Science Fair
Originally uploaded by raisingk.
K did a science fair project a few weeks ago with her 3rd grade class. She wanted to do something about skating and curling, so she called her project "Ice Science." It turned out pretty neat!
I really struggled with how much or how little to help her. Seeing all the presentations, I realized that other parents struggled as well :-) I ended up helping her only with the physics equation and calculations she was trying to do. She understood the concept, but doesn't yet have the math skills to really figure out all the numbers.
In case you are interested, I copied her full report below:
I ice skate so I wanted to learn about the science of curling and ice skating. I wanted to know why ice is slippery for curling stones and skate blades. I also wanted to know about spinning on ice and why skaters spin faster in some kinds of spins.
Ice is slippery because there is barely any friction. Friction is what makes things slow down. On ice things don’t slow down much. If you slide something on the ice, it keeps going for a while. So when I skate, it’s hard for me to stop. The ice makes me go fast. The curling stone works the same way. When a curler slides the stone, it goes for a long time. Curlers make the stone go even farther by sweeping the ice. That does a lot to help it keep going because it makes even less friction.
I used pennies, tin foil, wax paper, and a hard slide to show about friction on ice. I have two pennies. I put crumpled tin foil on half of the hard surface and smooth wax paper on the other half. Then I took the two pennies and put one on each side. I let them slide down to see which one got to the end first. The penny on the wax paper side always got to the end first. The wax paper is like ice because it has only a little friction. The crumpled tin foil side has more friction.
I also learned about spinning. I learned that your radius gets bigger when you spread your arms out and you don’t go as fast. When I spin, I put my arms across my heart and tuck one leg in by my knee. I am supposed to do this so I go really fast. If I leave my arms out, I don’t go fast. For a scratch spin, your arms are straight up and legs are crossed at the ankle so you are straight up and down. That is the fastest spin. The slowest spin is the camel spin. You do a camel spin by putting your leg out behind you, and your arms out to the side. You can’t spin very fast that way.
There is angular momentum in spins. Angular momentum (L) equals mass (m) times velocity or speed (v) times radius (r). L=mvr. This shows us that keeping your arms in and out (r) changes your velocity (v). So when your arms are out, your radius is big and that makes your speed small. When your arms are in, your radius is small and that makes your speed big.
I tested this. I did a one foot spin with my arms in and out. With my arms in I went super duper fast. My mom timed me and counted my spins. With my arms in, I did 3 turns in 1.5 seconds. My mom calculated that I did 120 revolutions per minute. This is my velocity. My radius with my arms in is 30cm. My mass is 25 kg. So, my angular momentum is 25kg times 120 rpm times 30cm, which equals 90,000.
Angular momentum is not supposed to change. So with my arms out my radius gets bigger and that should make my velocity smaller. My radius with my arms out is 60cm. That is double, so my speed should be half, which is 60 rpm. My mom timed me again with my arms out. I did 3 turns in 2.1 seconds. My mom calculated that I did 86 revolutions per minute. That is faster than I expected. Maybe I went faster because I’m small. Maybe there was something wrong with the calculating.
I can’t do a camel spin yet. But I think I will go slower. My mom measured my leg and found out it is 75cm. That will be the radius. That will make my speed even smaller. I’ve watched the famous skaters and seen many of them do camel spins and scratch spins. The scratch spins make the speed much bigger, and the camel spins don’t go fast.
I can show this by spinning in an office chair. My friend S and I were playing at K’s house and we found an office chair that wasn’t being used. So I got in the office chair and S spun me around. I tried it first with arms out, and then in. I went faster with my arms in. Then, with my arms out, I only went 10 revolutions in 30 seconds. I went around 30 more times with my arms in. Spinning faster was better.
Works Cited
Gardner, Robert. Science Projects About the Physics of Sports. Berkeley Heights, NJ: Enslow, Inc., 2000.
Ontario Science Center. Sportworks. Reading, MA: Addison-Wesley Company, Inc., 1989.
"Science Fair." Dragonfly TV. 2006. PBS. 9 Apr. 2007 http://pbskids.org/dragonflytv/scifair/index.html.
"The Biomechanics of Skating: Conservation of Angular Momentum." Winter Olympics: Sport and Science. Apr. 1998. Montana State University - Bozeman. 9 Apr. 2007 http://btc.montana.edu/olympics/physbio/biomechanics/cam-intro.html.
