3-NRG-02

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Outcomes

  • Pupils can recall the Law of the Conservation of Energy.
  • Pupils understand how the conservation of energy applies in real-life contexts.
  • Pupils understand the idea of efficiency and can calculate the efficiency of of energy transfers.

Specification References

4.3 understand that energy is conserved

4.4 recall and use the relationship: Efficiency = useful energy output/total energy input

Starter

  • Select a pupil and demonstrate that a heavy pendulum bob released from the tip of their nose never returns far enough to strike them.

Main Body of Lesson

  • Following on from the starter elicit the idea that in the pendulum system there is a constant back-and-forth transfer between GPE-kinetic-GPE but that during each swing some kinetic energy is lost as thermal energy due to friction (elicit "air resistance" as a type of friction).
  • Move on to discussing bouncy balls. Ask pupils how they would measure the "bouncyness" of a ball.
    • Elicit the energy transfer as gravitational potential to kinetic to elastic potential to kinetic to gravitational potential.
  • Pupils carry out experiment to find the efficiency of the return of energy of a bounce, they could also find the coefficient of restitution of bouncy ball.
  • Discuss results of bouncy ball experiment. Elicit the idea that the bouncy ball loses a "fixed" percentage of its kinetic energy each time, resulting in a graph that is curved.
    • Suggestion: Compiling all pupil results into one spreadsheet and averaging out produces a very good exponential curve.
  • Pupils carry out experiment to investigate the effect of temperature on the coefficient of restitution of a squash ball.
  • Discuss results of squash ball experiment. Elicit the idea that the heated balls bounce higher (have a higher coefficient of restitution) than the cooler ones. Pupils may notice that for different balls the difference between hot and cold is different - there is no fixed relationship that applies to balls of different colour.

Practicals/Demonstrations

  • Conservation of energy demonstration using volunteer pupil and large pendulum.

Finding the coefficient of resitution of a bouncy ball

  • Each group has one bouncy ball and a metre rule.
  • Pupils measure the maximum height a bouncy ball reaches after being dropped onto a hard surface (e.g. laboratory floor) from a height of one metre.
  • Pupils then drop the ball again from the previous height reached. By doing the experiment this way they find the height of each bounce in a series without having to do it all at once.

Comparing squash balls

  • Each group has three squash balls of each colour.
  • One ball of each colour should be made hot, one cold, and one kept at room temperature.
  • Pupils drop each ball from a height of one metre and record the height they reach on their first bounce.

Plenary

  • Discuss the energy transfers involved; this is an excellent opportunity to begin considering energy "losses" in a more rigourous manner.

Homework

Additional Information

Resources Required

Skills Addressed

  • Understanding conserved quantities.

Safety/Hazards

  • Ensure that pupil remains absolutely stationary during pendulum demonstration to avoid the bob striking them.

Energy Outline

Energy (3rd Form)