Types of ForcesEdexcel GCSE Physics: Revision notes
Section 1
What is a force and how can objects interact?
A force is a push or pull that acts on an object as a result of its interaction with another object. Objects can interact in two ways:
- Contact forces: the objects are physically touching, e.g. normal contact force (a surface pushing back on an object resting on it) and friction (opposing relative motion between surfaces)
- Non-contact forces (action at a distance): the objects do not need to touch, acting through a field — including gravitational fields, electrostatic fields and magnetic fields
Forces always occur in interaction pairs: when object A exerts a force on object B, object B exerts an equal and opposite force back on object A.
Friction (contact) slows a sliding box; gravity (non-contact, gravitational field) pulls a falling object down without touching it.
Section 2
What is the difference between vector and scalar quantities?
- A scalar quantity has magnitude (size) only, e.g. speed, distance, mass, energy
- A vector quantity has both magnitude and direction, e.g. force, velocity, displacement, acceleration, momentum
Force is a vector, so it must always be described with both a size and a direction. Vectors can be represented by arrows: the length shows magnitude and the direction the arrow points shows the direction.
Section 3
How are forces resolved and combined? (Higher tier)
Several forces acting on an object can be combined into a single resultant force that has the same effect as all the forces acting together.
- Vector diagrams (scale drawings) can be used to add forces acting at different angles and find the resultant
- A single force can also be split (resolved) into two components acting at right angles to each other
- Equilibrium occurs when the resultant force on an object is zero — the object is either stationary or moving at constant velocity
- Free body force diagrams show only the object and the individual forces acting on it as labelled arrows, ignoring the objects causing those forces
When drawing a free body diagram, only include forces acting ON the object, not forces the object exerts on other things.
Section 4
How can unwanted energy transfer be reduced?
Friction between moving surfaces transfers energy away as heat, which is often unwanted (it wastes energy and wears out components). Lubrication — adding a substance such as oil or grease between surfaces — reduces friction by allowing the surfaces to slide past each other more easily, reducing unwanted energy transfer and wear.
Must Know
- Contact forces (e.g. friction, normal contact force) need touching objects; non-contact forces (gravitational, electrostatic, magnetic) act through fields
- Forces always occur in equal and opposite interaction pairs
- Scalars have magnitude only; vectors have magnitude and direction
- Force is a vector quantity
- Resultant force = combined effect of all forces acting on an object (higher tier)
- Equilibrium means the resultant force is zero (higher tier)
- Lubrication reduces unwanted energy transfer due to friction
That's the notes covered.
Carry on to the next subtopic.