Types of 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. Examples of contact forces include:
Normal contact forces
An object at rest on a surface exerts a force on the surface. The reaction force acts at right angles to the surface and is known as the normal contact force. For example, a book on a table.
Frictional forces
Objects moving across a surface exert force on the surface. The reaction force acts parallel to the surface and is known as a frictional force. For example, a box sliding down a slope.
Air resistance
An object moving through the air experiences a frictional force between the object and the air. This frictional force is known as A force of friction produced when an object moves through the air.. For example, a skydiver falling through the air.
When a contact force acts between two objects, both objects experience the same size force, but in opposite directions. This is Newton's third law of motion.
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Non-contact forces
The push or pull acting between objects that are not physically touching when they interact. are forces that act between two objects that are not physically touching each other. Examples of non-contact forces include:
Magnetic force
A magnetic force is experienced by any Able to be magnetised or attracted to a magnet. material in a Area surrounding a magnet that can exert a force on magnetic materials..The magnetic material does not need to be another magnet. For example, both iron and steel are magnetic materials.
Opposite magnetic poles (N–S or S–N) Objects that tend to move together because of a force between them attract each other. each other:
Like magnetic poles (N–N or S–S) Objects that tend to push apart because of a force between them repel each other. each other:
Electrostatic force
An A force of attraction between particles with opposite charges. is experienced by any Particles, usually ions or electrons, that carry electrical charges. in an Area surrounding an electric charge that may influence other charged particles..
Opposite charges (+ and –) attract:
Like charges (– and –, or + and +) repel:
Gravitational force
A gravitational force is experienced by any The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). in a gravitational field.
Masses are attracted towards each other by gravitational force:
The Moon is attracted to the Earth, and the Earth is attracted to the Moon. Newton suggested that the Moon continually falls towards the Earth as it moves but the surface of the Earth continually drops away under the Moon. Hence, the Moon moves in a circular path around the Earth.