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Kinetic Energy formula:
story, analogy and memory trick

The Kinetic Energy formula is KE = ½ × m × v². The kinetic energy of a moving object is half its mass times the square of its speed, so speed matters far more than mass.

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The Kinetic Energy formula

KE = ½ × m × v²
  • KEkinetic energy, in joules
  • mmass, in kilograms
  • vspeed, in m/s

The story

A cricket ball bowled at 70 km/h is easy to block. The same ball at 140 km/h carries four times the energy, because speed is squared. Doubling the mass would only double the energy, but doubling the speed quadruples it. That is why fast bowlers are dangerous.

Real-life analogy

Think of a vehicle on a highway. At double the speed it needs about four times the braking distance, because it has four times the energy to get rid of.

Memory trick

Say it as 'half m v v'. The speed appears twice, so it is squared.

Exam tip

Doubling the speed makes KE four times larger, while doubling the mass only doubles it. KE is never negative. The unit is the joule.

FAQ

Questions about Kinetic Energy

What is the Kinetic Energy formula?
KE = ½ × m × v². The kinetic energy of a moving object is half its mass times the square of its speed, so speed matters far more than mass.
How do I remember the Kinetic Energy formula?
Say it as 'half m v v'. The speed appears twice, so it is squared.
What should I watch out for in exams with Kinetic Energy?
Doubling the speed makes KE four times larger, while doubling the mass only doubles it. KE is never negative. The unit is the joule.

More Physics formulas

Ohm's Law

V = I × R

The current through a conductor is directly proportional to the voltage across it, as long as its resistance and temperature stay constant.

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Newton's Second Law

F = m × a

The net force on an object equals its mass multiplied by its acceleration, so the same push speeds up a lighter object more than a heavier one.

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First Equation of Motion

v = u + at

The final velocity equals the initial velocity plus the acceleration multiplied by the time, for straight-line motion with constant acceleration.

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