1Pushes and pulls
A force is a push or a pull. Pushing a box moves it away from you; pulling on a rope drags a sledge towards you.
force
Lesson 3.1 notes
Forces and force arrows
Pushes and pulls between two objects, contact and non-contact forces, newtons and force arrows.
2What forces do
Forces can start things moving, speed them up, slow them down, change their direction or change their shape.
3Always two objects
A force always acts between two objects. When one skater pushes the other, the other pushes back on her, so they both glide apart.
4Contact forces
Contact forces act when objects touch: a push or a pull, friction, air resistance, and the support force from a surface.
contact force
5Non-contact forces
Non-contact forces act across a gap, without the objects touching: gravity, the force between magnets, and static electricity.
non-contact force
6Newtons
Forces are measured in newtons (N) with a newton meter, which has a spring inside. An apple weighs about 1 N; a 1 kg bag of sugar weighs about 10 N.
newtonnewton meter
7Force arrows
A force arrow starts on the object and points the way the force acts. Its length shows the size: twice the force, twice as long.
force arrow
Explore: Newton meter
Hang different things on a newton meter and read their weight in newtons. Then take them to the Moon and see what changes.
Common mistake: A force always acts between two objects
Nothing has a force stored inside it. Your foot pushes the ball, the Earth pulls the ball down and the ground pushes it up. Every force is one object pushing or pulling on another.
Remember
- A force is a push or a pull between two objects. Forces are measured in newtons (N).
- Contact forces act when objects touch. Non-contact forces, such as gravity, magnetism and static electricity, act across a gap.
- A force arrow starts on the object the force acts on and points the way the force acts. Its length shows the size of the force.
Going further at GCSE