What a force is, contact and non-contact forces, scalars and vectors, and weight W = mg with gravitational field strength and centre of mass.
What you will learn
- Sort quantities into scalars and vectors
- Name contact and non-contact forces
- Use W = mg, including masses in grams
- Explain the difference between mass and weight
Pushes and pulls with a direction
A force is a push or a pull on an object, caused by it interacting with something else.
Forces are measured in newtons (N).
Every force has a size and a direction, so force is a vector. A quantity with a size only is a scalar.
- Vectors: force, weight, velocity (speed in a given direction), displacement, acceleration (how fast the velocity changes), momentum (mass × velocity). Later units teach each one.
- Scalars: mass, speed, distance, time, energy, temperature.
On a diagram a vector is an arrow: its length shows the size, and it points in the direction of the force.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Pushes and pulls with a direction
- Touching or not
- Weight is a force
- Centre of mass
- Try it: Your first weight
9 practice questions, marked as you go; about 20 minutes in all.
Key terms
Vector, Scalar, Contact forces, Non-contact forces, Gravitational field strength, Centre of mass
In this unit: Forces, work, elasticity, moments and pressure
Weight and resultant forces, work done, stretching springs and their required practical, moments, levers and gears, and pressure in fluids.