Elasticity

Objectives

• Elasticity

• Hooke’s Law

• Stress

• Strain

• Young modulus

• Elasticity :

• is a property of object to deform when a force is applied and to return it’s original shape when the deforming force is removed,

• e.g. rubber band, spring

• Plastic Deformation • when the deforming force is removed, the object doesn’t return to it’s

original shape

• e.g. Plastine, Blu-tack

• Hooke’s law:

‘The extension of a body is proportional to the force causing it provided that the limit of proportionality is not exceeded’

Extension:

when a force is applied it changes the length of the object the change in length is called extension

Limit of proportionality :

The greatest force that can be applied to an elastic body without causing permanent deformation.

• Force (y axis)

• Extension (x axis)

• Stress:

is a quantity that is proportional to the force causing a deformation. Stress is the external force acting on an object per unit cross sectional area.

Stress is the load per unit cross-sectional area of the material

Stress (Nm-2) = force (N)

cross-sectional area (m2)

• Strain:

is the ratio of extension to original length.

Strain = extension (m)

original length (m)

There isn’t any unit of strain.

• Young modulus :

the ratio of stress to strain.

Young Modulus (Nm-2) = stress

strain

or E = stress

strain

Questions….

Thanks……