P1 - Conservation and dissipation of Energy

Name the five energy stores

Kinetic, gravitational potential, elastic potential, thermal, chemical

Name the four ways in which energy can be transferred

Heating, waves, electric current, mechanically (by forces)

What is a system?

An object or group of objects

What is a closed system?

A system where no energy can be transferred to or from the surroundings - the total energy in the system stays the same

What is work done?

Energy transferred when a force moves an object

What is the unit for energy?

Joules (J)

What is one joule of work?

The work done when a force of 1N causes an object to move 1m in the direction of the force

Describe the energy transfer when a moving car slows down

Energy is transferred mechanically from the kinetic store of the car to the thermal store of its breaks. Some energy is dissipated to the thermal store of the surroundings.

Describe the energy transfer when an electric kettle is used to heat water

The electric current in a kettle transfers energy to the heating element’s thermal store - energy is then transferred by heating from the heating element’s thermal store to the thermal store of the water

Describe the energy transfer when a ball is fired using an elastic band

Energy is transferred mechanically from the elastic store of the elastic band to the kinetic store of the band - some energy is dissipated to the thermal store of the surroundings

Describe the energy transfer when a battery powered toy car is used.

Energy is transferred electrically from the chemical store of the battery to the kinetic store of the toy car - some energy is dissipated to the thermal store of the surroundings

Describe the energy transfer when a falling apple hits the ground.

Energy is transferred from the kinetic store of the apple and dissipated to the thermal store of the surroundings by sound waves

Name the unit that represents one joule transferred per second.

Watt (W)

A motor is 30% efficient. What does this mean?

30% of the energy is usefully transferred and 70% is dissipated