What is Kinetic Energy? | Definition, Types, Formula & Examples

What is kinetic energy?

Kinetic energy is the energy that an object possesses due to its motion. As long as an object is moving at the same speed, it will maintain the same kinetic energy.

The kinetic energy of an object is calculated from the speed and mass of the object. As you can see from the equation below, velocity is squared and can have a significant effect on kinetic energy. Below we have provided the equation for kinetic energy (KE):

KE = 1/2 * m * v2

where m = mass and v = velocity

How to Measure Kinetic Energy

The standard unit of kinetic energy is the joule (J). Joule is the standard unit for energy in general. Other energy units include newton meter (Nm) and kilogram meter squared per second squared (kg m2/s2).

Kinetic energy is a scalar quantity, which means it has only magnitude but no direction. It is not a vector.

How is it different from Potential Energy?

Kinetic energy is due to the motion of an object while potential energy is due to the position or state of the object. When calculating the kinetic energy of an object, its speed is an important factor. However, speed has nothing to do with an object’s potential energy.

Example Using A Roller Coaster

One way to think about potential and kinetic energy is to imagine a car on a roller coaster. When the car rides on the roller coaster, it gains potential energy. It has the most potential energy at the top of the roller coaster. As the car goes down the roller coaster, it gains speed and kinetic energy.

At the same time, it gains kinetic energy, loses potential energy. At the bottom of a roller coaster, cars have the highest speed and greatest kinetic energy, but also the least potential energy.

Example problems:

1. If a car and a bicycle are moving at the same speed, which car has more kinetic energy?

The car does this because it has more mass.

2. If a ball weighs about 1 kg and is moving with a speed of 20 meters per second, what is its kinetic energy?

KE = 1/2 * m * v2
KE = 1/2 * 1kg * (20m /s)2
KE = 200J

3. A boy weighing 50 kg and running 3 meters per second, what is his kinetic energy?

KE = 1/2 * m * v2
KE = 1/2 * 50 g * (3m/s)2
KE = 225J

Interesting Facts about Kinetic Energy

If you double the mass of an object, you double the kinetic energy.

If the speed of an object is doubled, the kinetic energy will increase by 4 times.

The word “kinetic” comes from the Greek word “kinesis” which means movement. Kinetic energy can be transferred from one object to another in the form of collisions.

The term “kinetic energy” was coined by the mathematician and physicist Lord Kelvin.