Page 135 - Science Coursebook

9.7 The turning effect of a force

Weighing with scales
The photograph shows a type of balance
which has a pivot at the middle. A beam is
balanced at the pivot.
pivot
The balance is being used to weigh apples.
The apples are placed on the right. The weights weight of
weights on the left provide the force needed turn scales apples
to balance the weight of the apples. anticlockwise turn scales
clockwise
You can see that the weights are slightly
heavier than the apples.
The weights cause the balance to tip Which are heavier, the apples or the weights?
downwards on the left, so that the beam
turns anticlockwise.
The apples cause the balance to tip
downwards on the right. This would make
the beam turn clockwise, but the turning
effect of the weights is greater.

Question
2 a How can you tell from the photograph that the
weights are heavier than the apples?
b Draw a diagram to show the forces on the balance.

Activity 9.7

Scale maker
You can make your own simple scales using a piece
of wood balanced on a pivot made from a wooden
rod.
Part 1: Your teacher will give you a number of
items. Use your scales to compare the different items

and put them in order, from lightest to heaviest.
Part 2: Your teacher will give you a single 1 N
weight. Find out which of your items are heavier
than 1 N, and which are lighter.

Part 3: Can you think of a way to use your scales to

find the weight of each item?

Summary
• A force has a turning effect when it causes an object to turn

about a pivot.

9 Forces in action 133