Physics Chapter 2

Chapter 2

When a ball falls in air, it loses gravitational potential energy and gains kinetic energy. When an electric heater is switched on, it transfers electrical energy by heating.

A person going up in a lift gains gravitational potential energy. The list is driven by electric motors. Some of the electrical energy supplied to the motors is wasted instead of being transferred to electrical energy.

An electric heater - useful energy = heat, wasted energy = lightA television - useful energy = light and sound, wasted energy = heatAn electric kettle - useful energy = kinetic and heat, wasted energy = soundHeadphones - useful energy = sound, wasted energy = heat

The useful energy from a machine is always less than the total energy supplied to it. Friction between the moving parts of a machine causes energy to be wasted by the machine. Because energy is conserved, the energy supplied to a machine is the sum of the useful energy from the machine and the energy wasted by the machine.

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