Resource 4: Summary of forces for the teacher
Background information / subject knowledge for teacher
- Forces are pushes and pulls.
- A force has two characteristics: size and direction.
- When forces act, they can change the shape of the things they act on. There is a bigger change from a bigger force.
- We can use the change to provide a quantitative measure of forces.
- Forces can be measured using a spring balance or force meter (newtonmeter) in units called newtons.
- An object’s weight is the force of gravity acting on it, thus weight is a force.
- The mass of an object is a measure of the amount of matter in it. It is constant and does not change.
- All objects exert a force on each other: the size of the force depends upon their masses.
- Gravity is the force that holds you down to the planet Earth.
- The force of gravity is smaller on the moon than on Earth because there is less matter in the moon (smaller mass) than in the Earth.
- On the Earth, every kilogram is pulled by gravity with a force of around 10 newtons towards the centre of the Earth.
- There is a distinction between mass and weight. Mass is an intrinsic property of an object – no matter where you are, you always have the same mass. Your weight is the gravitational force that acts on you. Your weight acts downwards, towards the centre of the Earth.
- Mass and weight have different units. Mass is measured in grams and kilograms, whereas weight (a force) is measured in newtons.
- Friction is a force that resists movement.
- A force is needed to start something moving, speed it up, slow it down or change its direction.
- The bigger the force, the greater the acceleration (or deceleration) on a fixed mass.
- When no overall force is acting on an object, it will remain stationary or continue at a steady speed in a straight line.
Adapted from: Developing Subject Knowledge – Jane Devereux