Item NG075003: Assuming that no energy is transferred between a ball and the curved track it is moving in, or between the ball and the air around it, a ball on a curved track will reach a point as high as the point from which it started because as the ball moves down the track, its gravitational potential energy will change into motion energy, and as the ball goes up the other side, its motion energy will be changed back into an equal amount of gravitational potential energy.

Imagine a ball on a track where no energy is transferred between the ball and the track or between the ball and the air around it.  The ball starts from rest at the position labeled Start and goes down and then up the track toward Positions 1, 2, and 3.

What is the highest position the ball will reach before stopping and going back down the track?  Why?  (Remember that no energy is transferred between the ball and the track or between the ball and the air around it.)

  1. Position 1.  As the ball goes down one side, its gravitational potential energy will decrease and its motion energy (kinetic energy) will increase, but its motion energy will not increase enough for it to go past Position 1.
  2. Position 2.  As the ball goes down one side, its gravitational potential energy will change into motion energy (kinetic energy), and as the ball goes up the other side, its motion energy will be changed back into the same amount of gravitational potential energy it started with.
  3. Position 3.  As the ball goes down one side, its motion energy (kinetic energy) will be added to its gravitational potential energy, which gives it enough energy go higher than it started.
  4. The position the ball will reach depends on how much the ball weighs because gravitational potential energy and motion energy (kinetic energy) both depend on the mass of the ball.

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