Physics P1 - Bulk Properties of solids

What is density?

It is the mass per unit volume of an object.

What is Hooke's law?

It is the law that states that extension is directly proportional to the force applied, as long as external conditions are kept constant.

What is the force-extension graph for hooke's law?

Straight line through the origin.

What is the limit of proportionality?

It is the point after which hooke's law is no longer obeyed.

What is the elastic limit?

It is the point just after the limit of proportionality and if you increase the force applied beyond this, the material will deform plastically.

What does plastically mean?

Permanently stretched.

What is the equation of hooke's law?

Force = spring constant * extension

What is tensile stress?

Force applied per unit cross sectional area.

What is the tensile strain?

Caused by tensile stress, it is the extension per unit original length.

What is the equation for tensile stress?

force/area

What is the equation for tensile strain?

Strain = extension / original length

What is the work done when making a material stretch or compressed called?

Elastic strain energy.

What is the equation for elastic strain energy?

Energy = 1/2 x force x extension

What is breaking stress?

It is the value of stress at which the material will break apart. This changes depending on external conditions.

What is plastic behaviour?

This is where an material will experience a large amount of extension as the load is increased, especially beyond the elastic limit.

What is brittle behaviour?

This is where a material will extend very little, and therefore is likely to fracture with a low extension.

What are the loading and unloading lines of a graph?

Parallel.

What happens when a materials stretch is elastic?

It will return to its original form.

What happens when a material stretch is plastic?

Work done is done to move atoms apart, so energy is not stored as elastic strain energy but is dissipated as heat.

How is plastic behaviour used in context?

- Car crumple zones
- Seat belts

What do stress-strain graphs describe?

The behaviour of a material.

What is the ultimate tensile stress?

This is the highest point on the graph which shows the maximum stress the material can withstand.

What is Young's modulus?

This is what describes the stiffness of a material.

What is the equation for Young's Modulus?

Stress / Strain.

What is the gradient of a stress-strain graph equal to?

Young's Modulus.