A force is an influence, such as a push or pull, that makes an object accelerate. In physics, an object is said to accelerate when it changes either its speed or direction. Forces can either be contact forces, such as an object pushing another object, or non-contact forces, such as gravity or magnetism, which act invisibly over a distance.
The magnitude, or strength and direction, of a force is measured in a unit called the Newton, named after Sir Isaac Newton, the famous scientist who helped discover the laws of physics.
When two equal forces going the exact opposite direction meet, they cancel each other out perfectly. For example, if you and a friend each try to push a box with the same force, the box will not change its speed or direction. If, however, both forces act in the same direction, the forces get added together. So if you and a friend both push the same box from the same side this time, the box will accelerate twice as if you push it alone.
Physicists have discovered 4 basic, or fundamental, forces at work in the universe. Other forces, like friction, buoyancy, or even pushing a box, can all be explained in terms of these 4 forces:
While mass is a measurement of the amount of matter in an object, weight is actually a force. When you step on the scale to measure your weight, what you're actually measuring is the force of gravity from Earth pulling you down to its surface.
