## What is force?

**Clearly, it is an external agency that makes you do certain things under a strain**.

The same concept applies to forces in physics. We define force in physics as the external agencies that alter a state of motion. Sir Isaac Newton, established a formula connecting the force and the motion of an object in a straight line and it is widely called as Newton’s second law of motion. It states, that when an acceleration of magnitude a is effected on an object of mass m, the product m*a is defined as the force F, that causes the acceleration on that mass. Algebraically it is stated as,

**F=ma**

Thus, a force is defined in physics
this way. Force is a vector quantity which has both magnitude and
direction. Hence to change the direction of motion of an object even
with the same magnitude of velocity a force has to be applied.

## Unit of Force

**1) Absolute system**

2) Gravitational system

2) Gravitational system

The measurement of forces in absolute system are not dependent on gravitational force, whereas, measurement of forces in gravitational system are dependent on gravitational forces. Hence, the measure of forces in gravitational system differ on other planets compared to earth.

When a mass of 1 pound is subjected to an acceleration of 1 ft/sec

^{2}, the force applied is called 1poundal. The unit is abbreviated as pdl.

A pound force is defined as the gravitational force exerted on 1 pound mass. It is denoted as lbf. When we say that the weight of the person is 150 pounds, we actually mean 150 lbf.

Poundal and pound force are the units of measurement of forces in fps system.

In metric system a force of 1 kilogram force is the force exerted on 1 kilogram mass. It is similar to pound force in fps system. It is denoted as kgf.

In cgs system a force is measured in terms of dynes. A force of 1 dyne produces an acceleration of 1cm/sec

^{2}on a mass of 1 gram.

In SI units, the unit of force is defined as newton. This unit is named in the honor of Sir Isaac Newton who actually had given the definition of a force. One newton produces an acceleration of 1 m/sec

^{2}on a mass of 1 kilogram. It can easily be derived that 1 newton is equal to 10

^{5}dynes. The unit of newton is abbreviated as N.

The gravitational units and absolute units are related by acceleration due to gravity. That is,

1 pound force