• Hooke’s Law
• 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
• 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’
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 ca
using permanent deformation.
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) =
cross-sectional area (m2)
is the ratio of extension to original length.
original length (m)
There isn’t any unit of strain.
• Young modulus :
the ratio of stress to strain.
Young Modulus (Nm-2) = stress
E = stress