Force and System of Forces

Force is that which changes or tends to change the state of rest of uniform motion of a body along a straight line. It may also deform a body by changing its dimensions. The force may be broadly defined as an agent which produces or tends to produce, destroys or tends to destroy motion. It has a magnitude and direction.

Mathematically,

                                                            Force = Mass× Acceleration

                                                                   F = m a

Where, F - Force

            m - Mass

             a - Acceleration

Characteristics of Force

1) Magnitude: Magnitude of force indicates the amount of force (expressed as N or kN) that will be exerted on another body

2) Direction: The direction in which it acts

3) Nature: The nature of force may be tensile or compressive

4) Point of Application: The point at which the force acts on the body is called point of application

Units of Force

1) In C.GS. System

In this system, there are two units of force: (i) Dyne and (ii) Gram force (gmf). Dyne is the absolute unit of force in the C.G.S. system. One dyne is that force which acting on a mass of one gram produces in it an acceleration of one centimeter per second².

2) In M.K.S. System

In this system, unit of force is kilogram force (kgf). One kilogram force is that force which acting on a mass of one kilogram produces in it an acceleration of 9.81 m/ sec².

3) In S.I. Unit

In this system, unit of force is Newton (N). One Newton is that force which acting on a mass of one kilogram produces in it an acceleration of one m /sec².

                                                                1 Newton = 10⁵ Dyne

Effect of Force

A force may produce the following effects in a body, on which it acts.

1. It may change the motion of a body. i.e. if a body is at rest, the force may start its motion and if the body is already in motion, the force may accelerate or decelerate it.
2. It may retard the forces, already acting on a body, thus bringing it to rest or in equilibrium.
3. It may give rise to the internal stresses in the body, on which it acts.
4. A force can change the direction of a moving object.
5. A force can change the shape and size of an object

Principle of Physical Independence of Forces

It states, “If a number of forces are simultaneously acting on a particle, then the resultant of these forces will have the same effect as produced by all the forces.”

System of Forces

When two or more forces act on a body, they are called to form a system of forces. Force system is basically classified into the following types.

1) Coplanar Forces

The forces, whose lines of action lie on the same plane, are known as coplanar forces.

Fig. 1 Coplanar Forces

2) Collinear Forces

The forces, whose lines of action lie on the same line, are known as collinear forces.

Fig. 2 Collinear Forces

3) Concurrent Forces

The forces, which meet at one point, are known as concurrent forces. The concurrent forces may or may not be collinear.

Fig. 3 Concurrent Forces

4) Coplanar Concurrent Forces

The forces, which meet at one point and their line of action also lay on the same plane, are known as coplanar concurrent forces.

Fig. 4 Coplanar Concurrent Forces

5) Coplanar Non-Concurrent Forces

The forces, which do not meet at one point, but their lines of action lie on the same plane, are known as coplanar non-concurrent forces.

Fig. 5 Coplanar Non-Concurrent  Forces

6) Non-Coplanar Concurrent Forces

The forces, which meet at one point, but their lines of action do not lie on the same plane, are known as non-coplanar concurrent forces.

Fig. 6 Non-Coplanar Concurrent  Forces

7) Non-Coplanar Non-Concurrent Forces

The forces, which do not meet at one point and their lines of action do not lie on the same plane, are called non-coplanar non-concurrent forces.

Fig. 7 Non-Coplanar Non-Concurrent  Forces

8) Parallel Forces

The forces, whose lines of action are parallel to each other, are known as parallel forces.

Fig. 8 Parallel Forces