The City School
Handout Number: 2.11.1,2,3 Science
Topic: Forces and Motion
Name: ___________________ Class: ___________
Learners will be able to:
2.11.1 Identify and describe different types of forces associated with deforming objects; stretching and squashing- springs.
2.11.2 Investigate how forces can cause changes in the shape of materials, including springs.
2.11.3 Demonstrate the linear force-extension relationship and recognize Hooke’s Law as a special case
Recall:
Forces happen when there is an interaction between objects.
We feel forces as either a push or a pull.
You can ‘push’ open a door.
You can ‘pull’ a sleigh.
We feel forces as pairs that act in opposite directions.
Forces can be measured using a Newton metre, which is sometimes called a force metre or spring balance.
Representing forces
• Forces are measured in Newtons (N).
• We can represent a force with an arrow.
• The way the arrowhead points represents the direction of the force.
• The size of the arrow represents the magnitude of the force.
Deformation:
Some materials can be stretched and squashed if they have elastic
properties. If an object changes shape, this is called deformation.
Stretching
Some objects are able to change shape by stretching.
If an object can stretch, we can measure its extension because it will be longer.
If we stretch an object, we must do work or transfer energy to stretch it.
If an object is stretched, it will have tension.
If an object is stretched, it is deformed.
Squashing
Squashing an object will also lead to deformation.
When we squash an object, it will be shorter.
When an object is squashed by a force, we say it has been compressed.
Deformation
Sometimes, objects do not return to their original shape after they have been
squashed or stretched. This is called inelastic deformation.
When objects return to their original shape, we call this elastic deformation.
The more force you apply to an object, the more it will be deformed.
Resultant forces
The resultant force is the overall force.
If two forces are acting in the same direction, the resultant force is the sum of all the forces.
If two forces are acting in opposite directions, the resultant force is the difference between the forces.
Hooke’s law:
Deformation
Deformation occurs when we apply a force to an object to change its shape. Applying a force to an object can
cause it to either:
• stretch - the object increases in length
• compress - the object decreases in length
In general, the greater the force applied, the more deformed an object will become.
However, not all materials behave in the same way. Elastic materials will return to their original shape once
the force is removed, whereas inelastic materials will change shape permanently and may even break.
Hooke's law
When you apply a force to a material it can extend. The extension is the amount the length has increased by.
Remember that to calculate the force applied to the spring due to the
weight of the mass, you need to convert the mass in grams into kilograms
(divide by 1000) and then multiply this mass by the gravitational field
strength (10 N/kg), using this equation:
Figure 1 When the dependent variable is
directly proportional to the independent
variable, the graph will have a straight line
that goes through the origin (0,0).
In the context of Hooke's Law, the force applied to a spring (x-axis) and its extension (y-axis) shows a linear
relationship within the elastic limit. The graph is a straight line through the origin, indicating that the extension
is proportional to the force applied.
If you keep loading more and more on, the spring will
not return to its original length when you remove the
force. It has reached its limit, called the elastic limit.
The spring cannot spring back and it is permanently
extended.
Elastic materials break if the force applied to them is
too large.
