FORCES AND FIELDS
What is force?
A force is a type of energy that acts on an object. It can act on an object:
* to push it
* to pull it
* to stop it; or
* to change its shape
There are a number of different forces around us, for example, gravity, which keeps us on the ground, and magnetic force, which holds notices to your fridge. You exert (apply) force when you tap keys on the keyboard or push the mouse around. Even if you stay still, your body still uses force, such as when your heart pumps blood around your body or the muscles in your eye contract to focus on these words.
Types of forces
A contact force occurs when two or more objects are touching each other and the force contained within one object influences the force in the other/s because they are in contact. Observe contact force when you next throw a ball - the energy from your arm and hand pushes the ball into the air.
Contact force also includes invisible forces such as friction, air resistance and buoyancy. These forces are in contact with the object that they affect, even if you cannot see them.
It is important to distinguish the difference between a contact force that you cannot see and a non-contact force. A non-contact force is one that acts on an object without touching it. Instead, a force will interact with the object within a force field, which is an area of influence surrounding the force.
A magnet is an example of a non-contact force. If you hold a magnet close to a paperclip, the magnetic force will attract the paperclip. If you held the magnet in one hand and the paperclip in another and spread your arms far apart, the paperclip would be beyond the force field of the magnet and the magnet would not attract it.
Other non-contact forces include gravity and electricity. The size of the force field is related to the size of the force. Large magnets, for example, have a bigger area of influence than small magnets.
More than one force
If you throw a...