1.1.2Forces and Their Effects
Contact and Non-Contact Forces — Oxford AQA International GCSE Combined Science - Physics Revision Notes & Topical Questions
5 min read 6 parts Lesson 3 of 16
Section 1 of 6What a force does
Definition
- Definition A force is a push or a pull on an object, caused by an interaction with another object.
- It is measured in newtons (N).
Change speed
- Change speed A force can make an object speed up or slow down, for example the thrust of a car engine.
Change direction
- Change direction A force can alter the direction of motion, such as the pull of gravity bending the path of a comet.
Change shape
- Change shape A force can stretch, squash or bend an object, such as a heavy load compressing or extending a spring.
Section 2 of 6Important forces and their names
| Force | Description |
|---|---|
| Weight | The force of gravity acting on a mass |
| Thrust | A force that drives an object forwards, such as from a rocket engine |
| Air resistance (drag) | Friction between a moving object and the air |
| Upthrust | The upward push of a fluid on an object placed in it |
| Tension | A pulling force carried along a rope, string or cable |
| Compression | Forces that squeeze an object inwards |
| Reaction (normal) force | The force from a surface pushing back on an object resting on it |
| Electrostatic force | The force between charged objects |
Section 3 of 6Contact forces
Objects physically touching
Friction
- Friction Acts where surfaces rub together and opposes the motion.
Air resistance
- Air resistance A type of friction as an object moves through air.
Tension
- Tension Appears in a string or rope when it is pulled at both ends.
Reaction force
- Reaction force A supporting surface pushes the touching object away from it, at right angles to the surface.
Section 4 of 6Non-contact forces
Acts through a field
- Acts through a field These forces act at a distance with no touching, because of a gravitational, electric or magnetic field.
Gravitational force
- Gravitational force An attraction between any two objects with mass, such as a planet and a comet.
Electrostatic force
- Electrostatic force A force on charged objects; like charges repel and unlike charges attract.
Magnetic force
- Magnetic force A force between magnets, or on magnetic materials, that acts without touching.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Force | A push or pull on an object caused by an interaction, measured in newtons. |
| Contact force | A force that acts between objects that are physically touching. |
| Non-contact force | A force that acts at a distance through a field, without the objects touching. |
| Weight | The gravitational force on an object, which acts towards the centre of the Earth. |
| Field | A region in which an object experiences a force at a distance, such as a gravitational field. |
Section 6 of 6Exam technique
1
Listing weight as a contact force; weight is gravity acting at a distance, so it is non-contact.
2
Saying friction always makes things stop; it opposes motion but can also let you walk or grip.
3
Treating the reaction force as upwards only; it acts at 90 degrees to the surface.
4
Mixing up thrust and upthrustthrust drives an object forward, upthrust is the upward push of a fluid.
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