Changes in Energy Stores — Kinetic and Gravitational

In this lesson you will learn how to calculate kinetic energy and gravitational potential energy, and how these two stores are linked when objects rise or fall. These equations are essential for the AQA GCSE Combined Science Trilogy specification (8464), Section 6.1.

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Kinetic Energy

Kinetic energy is the energy stored in a moving object. The faster the object moves and the greater its mass, the more kinetic energy it has.

The Equation

$E_k = \frac{1}{2} m v^2$Ek​=21​mv2

Where:

• $E_k$Ek​ = kinetic energy in joules (J)
• $m$m = mass in kilograms (kg)
• $v$v = speed in metres per second (m/s)

Key Features of the Equation

• Kinetic energy is proportional to mass: double the mass → double the kinetic energy.
• Kinetic energy is proportional to the square of speed: double the speed → four times the kinetic energy.

Exam Tip: The $v^2$v2 relationship is tested frequently. If a car doubles its speed, its kinetic energy quadruples — this is why braking distance increases so sharply at higher speeds.

Worked Example 1