Physics P1: Conservation and Dissipation of energy

What is a system?

An object or group of objects.

What is a closed system?

A system where no energy is transferred to or from the surroundings.

What is work done?

Energy transferred when a force moves an object.

What is dissipation?

Energy transferred to less useful stores, often as heat to the surroundings.

What is efficiency?

A measure of how much energy is usefully transferred.

Name five energy stores.

Kinetic, gravitational potential, elastic potential, thermal, chemical.

Name three more energy stores.

Nuclear, magnetic, electrostatic.

Name four ways energy can be transferred.

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

What happens when a moving car slows down?

Energy transfers from kinetic to thermal stores (brakes and surroundings).

What happens when a kettle heats water?

Electrical energy transfers to thermal energy in the element and water.

What happens when a ball is fired with an elastic band?

Elastic potential energy transfers to kinetic energy.

What happens when a battery-powered toy car moves?

Chemical energy transfers to kinetic energy.

Equation for work done?

Work = force × distance

Equation for gravitational potential energy?

GPE= m x g x h

Equation for kinetic energy?

Ek=12mv2E_k = \frac{1}{2}mv^2Ek​=21​mv2

Equation for elastic potential energy?

Ee​=21​ke2

Equation for power (energy)?

Power = energy ÷ time

Equation for power (work)?

Power = work done ÷ time

Equation for efficiency (decimal)?

Efficiency = useful energy ÷ total energy

How to calculate efficiency as a percentage?

Multiply the decimal by 100 and add %

What is the unit of energy?

Joule (J)

What is the unit of power?

Watt (W)

What is one joule of work?

When a force of 1 N moves an object 1 m.

How can frictional energy loss be reduced?

Lubrication.

How can air resistance be reduced?

Streamlining.