Science Experiment: Bottled Tornado

I've seen this before, at the Thinktank and at a science day at the Erasmus Darwin house, but I never stopped to think about why it works until now.  What's supposed to happen, is that we make a tornado inside  a bottle.  We do this by getting two bottles, and making half centimeter holes in each of the bottlecaps.  We then glued the bottle caps together (we had to use really strong glue and let it dry for a long time).  Then we filled one bottle with water, and we put in some pink food colouring and glitter so we could see the currents in the water.  We screwed both bottles into the glued double bottlecap, to make this (except not sideways):

If you spin the top bottle carefully enough and hard enough, the water will start spinning around, and it will move along the sides of the bottle.  After we stop spinning, the water keeps moving -- this is called centripetal force.  I've heard of centrifugal force, which my dad says is the opposite of centripetal force, but I'm still confused.  He said centripetal force keeps "tripping" you in a circle, where centrifugal (with an "f" in it) force makes you "fly" off.  I don't think that helps.

Anyway, as the water goes along the side of the bottle, some of it slips through the outside of the hole in the bottlecap.  But this only happens if the water is spinning -- if it's not moving, the water doesn't go through the hole.  I learned that the empty bottle on the bottom is not actually empty, but full of air.  And if water is to go in to the bottom bottle, air must somehow escape from it, because the air is stopping the water from coming through.

When the water is spinning along the sides, air can come up through the middle -- and that's what a tornado does (except that's cold air failing with hot air).  So the tornado lets water go into the bottle bottle at the same time that air goes into the top!

Tornadoes are deadly.

Science Experiment: Splitting Light

In this experiment, we actually split white light (which is made of all colours) into a rainbow (the different colours that make up white light).  We did this by making a slit in a piece of cardboard, that was just big enough to let a bit of light through.  Because the slit was so small, each colour of light could only fit through at different angles.  We use a glass jar filled with water to act as a lens, putting the card with the slit on one side of the jar:

When we shined the light through the slit, the water carried the light and refracted it out at the different angles.  On the other side of the jar, if we held the light at just the right angle, there was a spot made up of a rainbow with all the colours split apart.  This is one of the best colour spots:

I learned that black is not one of the colours that makes up white light, because black is actually just darkness (no light at all).

Science Experiment: Why is the Sky Blue

In this experiment, I was supposed to learn about why the sky looks blue.  Light is made up of all the colours (except black, which is just no light), and sometimes when light is shining on something, only some of the colours get through to the other side.

To test this, we put some milk (just a little) in a jar full of water.  Then we shined a flashlight into the jar in a dark room.  When the light shone down on the top of the jar, the milky water on the top looked blue, like the sky.  When we shined the light through the side of the jar, the light coming out the other side looked red.

Here's the flashlight, jar and milky water we used:

The different colours are supposed to be because the particles of milk block the light so that short-wave light gets caught and bounced around (at the top of the sky), while long-wave light makes it through the other side (sky at sunset or sunrise).  I'm not sure it makes sense, because milk, the air in the atmosphere, and light aren't things that I think of as interacting.  My dad says the blue colour is actually just mostly light reflected from ozone molecules in the atmosphere -- that they are blue, just like my blue school bag.

My dad gave me a different example of only certain light passing through, and I thought this was much better:

Blood and flesh only lets through red light, like a sunset!