Energy yr 9

Definition of Work Done

The energy transferred when a force moves an object through a distance.

Work Done equation

Work Done (W) = Force (F) × distance (s)

The unit of Work Done

Joules (J) - where 1 Joule is equal to 1 Newton-metre.

Definition of Power

The rate at which energy is transferred (or the rate at which work is done).

Power equation (Work)

Power (P) = Work Done (W) ÷ Time (t)

Power equation (Energy)

Power (P) = Energy Transferred (E) ÷ Time (t)

The unit of Power

Watts (W) - where 1 Watt is equal to 1 Joule per second.

Definition of Efficiency

The proportion of total input energy/power that is converted into useful output.

Efficiency equation (Energy)

Efficiency = Useful output energy transfer ÷ Total input energy transfer

Efficiency equation (Power)

Efficiency = Useful power output ÷ Total power input

Kinetic Energy definition

The energy an object has due to its motion.

Kinetic Energy equation

Ek = 0.5 × mass (m) × speed² (v²)

What happens to Kinetic Energy if speed doubles?

The Kinetic Energy quadruples (increases by 4x) because speed is squared in the equation.

Gravitational Potential Energy (GPE) definition

The energy stored in an object due to its position in a gravitational field.

GPE equation

Ep = mass (m) × gravitational field strength (g) × height (h)

Standard value of 'g' on Earth

9.8 N/kg

Elastic Potential Energy (Ee) definition

The energy stored in a stretched or compressed elastic object (e.g., a spring).

Elastic Potential Energy equation

Ee = 0.5 × spring constant (k) × extension² (e²)

Law of Conservation of Energy

Energy cannot be created or destroyed, only transferred, stored, or dissipated.

Dissipated Energy

Energy that is transferred to non-useful stores (often as thermal energy to the surroundings).

Closed System (Energy)

A system where no energy or matter can enter or leave; the total energy remains constant.

Lubrication role

Reduces friction between surfaces, decreasing the amount of energy dissipated as heat.

Thermal Insulation role

Reduces the rate of energy transfer to the surroundings (wasted heat).

How to calculate final speed of a falling object (Energy)

Set GPE at top = KE at bottom (mgh = 0.5mv²), then solve for 'v'.

Relationship between Joules and Newtons

1 Joule = 1 Newton × 1 Metre

Net change in total energy in a closed system

Zero (Total energy is constant).

Power of 1 kilowatt (kW) in Watts

1000 Watts.

Why can efficiency never be 100%?

In almost all transfers, some energy is dissipated (wasted) as thermal energy.