Good Science Victorian Curriculum Year 7

CHAPTER 8: FORCES
2
We can predict how forces will affect
motion
When the forces acting on an object are unbalanced, that object’s
motion will change. If you look at how the forces are unbalanced,
you can describe how the motion of the object will change.
It’s easy to predict how a stationary object such as a basketball will
move when you apply a force to it, such as by throwing. A force acting
in the opposite direction to an object’s movement is also fairly easy
to predict. For example, a rolling ball on a flat floor will slow down
and eventually stop due to friction.
INVESTIGATION 8.2
Blowball
KEY SKILL
Identifying and
managing relevant
risks
Go to page 176
How can you explain the change
in motion of an object?
CHECKPOINT 8.2
3
Forces can be added
up to work out
their effect
It is easy to predict the motion
of an object when only a single
force is acting on it. But when
many forces act on an
object, adding them up is
the best way of working
out how it will behave.
Normal force
Force of throw
1 What are the possible results
of unbalanced forces acting
on an object?
2 What are the three ways that
unbalanced forces can change
an object’s motion?
3 What are two ways that
the overall forces acting
on an object can become
unbalanced?
4 An object with a force acting
on it in the opposite direction
to its motion will slow down.
Suggest why.
When you hold a
basketball, there are two
forces acting on it – the
force of gravity pulling it
down and the normal force
Force of gravity
from your hands holding it up.
These forces are balanced.
If you push a ball away from you to pass it,
you’re applying a third force to the ball. The
forces acting on it become unbalanced,
and the ball moves away from you.
In what direction does the ball move?
You can work this out by adding up the
forces acting on the ball. The force of
5 If a person is sitting on a bike
at the top of a hill, then slowly
rolls down the hill without
pedalling, describe the forces
acting on the bike and why the
rider doesn’t need to pedal.
6 Explain how you think the
size of the force applied to
an object affects its motion.
RESEARCH
7 Rockets require an extremely
large unbalanced force in
order to be launched into
space. Research how this
force is created.
gravity and the force from your hands
holding the ball cancel each other out,
leaving only the force from the push.
What happens when you unbalance
the forces on an object?
Figure 8.3
The applied force of
a throw unbalances
the forces acting on
a ball.
SUCCESS CRITERIA
I can explain what
unbalanced forces are.
I can draw a simple force
diagram with arrows
showing unbalanced forces.
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