Elasticity
1 of 14
© Boardworks Ltd 2012
2 of 14
© Boardworks Ltd 2012
Changing shapes
Forces can make objects change their speed or their
direction when they are in motion. They can also make
objects change shape.
Stretching forces can change the shape of
objects, making them longer and thinner.
Compression forces
can squash objects,
making them smaller.
3 of 14
© Boardworks Ltd 2012
Elastic or plastic?
In physics, materials are described as having either
elastic or plastic properties. Most materials display both
properties, depending on how much they are deformed.
Plastic materials change shape
permanently when they are
deformed by an external force.
Elastic materials return to
their original shape once
the external force is removed.
4 of 14
© Boardworks Ltd 2012
Elastic potential energy
A stretched or compressed material,
like the spring in a jack-in-the-box when
the lid is closed, has elastic potential
energy (EPE) stored in it.
EPE is the energy stored in a body
due to a load causing a deformation.
According to the law of conservation of energy,
no energy is created or destroyed when a spring
is compressed. Therefore the work done in compressing
the spring is equal to the EPE stored in it, plus any
energy released as heat and sound.
5 of 14
© Boardworks Ltd 2012
Slingshot science
6 of 14
© Boardworks Ltd 2012
Investigating springs
7 of 14
© Boardworks Ltd 2012
Results
plastic region
force (N)
break point
limit of
proportionality
elastic limit
elastic region
extension (cm)
If a spring is stretched far enough, it reaches the limit of
proportionality and then the elastic limit.
The elastic limit is a point beyond which the spring will no
longer return to its original shape when the force is removed.
8 of 14
© Boardworks Ltd 2012
Hooke’s law
The limit of proportionality is a point beyond which behaviour
of an elastic material no longer conforms to Hooke’s law:
The extension of a spring is directly
proportional to the force applied, provided
its limit of proportionality is not exceeded.
F e
or
F = ke
original length
where k is a constant.
x
F
9 of 14
© Boardworks Ltd 2012
Elasticity calculations
10 of 14
© Boardworks Ltd 2012
11 of 14
© Boardworks Ltd 2012
Glossary
12 of 14
© Boardworks Ltd 2012
Anagrams
13 of 14
© Boardworks Ltd 2012
Multiple-choice quiz
14 of 14
© Boardworks Ltd 2012