Physics 3.4

Materials

What is extension of a spring?

Tensile forces act away from the centre the of the spring in both directions

What happens when compressive forces act towards the centre of the spring in both directions?

Spring undergoes compressive deformation

What is hooke's law?

For a material within its elastic limit, the force applied is directly proportional to the extension of the material

What is elastic deformation?

A spring will return to its original shape when the force is removed

What is inelastic/plastic deformation?

A spring won’t return to its original shape when the force is removed

How can we calculate force constant in series?

1/k1 + 1/k2 + 1/k3 = 1/ktotal

How can we calculate force constant with springs in parallel?

Ktotal = k1 + k2 + kn

What is the equation for elastic potential energy?

E = ½ x k x e²

What is tensile stress?

The force applied to a material per unit cross sectional area

What is the equation for stress?

Stress = f/a

What is tensile strain?

The extension or compression of a material per unit of its original length

What is the equation for strain?

Strain = x/L

What is the young modulus?

The ratio of stress to strain. A measure of the stiffness of the material

What is the equation for young modulus?

E = stress / strain

What energy changes occur during plastic deformation?

• material is stretched

• energy from work done is used to break bonds between molecules

• causes permanent deformation

what is breaking stress?

amount of stress a material can take without breaking

what is meant by brittle material?

• doesnt extend much when force is applied

• material breaks rather than stretches

what is the elastic limit?

• the limit of proportionality

• the point after which elastic deformation occurs

what does the area under a force extension graph represent?

energy stored in the material