Museum. On our trip, we went by to say Hi to old friends, which brought back tons of great memories. This is one of the fun things my brain dredged up.
Look at some bird nests. You can either search your yard ( just look, don't touch or bother the nest), visit your local Nature Center, or search the Internet. A quick Google Image search for "bird nest" came up with over 175,000 images of bird nests. Look at the wide variety of nests, from huge Bald Eagle nests that can weigh more than a ton, to the marvelous nests that Hummingbirds build from spider webs. They truly are amazing, but how hard are they to build. That is what we will find out.
To try this, you will need:
Tweezers
several marbles
sticks
grass
string
leaves
hair
other things you may find in your yard
OK, the task is simple. Collect your materials from the yard, and then try to build a bird nest. You can select from anything in your yard that a bird might use. Think about the different nests you have seen, and what they were made of. Sounds like an easy project, right? Oh, one more thing. You have to collect the materials and build the nest using the tweezers. Birds don't have hands, and most of them make very little use of their feet in nest building. For most birds, their single tool is their beak. You don't have a beak, so you get to use the tweezers instead.
Your goal is to make a nest that would sit in a tree or a bush, and that would hold several bird eggs, or in our case, glass marbles. Trees and bushes are exposed to the wind, so the nest has to be sturdy enough so that it will hold the marbles, even when you shake the nest to simulate wind blowing the bush. You are limited to materials a bird would use. That rules out wrapping your nest in Duct tape or using glue to hold it together. Some birds do use their sticky saliva as a glue to hold the nest in place. In fact, nests made from the saliva of certain cave swifts are used to make Birds Nest Soup, a Chinese delicacy. Yum! I love Birds Nest Soup, even though I know it is made of bird spit. Feel free to use spit on your nest, if you think that will help.
When you are done with your nest, test it with the marbles and some gentle shaking. If it holds together, congratulations! Take a photo and email it to me. I will post the nests on my blog (http://www.thehappyscientist.com). Be sure to send your name, age, and what materials you used, to post with your nest photo.
When you are done, look back over the photos of the bird nests. You should then have a true appreciation of the skill these amazing creatures have, to build such elaborate structures with just their beak. Imagine trading in your hands for a beak. Just imagine how much work it would be to eat an entire bowl of ice cream with just a beak! Now that is something worth experimenting with!
Have a wonder-filled week!
Robert Krampf's Experiment of the Week:
#496 Which is the Magnet?
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This week's experiment is a fun science puzzle involving magnets. To try it, you will need:
a strong magnet (available at most hardware stores)
three paper clips
Straighten two of the paper clips, so that you have two long, fairly straight pieces of wire. Get both as straight as you can. Place one aside. Hold the other, and rub one end of the magnet along the paper clip, starting at your finger, and moving to the other end. Move the magnet away from the metal and repeat the process. Keep stroking the magnet along the paper clip, always in the same direction, for about 40 strokes. By doing this, we are magnetizing the paper clip.
Test the magnetized paper clip by bringing one end of it near the extra paper clip, the one that you did not straighten. If your paper clip is magnetized enough, it should attract the other clip. If not, try again with the procedure above.
Once you have the paper clip magnetized, you are ready for the challenge. Put both of the straightened paper clips together. Mix them until you are not sure which is which. The challenge is to figure out which one is the magnet and which is not, but you cannot use ANYTHING else to test with. No fair using the third paper clip, iron filings, a compass, or anything else. You are also not allowed to break the paper clips. The two straightened clips are all you need to figure it out.
So, how do you find out which is which? If I told you, you would just say, "Oh that makes sense." instead of really trying it. If you are really patient, you could wait until next week for the answer, but I bet you have enough scientific curiosity to actually get the materials and try it yourself.
Have a wonder-filled week!
Krampf je na http://www.krampf.com/
Poučan topic
Saradadevii, baš mi je Krampf trebao
Jučer sam s Markom palila različite materijale da mu pokažem razliku između prirodnih materijala i plastike.
Nešto za prvačiće. Kopiram jedan radni listić:
JE LI LAKŠE PLIVATI U SLATKOJ ILI MORSKOJ VODI?
Materijal i pribor: 2 čaše, topla voda, sol, žličica, 1 jaje
Postupci pri radu:
1.Ulij vodu koju piješ do polovice čaše. Kakvog je okusa voda koju pijemo?
2.Stavi jaje u tu čašu s vodom koju piješ. Što se događa?
3.Ulij u drugu čašu vodu i stavi u nju više žličica soli i promiješaj. Kakvog je okusa ta voda?
4.Stavi jaje u tu čašu sa slanom vodom. Što se događa?
5.Nacrtaj svoje istraživanje.
Opažanje:
Kada jaje tone, a kada pluta?
Zaključak:
Što zaključuješ, je li lakše plivati u morskoj ili slatkoj vodi? Zašto?
LJETO JE, KAKO SE ODJENUTI?
Materijal i pribor: crni papir, bijeli papir, gumice, 2 čaše, voda
Postupci pri radu:
1.Omotaj jednu čašu bijelim papirom i pričvrsti ga gumicom.
2.Omotaj drugu čašu crnim papirom i pričvrsti ga gumicom.
3.Obje čaše napuni vodom tako da ne smočiš papir.
4.Ostavi čaše na mjestu gdje ima mnogo sunca 2 sata.
5.Nakon 2 sata prstom probaj koja je voda toplija.
6.Nacrtaj svoje istraživanje.
Opažanje:
Koja je voda toplija?
Koji je papir privukao više sunca i topline?
Zaključak:
Koje bi boje trebala biti naša odjeća da nam ne bude vruće?
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