Kinetic Energy (Cambridge (CIE) IGCSE Physics): Revision Note

Kinetic energy

Extended tier only

• Energy in an object's kinetic store is defined as:

The amount of energy an object has as a result of its mass and speed

• This means that any object in motion has energy in its kinetic energy store

  • If an object speeds up, energy is transferred to its kinetic store

  • If an object slows down, energy is transferred away from its kinetic store

Kinetic energy of a moving object

A moving car has energy in its kinetic store

Kinetic energy equation

• The amount of energy in an object's kinetic store can be calculated using the equation:

$E_k=\frac{1}{2}m{v}^2$

• Where:

  • $E_k$ = kinetic energy, measured in joules (J)

  • $m$ = mass of the object, measured in kilograms (kg)

  • $v$ = speed of the object, measured in metres per second (m/s)

• The kinetic energy equation demonstrates that if the mass of an object is doubled for a given speed, then its kinetic energy will double

  • This is because kinetic energy is directly proportional to mass

  • $E_k\propto m$

• If the speed of the object is doubled for a given mass, it will have four times the kinetic energy

  • This is because kinetic energy is directly proportional to velocity squared

  • $E_k\propto v^2$