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What Are Forces?

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.

Did you know?

  • Forces can add together or cancel each other out.

    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.

  • There are 4 basic forces in the universe that make up all other forces.

    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:

    • Gravity, which is what makes things fall to the ground and keeps the planets in orbit around the sun.
    • Electromagnetism, the forces between particles that have electrical charge. This force is what makes magnets work and powers electronics like computers and TVs.
    • The strong nuclear force, which is what holds the protons and neutrons in the nucleus of an atom together.
    • The weak nuclear force, which is responsible for certain kinds of radioactive decay and is important for how the sun produces energy.

  • Weight is actually a force—mass is not.

    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.