What is a force?
A force is anything that can cause a change to objects. Forces can:

• change the shape of an object
• move or stop an object
• change the direction of a moving object.

A force can be classified as either a contact force or a non-contact force.
A contact force must touch or be in contact with an object to cause a change. Examples of contact forces are:

• the force that is used to push or pull things, like on a door to open or close it
• the force that a sculptor uses to turn clay into a pot
• the force of the wind to turn a windmill

A non-contact force does not have to touch an object to cause a change. Examples of noncontact forces are:

• the force due to gravity, like the Earth pulling the Moon towards itself
• the force due to electricity, like a proton and an electron attracting each other
• the force due to magnetism, like a magnet pulling a paper clip towards itself

The unit of force is the newton (symbol N ). This unit is named after Sir Isaac Newton who first defined force. Force is a vector quantity and has a magnitude and a direction. We use the abbreviation F for force.
There is a popular story that while Sir Isaac Newton was sitting under an apple tree, an apple fell on his head, and he suddenly thought of the Universal Law of Gravitation. Coincidently, the weight of a small apple is approximately 1 N.

There is a popular story that while Sir Isaac Newton was sitting under an apple tree, an apple fell on his head, and he suddenly thought of the Universal Law of Gravitation. Coincidently, the weight of a small apple is approximately 1 N.

Force was first described by Archimedes of Syracuse (circa 287 BC - 212 BC). Archimedes was a Greek mathematician, astronomer, philosopher, physicist and engineer. He was killed by a Roman soldier during the sack of the city, despite orders from the Roman general, Marcellus, that he was not to be harmed.

his chapter will often refer to the resultant force acting on an object. The resultant force is simply the vector sum of all the forces acting on the object. It is very important to remember that all the forces must be acting on the same object. The resultant force is the force that has the same effect as all the other forces added together.

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Physics 11.II Force, Momentum, Impulse

High School Students Studying the Sciences Physics​