Work, energy and power

What is mechanical work?

This is done only when the object is moving and it’s motion is influenced by the applied force.

What is work?

Work is the product of the force applied to a body and the distance through which force is applied.

This is a vector

What is the equation for work?

Work = force / displacement

= Newton (N) x metres (m)

Unit = 1Nm=1J

What is power?

The rate at which physical work is performed or the rate at which energy is expended.

What is the equation for power?

Power = work / time

Power = force x displacement / time = force x velocity

What is energy?

It is the ability to do work.

The more energy a body has the greater the force with which it can move something.

What is GPE?

The capacity to work because of the position.

This increases with the more work done to overcome gravity

What is the calculation for potential energy?

Potential energy = mass x gravity x height

Gravity = 9.81

What is elastic potential energy?

Energy is stored as a result of applying force to deform an elastic object.

This energy is stored until force is removed and the object springs back to it’s original shape.

What’s the calculation for elastic potential energy?

EPE (J) = ½ x spring constant (N/m) x extension (m)²

What is kinetic energy?

The energy a body or object has because of its motion, the ability of the body to do work by virtue of its motion.

What’s the equation for kinetic energy?

KE= ½ x mass x velocity²

What’s the stress-strain relationship?

Hooke’s law says if you apply a force to a spring then the force stretches the spring in the direct proportion to the force.

This only applies to a limit which is unique to the material being deformed, soon after the material no longer exhibits elasticity with further elongation but will start to rupture.

What is the calculation for total energy?

Total energy = KE + PE

What is the coefficient of restitution?

the ratio of the final velocity to the initial velocity between two objects after their collision.

Can be between 0 and 1 and is the proportion of the total energy that remains in the object after the collision.

Coefficient results are

0 means all energy is transferred during collision.

1 means all energy is retained.

What are the coefficient of restitution equations?

If only one object was moving = e= V after/ V before

or

If more = e= √ h after / h before