# NYU Physics Demos

## Conservation of Energy I

Topics: Mechanics - Conservation of Energy, Kinetic/Potential Energy, Static Friction

Equipment: Aluminum loop track on wooden base, metal balls.

Setup: Place a ball anywhere on the track. The higher it is placed, the easier it will overcome the loop.

At the highest point of the track, the ball has the greatest possible potential energy because of its height: U=mgh. However, its kinetic energy is zero because it is not moving yet: T=(1/2)mv2. Of course, the total energy E=T+U. When the ball is released and starts to pick up speed, it will eventually reach its lowest possible point, and therefore lowest potential energy. Energy is not conserved because of resistive forces such as static friction and air resistance. These resistive forces dissipate energy to the outside world in the form of heat (thermal energy- the energy is not destroyed, but transferred to a different form). Since the ball lost energy, it may no longer have enough kinetic energy to reach the top of the loop (higher potential energy). If the ball was placed sufficiently high enough, it will have enough energy to overcome the loop, even though it lost some along the way. If the ball is placed at the exact height of the top of the loop and released, it will not reach the top of the loop, because at least a small amount of energy will be lost as it rolls down the track.

Location: B22

Notes: The track comes with two metal balls, and a holder for them. Please do not lose the balls.

Keywords: Energy, Roll, Ball, Friction, Gravity

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