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Grades 9 and 10 Intermediate About 20 min Version 1 Awaiting review Premium

Potential and kinetic energy on a ramp

An object raised above the ground has gravitational potential energy: PE = m × g × h. When it rolls down a ramp, this energy changes into kinetic energy, the energy of movement: KE = ½ × m × v². Energy is never created or destroyed, only changed from one form to another. On a smooth ramp almost all the potential energy becomes kinetic energy. On a rough ramp friction changes some of it into heat, so the trolley reaches the bottom more slowly.

What you will learn

  • Calculate gravitational potential energy using PE = mgh.
  • Use the conservation of energy to find the speed at the bottom of a ramp.
  • Explain where the 'missing' energy goes on a rough ramp.

Before you start

  • Know that energy is measured in joules (J).
  • Know that weight = mass × g.

Materials

  • Trolleys of 0.5 kg, 1 kg and 2 kg

Equipment

  • Ramp that can be set at different heights
  • Light gate or stopwatch to measure speed
  • Metre rule

Procedure

  1. Release the 1 kg trolley from three different heights on the smooth ramp and record each run.
  2. Release a 2 kg trolley from the same height as one of your runs and compare the speed.
  3. Change to the rough ramp, release the trolley again and see where the energy goes.

How this simulation is simplified

  • g is taken as 10 N/kg.
  • The smooth ramp has no friction or air resistance; the rough ramp turns a fixed 25% of the energy into heat.