Anything that moves has kinetic energy. A rolling ball, a speeding car, a flying arrow, a walking person. Kinetic energy is the energy of motion, and it depends on both mass and speed. The formula is KE = ½mv². Mass matters, but speed matters more. Double the mass and you double the kinetic energy. Double the speed and you quadruple it. That is why a car crash at 60 mph is four times as destructive as a crash at 30 mph, not twice.

Kinetic energy is a scalar quantity, meaning it has magnitude but no direction. It is always positive or zero. A moving object has kinetic energy regardless of which way it is moving. Kinetic energy can be transferred between objects. In a collision, one object can transfer kinetic energy to another. It can also be converted into other forms of energy. When a car brakes, kinetic energy becomes thermal energy in the brake pads. When a ball hits the ground and bounces, some kinetic energy becomes sound and heat. Kinetic energy is one of the two main forms of mechanical energy, along with potential energy.

Kinetic energy facts

• Definition. Energy of motion.
• Formula. KE = ½mv².
• Depends on. Mass and speed.
• Speed matters more. Doubling speed quadruples KE.
• Scalar. No direction.

Kinetic energy is not the same as momentum. Momentum is mass times velocity and is a vector. Kinetic energy is a scalar and depends on the square of speed.