# Translations of Encyclopedia about Physics

## Force

Physics examines the effect each force has on some object, where the force may either deform the object or cause it to change its path of movement. For example ,if we push down on a spring, the deformation force held within the spring in its compressed state will hold a certain amount of tension.

Forces act on each object, even in their static or calm states.

A force may be either tensile, pushing, or rotating, in which case we are speaking about momentum.

The force which acts on every object is gravitational force. Gravitational force works between all objects, but only when at least one of the objects has a greater amount of mass, such as the earth, does the force become significant and starts overcoming the forces of other, surrounding objects. Two magnets also exert a gravitational force on each other, although imperceptible to us.

The gravitational force of the sun causes the earth to revolve around it, for the same reason that the moon revolves around the earth. With satellites, the force of gravity is used to maintain the satellite in a fixed position of orbit around the earth.

If the force of two objects is applied to one other, it is said that those object lie in the same force system.

It is very rare that only a single force would act on an object. The joint affect of several forces results in a combined, resulting force whose magnitude and direction are the result of the directional vectors and sizes of the individual forces.

An object is considered in a balanced state when the forces applied to it are balanced (cancel each other out). If a certain object presses on a table due to the gravitation force relating to its weight, then the table exerts an equal reactive force against that object. The resulting force is zero, meaning that the objects remains in the same position.

According to the law of maintaining energy, various forces acting together and which exert a certain amount of energy on an object create new forces which result in the transfer of energy. If we intend to move a certain object, we must first overcome the force of traction (static friction). If there is surface friction, the resulting movement of the object is slowed down. Air resistance also limits an object’s speed.

Frictional force is directly proportional to the coarseness of the contacted surface against the friction of the contacted object. This is why we use lubricants, such as motor oils, which reduce the coarseness of surfaces, to prevent unwanted deterioration of moving parts.

Newton’s laws of movement:

1. An object remains idle or continues to move in a straight line when no force acts it.
2. If some force acts on an object, its state of movement changes.

The change of speed depends on the object’s weight and the size of the force acting on it.

3. If the force of one object acts on another object, then that second object exerts the same amount of force on the first object, although in an opposite direction (reaction).

The unit of a force is the newton. A newton is a force which causes an object of mass 1 kg to accelerate at 1 m/s2, which is about one tenth the acceleration created by the earth’s gravitation.

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