There are two main categories of forces:
Contact forces require physical contact between objects. Examples include:
* Normal force: The force exerted by a surface perpendicular to an object in contact with it.
* Friction: The force that opposes motion between two surfaces in contact.
* Tension: The force transmitted through a stretched cable, rope, string, or similar object.
* Air resistance: The force that opposes the motion of an object through air.
Non-contact forces can act between objects that are not touching. Examples include:
* Gravity: The force of attraction between any two objects with mass.
* Electromagnetism: The force that arises from the interaction of electric charges and magnetic fields. This includes forces like the attraction between magnets and the force that holds electrons in atoms.
So, while contact forces require physical contact, non-contact forces can act over distances. For instance, the Earth's gravity pulls on the moon even though they are millions of kilometers apart.
