Transcript Hooke’s Law - Tasker Milward Physics Website

IP2.11.5 Hooke’s Law
Hooke’s Law
© Oxford University Press 2011
IP2.11.5 Hooke’s Law
In 1676 the British scientist
Robert Hooke investigated the
relation between the force
applied to an elastic object and
the change in its length (called
the extension).
© Oxford University Press 2011
IP2.11.5 Hooke’s Law
 He found the force applied to an object was
directly proportional to its extension, up to a
certain point.
 When he doubled the force on a spring he found
the extension would also double. If applying 20 N
caused a spring to extend 0.5 m then applying
40 N would cause it to extend 1.0 m.
 This relationship continues up to the limit of
proportionality. Above this point the spring
starts to deform – it will no longer return to its
original length.
© Oxford University Press 2011
IP2.11.5 Hooke’s Law
Can you think of an application that uses this relationship?
A newtonmeter or weighing
scales use this relationship.
The force of gravity caused by
an object’s mass (its weight)
can be measured by using the
extension of a spring. The
spring has to calibrated first for
a known weight and then other
weights can be measured.
Before Hooke discovered this
relationship weighing had to be
done using a balance, with known
weights used on one side to balance
the weight of the object you were
weighing.
© Oxford University Press 2011
IP2.11.5 Hooke’s Law
 How much a certain spring extends depends on the force applied and the
spring constant.
 This is a measure of the stiffness of the spring and it is measured in
newtons per metre (N/m).
 The higher the spring constant the stiffer the spring and the less it extends
for a given force.
© Oxford University Press 2011
IP2.11.5 Hooke’s Law
The relationship between force, spring constant
and extension is represented in this equation.
force = spring constant  extension
(newtons, N) (newtons per metre, N/m) (metres, m)
If the force is called F, the spring constant k and
the extension e, then
F=ke
© Oxford University Press 2011