Work Done & Deformation & Hooke's Law

When is work done by a force?

When a force causes an object to move through a distance along the force's line of action.

What is the unit of work done?

Joules (J).

What is one joule?

The work done when a force of 1 N causes a displacement of 1 m along its line of action.

What happens to energy when work is done?

Energy is transferred between stores.

What happens when work is done against friction?

Energy is transferred to thermal energy stores, increasing the temperature of the objects and surroundings.

What is deformation?

A change in the shape of an object caused by forces.

What is elastic deformation?

The object returns to its original shape when the forces are removed.

What is inelastic deformation?

The object does not return completely to its original shape when the forces are removed.

Why are at least two forces needed to change the shape of a stationary object?

Forces must act on different parts of the object to stretch, compress or bend it while it remains stationary.

Give three examples of deformation.

Stretching, compression and bending.

State Hooke's law.

Extension is directly proportional to applied force, provided the limit of proportionality is not exceeded.

What is the spring constant?

A measure of the stiffness of a spring.

What does a larger spring constant mean?

A greater force is required to produce the same extension.

What is extension?

The increase in length of a spring compared with its original length.

What is the limit of proportionality?

The point beyond which extension is no longer directly proportional to applied force.

Does exceeding the limit of proportionality necessarily mean permanent deformation?

No, the limit of proportionality and the elastic limit are not necessarily the same.

What happens after a spring's elastic limit is exceeded?

It becomes permanently deformed and does not return completely to its original length.