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# Kinetic Energy Concerns Movement of Matter

by Ron Kurtus (revised 9 October 2014)

A moving object is said to have kinetic energy that can be transferred to another object. The motion can be translational (in a straight or curved line), according to the equation KE = ½ mv². This equation is valid provided that the speed of the object does not approach the speed of light.

Kinetic energy can also be rotational about an axis or as a vibration.

Motion and kinetic energy can be a direct result of a force can be applied to a object. Also, releasing potential energy can create kinetic energy, such as with springs and chemical reactions. Most forms of energy where material is moving are kinetic energy.

Questions you may have include:

• What does the equation KE = ½ mv² mean?
• How can a force create kinetic energy?
• What are other forms of energy?

This lesson will answer those questions. Useful tool: Units Conversion

## Translational kinetic energy

Most of the kinetic energy you see is translational—meaning that the object moves in a straight or curved line. The equation for translational kinetic energy is:

KE = mv2/2

where

• KE is the kinetic energy, usually measured in joules
• m is the mass of the object, usually measured in kilograms
• v is its speed or velocity of the object, measured in meters per second
• v2 is the velocity squared or v times v

### Can transfer energy

When a moving object collides with another object, some of its KE can be transferred according to the Law of Conservation of Energy and Law of Conservation of Momentum.

### Scale a KE

Kinetic energy covers a wide range of scales. A moving subatomic particle has KE, according to its mass and velocity. Likewise, a moving truck has its own KE.

## Rotational kinetic energy

An object or particle that is rotating has kinetic energy that can be transferred to another object.

KErot = Iω2/2

where

• KErot is the rotational kinetic energy, measured in joules (J)
• I is the moment of inertia in kg-m2
• ω is the angular velocity in radians per second (rad/s)

The moment of inertia of an object depends on the distribution of its mass. Thus, there is no simple calculation of I.

### Can transfer energy

When a spinning object comes in contact with another object, some of its KE can be transferred by friction or other resistive force.

### Scale a KE

On the macro scale, an object that comes into contact with a spinning wheel can be projected forward.

On the micro scale, a rotating molecule can affect others through electromagnetic forces.

## Vibrational kinetic energy

An object that is vibrating or oscillating has kinetic energy that can be transferred to another object.

## Summary

Kinetic energy is the energy of a moving object according to the equation KE = ½ mv². Motion and kinetic energy can be a direct result of a force can be applied to a object. Releasing potential energy can create kinetic energy, such as with springs and chemical reactions. Heat, electrical energy and light are forms of kinetic energy.

Move with kinetic energy

## Resources and references

Ron Kurtus' Credentials

### Websites

Physics Resources

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