What things could a force do to an object?
Forces can make things:
- Speed up
- Slow down
- Change direction
- Change shape
Do forces have just size, just direction, or size and direction?
Forces have size and direction.
On a diagram, what can we use to show a force?
On a diagram you can use an arrow to show a force.
The length of the arrow shows the size of the force, and the direction the arrow is pointing shows the direction the force will act.
What is meant by a contact force?
A contact force is one in which objects are touching. For example, kicking a ball, or friction.
What is meant by a non-contact force?
A non-contact force is one where the objects are not touching. For example, magnetism and gravity.
What is friction?
Friction is a force that slows things down. It always opposes movement.
What can you use to reduce friction?
To reduce friction, you can use lubrication. for example, oil on a bike chain.
What is meant by balanced forces?
Balanced forces are forces which cancel each other out, so there is no change in movement.
What is the name of the force labelled X?
The force labelled X is the weight.
What is the name of the force labelled Y?
The force labelled Y is drag or friction.
If the force from the engine is bigger than force Y, what happens to the boat?
If the force from the engine is bigger than force Y then the boat will speed up or accelerate.
What can you say about the size of force X compared to the upthrust?
The forces are balanced, so force X (the weight) must be equal to the upthrust.
What is meant by pressure?
Pressure is a measurement of how spread out a force is.
Explain, using ideas about pressure, why wading birds have webbed feet.
Wading birds have webbed feet because they need to walk on mud without sinking. The webbed feet have a large area meaning the force is spread out and the pressure is less. This stops them sinking in.
What units is pressure measure in?
Pressure is measured in Pascals or Newtons per metre squared.
Calculate the pressure when a boy of weight of 400 N sits on a chair with an area of 0.25 m2.
Use the formula:
Pressure = force / area
= 400 / 0.25
= 1600 N/m2
What causes air resistance?
Air resistance is caused by friction between the air particles and the moving object.
What happens to air resistance if you are travelling faster?
If you are travelling faster, air resistance increases.
Why do mountain bikes have wide tyres?
Mountain bikes have wide tyres:
- to increase friction (and stop you sliding around)
- to decrease the pressure (spread the force over a large area so that you don't sink in to the mud)
What is the formula to calculate pressure?