Our Olympic-themed Physics Open House is Sunday, Oct 5, 1-4 pm. Come join the fun!
Demo ideas we talked about (I'll add more if I remember more - remind me in the comments, if you think of something I missed):
Friction and Drag - Friend and Foe
Swimmers swim faster if there is low drag. Special swim suits, shaving arms and legs, etc. Demonstrate using different materials pulled through a pan/pool of water - smooth surface vs furry surface, flat surface vs streamlined surface, wide surface vs narrow surface, water vs thicker fluid?
On the other hand, swimmers use drag to propel themselves along. Demonstrate with kid on cart, they push a paddle in the water and the water pushes them the opposite way (action force and reaction force). Runners also use friction in the same way to propel themselves forward. Video of runner slipping?
Skaters reduce friction on ice, because a bit of ice melts under their skates, so they are riding on a thin film of liquid water. Even less friction if riding on a thin film of air. Demonstrate by racing solid block, drops of water, and drops of liquid nitrogen (which vaporizes, creating a thin film of air for it to ride on).
Rotation - Divers and skaters and bikers
Bicyclists turn by leaning (video). This a rotational form of action-reaction. Demonstration: If kid on a cart pushes on wall, it will push back on them. If a kid on platform (which is free to rotate) changes the rotation of a spinning wheel, it changes the kids' rotation, too.
Divers and skaters can speed up their rotation by changing their moment of inertia (bringing their mass closer to the center of rotation). Demonstrate by rotating kid on platform with masses in outstretched arms; when they bring their arms closer to the center of rotation, their rotation will speed up.
Elasticity - Bounce!
How bouncy a ball is depends on its elasticity. When it hits a surface, it stops for a moment losing all its kinetic energy. Elasticity is a measure of how much of that energy is stored in the deformation of the ball, and how much is dissipated or lost. Demonstrate by bouncing different kinds of balls (basketball, soccer, handball, table tennis, tennis, volleyball), including "happy" and "sad" balls. Also demonstrate how a spring stores energy when squished (projectile launcher?), but Playdoh dissipates it.
Projectile motion - Flying through the air
In field events, basketball, ski jumping, shooting, archery, etc, a projectile moves up and down while at the same time moving forward. You can't aim straight at your target, because the projectile will drop during its flight and arrive below the target. The up and down motion is (approximately) independent of how the object is moving sideways. Maximum range is achieved at (approximately) 45o. Demonstrate via projectile launcher and/or trebuchet.
Relative motion - Why shotputters spin and javelin throwers run
Since they are moving when they release the projectile, it moves with a velocity equal to the sum of the velocity of the projectile relative to you and your velocity relative to the ground. Demonstrate with a moving projectile launcher. We need to test this one to see if it works.
