Force may be defined as push or pull. In physics, a force is any influence that causes or tends to cause an object to undergo a change in state of motion, a change in direction, or a change in shape. Force can change the velocity, bring the object at rest in motion or stop the object in motion. A force is a vector quantity as it has both magnitude and direction. Force is measured in “Newtons” (N) named after English physicist and mathematician Sir Isaac Newton.
Formula to measure Force is given as:
F = m × a
where, is mass (in kg) of the object on which the force is acting and a is the acceleration (in m/s2) produced in the object. A force that produces and acceleration of 1 m/s2 in an object of 1 kg is equivalent to 1 Newton.
We use force very often in our daily life. We push or pull the door to close it or open it. To move or lift an object we apply force. If we squeeze a rubber ball its shape and size changes. It comes back to its usual state as soon as we remove the force. In the game of soccer the players hit the ball to change its direction and speed.
Forces acting between bodies can be divided in to two broad categories.
- Contact forces are those forces which act when the two interacting are physically in contact with each other. Below are types of contact forces.
- Frictional force is the force exerted by a surface as an object moves across it or tries to move across it.
- Air resistance acts upon objects as they travel through the air. It often opposes the motion of an object.
- Tension forces that are transmitted through rope, string, wire or cable when it is pulled tight by forces acting from opposite end. It acts along the length of the wire and pulls equally on the opposite ends of the wire.
- Applied forces are the forces that are applied to an object by another object.
- Spring force is also a kind of contact force that is exerted by a compressed or stretched spring upon any object that is attached to it.
- Normal forces are exerted upon an object that is in contact with another stable object fall in this category.
2. Action-at-a-distance forces are those forces that result even when the two interacting objects are not physically in contact with each other, yet are able to exert a push or pull despite their physical separation.
- Gravitational forces between sun and planets act despite the large spatial distance between them.
- Magnets push or pull each other even if they are not in physical contact with each other as magnetic forces are in action despite the distance between the magnets.
- Electric forces are action-at-a-distance forces. For example, the protons in the nucleus of an atom and the electrons outside the nucleus experience an electrical pull towards each other despite small separation between them.
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