3-NRG-02

Outcomes

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

Specification References

• 4.3

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

• • Elicit the idea that 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.
  • Elicit the energy transfer as gravitational potential to kinetic to elastic potential to kinetic to gravitational potential.
• Pupils carry out experiment to find 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.
• 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.

Additional Information

Resources Required

• Large heavy pendulum suspended from ceiling.
• Bouncy balls (1 per group)
• Metre rules
• Squash balls (3 of each colour per group (with sharing between groups 12 each of four colours works well))
• Spreadsheet with example results and graphs (SST001)

Skills Addressed

• Understanding conserved quantities.

Safety/Hazards

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