Kinetic energy

Kinetic energy is energy found in moving objects. Any object that is in motion has kinetic energy. The faster the object is travelling, the more kinetic energy it has. The slower the object is travelling, the less kinetic energy it has.

Kinetic energy can be expressed using the following equation:

KE = mv²

where m is mass in kilograms (kg) and v is velocity in metres per second (m/s). KE is kinetic energy measured in joules (J), which is equivalent to a newton applied over a metre.

Using this equation, we can see that both the mass and the speed of an object affect its kinetic energy. This can be seen easily by imagining the damage done by a toy car and a full-sized car running into a brick wall. A toy car running into a wall will do little damage (and therefore only a little work), but a full-sized car will do considerable damage (and therefore a lot of work).

See Image 1

When the speed of an object increases, its kinetic energy increases exponentially. This means that if a car is travelling twice as fast, it has four times the kinetic energy. A car with a mass of 1500 kg travelling at 15 m/s has a kinetic energy of (1500 x 152) 2 = 168 750 J. The same car travelling at 30 m/s, however, has a kinetic energy of (1500 x 302) 2 = 675 000 J, which is four times as much.

Work done by kinetic energy can change the velocity or shape of another object. Imagine a billiard table with two balls on it, one black and one white. The white billiard ball travels towards the black one. When the white ball hits the black ball, it causes the black ball to start moving. In this case, the object has done work with its kinetic energy by altering the velocity of another object. This will also alter the velocity of the white ball, however. If the white ball transfers all of its kinetic energy to the black ball, the white ball will stop moving.

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Work done by kinetic energy can also alter the shape of another object. Imagine a car accident. If the two cars were travelling very quickly, they would do work on each other with their kinetic energy to crumple the cars. If the two cars were travelling more slowly, they would not do as much work and therefore would not do as much damage.

See Image 3