Contact and non-contact forces
Contact forces
Force exerted between two objects when they are touching. are A push or a pull. The unit of force is the newton (N). that act between two objects that are physically touching each other.
Non-contact forces
A force that affects an object without coming into contact with that object, eg magnetism. are forces that act between two objects that are not physically touching each other.
When the wind pushes against an umbrella, it can change the shape of the umbrella and/or the speed of the umbrella.
What happens depends on which direction the wind is blowing and how strongly it is blowing.
Learn more on scalar and vector quantities, contact and non-contact forces in this podcast
Listen to the full series on 大象传媒 Sounds.
A measurement that needs both a size and a direction to describe it is called a vector. Vector quantities have both The size of a physical quantity. and an associated direction.
Some examples of vector quantities include:
- force - 20 newtons (N) to the left
- velocity - 11 metres per second (m/s) upwards
- acceleration - 9.8 metres per second squared (m/s虏) downwards
The direction of a vector can be given in a written description, or drawn as an arrow. The length of an arrow represents the magnitude of the quantity. The diagrams show three examples of vectors, drawn to different scales.
A measurement that doesn't have a direction is called a scalar. Scalar quantities only have a magnitude or size.
Some examples of scalar quantities include:
- temperature - 10 degrees Celsius (掳C)
- mass - 5 kilograms (kg)
- energy - 2,000 joules (J)