Edexcel iGCSE Physics -4.14 Kinetic Energy- Study Notes- New Syllabus

Kinetic Energy

Kinetic energy is the energy an object has because it is moving. Any object with mass that is in motion possesses kinetic energy.

Relationship Between Kinetic Energy, Mass and Speed

The kinetic energy of a moving object is given by:

\( \mathrm{kinetic\ energy = \dfrac{1}{2} \times mass \times speed^2} \)

\( \mathrm{E_k = \dfrac{1}{2}mv^2} \)

• \( \mathrm{E_k} \) = kinetic energy (joule, J)
• \( \mathrm{m} \) = mass (kilogram, kg)
• \( \mathrm{v} \) = speed (metre per second, m/s)

Understanding the Equation

• If the mass doubles, kinetic energy doubles.
• If the speed doubles, kinetic energy increases by a factor of four.
• This shows that speed has a much greater effect on kinetic energy than mass.

This is why vehicles travelling at high speeds have much larger kinetic energies.

Energy Transfer Explanation

• Work done on an object increases its kinetic energy.
• When an object slows down, its kinetic energy is transferred to other energy stores.
• For example, braking transfers kinetic energy into thermal energy.

Key Idea

• Kinetic energy depends on both mass and speed.
• Speed has a squared effect.
• Kinetic energy is measured in joules.

Important Points to Remember

• Speed must be in m/s.
• Mass must be in kg.
• Always square the speed before multiplying.