What type of force is being experienced in each picture?
Fig. 17.3.2 Forces are exerted in pairs when a person jumps off the ground
Forces in Pairs
Think about the forces being applied when the boy jumps off the ground in Fig. 17.3.2.
z The boy pushes the ground down: this is the force the boy exerts on the ground.
z The ground pushes the boy up: this is the force the ground exerts on the boy. These forces happen in a pair. This is known as an interaction pair.
Describing the interaction pair
There is a second interaction pair happening when the boy jumps. Copy the following sentences and circle the correct word to describe this second interaction pair:
z Gravity pulls the boy (up/down). This is the force of the (Earth/boy) on the (Earth/boy). z The boy pulls the Earth (up/down). This is the force of the (Earth/boy) on the (Earth/boy).
What happens next?
Two ice skaters place their hands together and ice skater A pushes on ice skater B. Predict what will happen to ice skater B when ice skater A pushes. Explain why you made this prediction.
Measuring Forces
Forces can be measured in the laboratory using a newton meter. This is also known as a spring balance. Forces can also be measured digitally using a force meter.
Remember, the SI unit for force is the newton (N). Taking readings
A student applies a pulling force and measures it with a newton meter. What is the value of this force?
Fig. 17.3.4 Fig. 17.3.3 A newton meter being pulled 291
