Physics for Kids: Light

 I think we've settled into a pattern with the physics: the kids watch the Bill Nye episode related to the topic while I set up the experiments.

As soon as they finish, they are primed to  explore!

Light experiments are hard to photograph, but I got these LED finger lights a while back, partly to do light mixing experiments (they also make for great light up Easter egg hunts).

Kids are always told that yellow and blue make green (that's what the pipette and 96 well plate at the bottom are for: color mixing with liquid dyes).  This is true enough for pigment, but not for light.

If you mix all your paints together you get a muddy brown/black color.  If you mix all your light together, you get white.  I've done this before by taping colored lenses over flashlights, but the colored LEDs were easier, and there were enough for all the kids to experiment at once.

I also got to use my fancy set of lenses and prisms which I had picked up from a science supply store.  What worked best for us was to place, say, the convex lens against the wall and shine an LED through it, parallel to the wall.  You could see the patterns of refraction perfectly!

We also used my good spectrometer and a diffraction grating to look at the different wavelengths of light emitted by different sources.  We could also have used the home made variety, but my "good" spectrometer had calibrations so you can actually measure the wavelengths. I say "good" because it's less than $5 (actual laboratory spectrometers cost thousands).

We also looked at distortions caused by water.  The immutable "speed of light" is it's speed in a vacuum, light slows down as it passes through different densities.  Light moves more slowly through water than air, so if you put a pencil in a jar of water, it appears bent.

Interestingly, the kids were most fascinated by iridescence- the rainbow sheen of an oil slick.  In our case, we made it by dropping one drop of nail polish on to water (use a paper cup).  They were fascinated by the iridescence, by the rapid dispersion across the surface (changes in surface tension caused by the acetone base, I presume), and by the thin skin which hardened on the water surface.

************************************************************************

In other Physics news, I also did a lesson on simple machines.  The possibilities for experiments here are endless, but I decided to try a different tack.  After they watched the episode, I asked them to show me an example of each simple machine using their Bionicles.

They did an amazing job!  I forgot to take pictures.  A video of their explanations would have been priceless!  But they were great! :)

Physics for Kids: Electricity

I've decided to do a small low stress Physics Club.   Once or twice a week (depending on how much prep time I have), we dip into Mom's Magic Box of Physics (NO PEEKING!).

Inside the box we find a variety of experiments grouped around a theme.  Really, I am shamelessly following my favorite experiments from Janice Van Cleave's Physics for Every Kid.

 So this week we started with electricity (I don't think we need to do laws of motion again!).

We actually started with watching the Bill Nye episode on electricity, so we got a good discussion of the basics. 

Electricity is a moving current of electrons.  What will it move through and why?

We started with a D battery and a variety of conductors and insulators.  You need to warn the kids, if it makes a circuit, the metal will get quite warm, quite quickly, so be prepared to drop it!

Did you notice that the shiny things tend to be conductors?  They shine for the same reason they conduct electricity: lots of loose electrons!

The conductors get warm because  they are imperfect: they are offering resistance to the electrons, so some of the electrons' motion is being converted by friction into heat.

If you have electric heat (or an electric stove or toaster!) that's how it works.

We also did quite a bit with static electricity because it's easy to see exactly what you are doing (rubbing electrons off of your hair) and because it's really hard to build enough of a charge to electrocute anyone!

 We hung two balloons from thread in a doorway.

At first, the uncharged balloons hang loose.

Rub one balloon on a kid's head and the balloons stick together (the negative charge will be attracted to the neutral because it's more positive - opposites attract).


Rub the other balloon on a kid's head and the balloons spring apart because they are both negatively charged (likes repel).

And this negative charge will attract/be attracted to all sorts of things!

Tissue paper, glitter, lint, little paper tents in plastic cups, water, the wall, your head...

It's fun to try different things!

The most fun experiment was one where I couldn't take a picture, but if you only do one experiment do this one: go into a dark room with a balloon and a florescent light bulb.  Rub the balloon on someone's hair and bring it close to the light bulb.

That's why florescent bulbs take so much less energy to run!

The grand finale was our home made electroscope:

Kid's Rocket Science: First Law of Motion

 Shifting gears from Astronomy to Physics, today's class was about Newton's First Law of Motion: a body at rest tends to stay at rest, a body in motion tends to stay in motion, unless acted upon by an outside force.

We started out defining force as a push or a pull on something (although there are forces like drag that are a little less straight forward than "push/pull").

And we defined mass again: it's how much "stuff" is in you (as opposed to volume: the amount of space you take up). So, you can see that the scale measures a force (gravity pulling down on a certain amount of mass), while the balance measures mass (this much mass over here is equal to that much mass over there).

The first half of the law is easy to demonstrate: a body at rest (a lab assistant) tends to stay at rest, unless acted upon by an outside force (alarm clock).   I also set up a model rocket and let the kids do a countdown to... nothing happening.  Without the engine to provide an outside force, it just sits there!

But there are more fun ways to show this: we gave each kid a cup, a card (to set on the cup) and a quarter (to set on the card).

When you flicked the card away, the quarter tended to stay in place until acted upon by an outside force (gravity), at which point it fell into the cup.

We also did the quarter on the elbow trick. And I used a string of rubber bands to drag a large (smooth bottomed) rock.  You can measure the force it takes to move the rock by the length of the bands.  The bands stretch a long way to get the rock moving, but then they shorten up as it continues moving.

The fancy term for the first half of Newton's First Law is inertia, while the fancy term for the second half is momentum.  Once you start looking, there are practical examples of both everywhere!

Think about how difficult starting a hula hoop versus keeping it going or balancing a still bicycle, versus a fast moving bicycle.

Let alone biking up a big hill from a standing start!

Perhaps most importantly, these laws tell you exactly why you should wear seat belts.  To demonstrate this, we played a game I'll call Train Wreck.

I had a ll the kids form a train behind me, an off we went.

After we picked up some speed, I stopped quickly.  Train wreck!

There are some other fun ways to use momentum.

 For example, eggs.  Of these 18 eggs, 6 are hard boiled.  I had the kids spin them to determine which ones were raw( how's that for bravery in the name of science?!).

If you spin a raw egg, stop it briefly (with a light touch), and let go, the liquid inside will continue to spin,and the egg will turn.

You want us to what?

A hard boiled egg will take a tiny bit more energy to stop, but it will stay stopped.

 And, of course, there's always spinning around until you get really dizzy.  That's the momentum in the fluid of your semi circular canals, incidentally.

So that's about it.  Am I missing something?

Oh, yes, the rockets!!

This week's rocket is the balloon rocket.

We ran strings between chairs for a track (2 tracks per set of chairs so they could "race.").

We clipped a section of drinking straw  and put it on the string to attach the balloons to the strings.

We blew up the balloons (without tying them off) and gave it a go!  And it totally did not work.

I had only been able to find round balloons instead of long tubulat balloons.  The round balloons can't be oriented enough along the track to make this experiment work as planned.

So they took the balloons outside and raced them in crazy patterns on the lawn, so, no harm done!

My young cousin got the brilliant idea to put a penny in the balloon.  It takes a bit of shaking, but once the penny gets going, it spins along the interior of the balloon for a long time: inertia and momentum!!

At the end, we had a bit of extra time, so we threw Oob a little early birthday party, much to everyone's satisfaction.  Balloons and cupcakes, what's not to like?