Understanding Force in Physics: Causes, Effects & Examples

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Force

Force, in physics, the pushing or pulling agency that makes (or tends to make) objects speed up, slow down, or change direction. Like time and speed, force in itself cannot be seen. Instead, it is a cause whose effect can be measured, as in the workings of gravitation, of electricity and magnetism, and of nuclear reactions. Some forces have specific names. For example, a force that resists the movement of one object against another is called friction; a force that turns or tends to turn an object is called torque; and the force with which the earth's gravity pulls on an object is called weight.

The calculation and measurement of forces is of fundamental importance in physics, engineering, and other sciences. The scientific understanding of force began with the work of Sir Isaac Newton (1642-1727). He used the idea of force in his three laws of mechanics.

A force acting on an object is expressed in terms of the object's mass (the amount of matter it contains) and the acceleration (change of motion) that the force tends to give the object. (For an explanation of acceleration, The relationship between force (F), mass (m), and acceleration (a) is given by the formula F=ma.

Units of Force

Force can be expressed in two kinds of unitsgravitational and absolute. The gravitational units are based on acceleration due to gravity; the absolute units, on acceleration given in terms of a standard unit of length.

The most familiar gravitational units of force are the pound-force and the kilogramforce. Each of these units is usually called by the same name as the unit of mass used in defining it: the pound and the kilogram, respectively.

A Pound-force

is the force that gives a mass of 1 pound the same acceleration as that produced by gravity (about 32 feet per second per second).

A Kilogram-force

is the force that gives a mass of 1 kilogram the same acceleration as that produced by gravity (about 9.8 meters per second per second).

The most common absolute units of force are the poundal, newton, and dyne.

A Poundal

is the force that gives a mass of 1 pound an acceleration of 1 foot per second per second.

A Newton

is the force that gives a mass of 1 kilogram an acceleration of 1 meter per second per second. It is the basic unit of force in the SI, the internationally accepted form of the metric system.

A Dyne

is the force that gives a mass of 1 gram an acceleration of 1 centimeter per second per second.