A Science Experiment for Kids: Gravity and Centrifugal Force
Okay, Gravity is explained by Newton’s law, which states that everything, absolutely everything, has a gravitational force that attracts, or pulls on everything else. The bigger the thing, or the more mass it has, the more gravity it exhibits. That’s why we all circle the sun, which is the biggest thing in our stellar neighborhood. It is also why we don’t go floating off this lovely green and blue ball we call Earth and explains a whole host of other things, like why the planets are round and such. The farther things are away from each other, the less gravity we have, which is why astronauts are relatively weightless is space. But, what is Centrifugal Force, and why do some people call it a ‘false’ force?
Image via Wikipedia
Centrifugal Force is called false because it creates a ‘false’ gravity. The amount of that false gravity depends on the mass of the thing, the speed of rotation and how far away the thing is from the center of rotation. The force created is actually part of Newton’s law of Motion, but for our purpose today we are going to call it centrifugal force. I describe it as the feeling you get when your older brother grabs your arms and spins you about, or how you feel on a carnival ride that spins and is designed to make you loose your lunch on your chums. You can feel yourself being spun away from the center of the rotation.
To get a look at gravity and false gravity, you will need two round balloons, two small marbles, a healthy set of lungs, and three sets of hands to drop three things from the same height.
Blow up one balloon and tie it off. Put the marble into the second balloon and blow up the balloon to about the same size as the first. (Okay, adults, you do the blowing up with the marble balloon combo. It would really ruin everyone’s day if one of your kids inhaled the marble right out of the balloon. Unlikely, but….)
Okay, take the balloon with the marble and start moving it in a circular motion to really get that marble spinning. Let it go and watch it wiggle and jerk as it falls as the marble keeps spinning creating centrifugal force, and gravity attracts the whole thing to the center of the Earth.
Now take the marble, the plain balloon and the marble balloon and the three sets of hands. Get the marble spinning again and drop all three from the same height. The mass of the marble balloon combo should be greatest, but what hits the ground first? The marble, usually followed by the balloon and then the balloon marble combo. Have the kids discuss the results. Do this several times, as results will vary. If you want to bring up Chaos Theory, now’s the time…
Now a fun game is to take these balloons and marbles and call them weasel balls and let the kids spin them about and play with them for a bit. You will get some popping as the balloon was designed to contain the mass of air, not a spinning marble, but try to save one that you have spun a bit. Take a measurement of that balloon and the balloon with no marble at the beginning, and then the next day. The balloon with no marble should be about the same and the balloon with the marble should be almost flat. Have your students talk about why that is. (The air escaped from the balloon with the marble faster as the ‘pours’ of rubber were stretched by the marble.)
Small word of caution: The marble balloons should never be batted about by the kids. You are not hitting your friend with a fun and playfully soft balloon, but by a hard and unforgiving marble. Ouch! Also, when they pop, and they will eventually, the marble could go flying. That being said, have fun with science!
Other science things for kids: