Kinetic Energy
The energy of motion — how mass and speed combine to determine how much energy a moving object carries.
Kinetic Energy = Energy of Motion
Any object that is moving has kinetic energy. The faster it moves, or the more massive it is, the more kinetic energy it carries. A parked car has zero kinetic energy. That same car at highway speed has enormous kinetic energy.
Memory trick: Think of KE as "half the mass times speed-squared." The two things that matter are how heavy the object is and how fast it's going — but speed matters twice as much because it's squared.
- A rolling bowling ball
- A flying airplane
- Water flowing in a river
- A thrown baseball
- A rock perched on a cliff
- A stretched rubber band
- Water behind a dam
- A coiled spring
Key Points to Remember
Kinetic energy is the energy of motion — any moving object has it.
Formula: KE = ½ × m × v² — mass in kg, velocity in m/s, KE in Joules.
Velocity is squared — doubling speed quadruples kinetic energy.
KE can be transferred to other objects or converted to heat, sound, or light.
Kinetic energy and potential energy together make up an object's total mechanical energy.
Try the Formula Yourself
Enter any mass and velocity to calculate kinetic energy. The calculator shows you the step-by-step work so you can see exactly how the formula is applied.
KE = ½ × 1,000 × 20² = ½ × 1,000 × 400 = 200,000 Joules (200 kJ)
Now double the speed to 40 m/s:
KE = ½ × 1,000 × 40² = ½ × 1,000 × 1,600 = 800,000 Joules (800 kJ)
🔑 Doubling speed (20→40 m/s) quadrupled KE (200,000→800,000 J). This is why speed limits save lives.
KE = ½ × 0.45 × 30² = ½ × 0.45 × 900 = 202.5 Joules
🔑 A relatively light ball moving fast still carries significant kinetic energy — enough to be felt on impact.
KE = ½ × 1,200 × 0² = ½ × 1,200 × 0 = 0 Joules
🔑 No motion = no kinetic energy. A stationary object, no matter how massive, has zero KE. It may have potential energy, but not kinetic.