Concepts of Forces and Types of Forces

Concept of force

If an object is at rest, it will remain at rest unless some action is performed to make it move. Similarly, if an object is in motion, it will continue moving unless some action is taken to stop it.

Force is a push or pull acting on an object. It can make things start moving, stop moving, or change direction.

For example, a stationary cart or car must be pushed or pulled to make it move. These actions—pushing and pulling—involve what is known as force.

Pulling and pushing actions

Effects of forces

An object remains stationary when all the forces acting on it are balanced. When a new force is applied, the forces become unbalanced, resulting in various changes. These effects of unbalanced forces include:

1. Change in the state of motion of an object
2. Change in the way the object moves (its speed or acceleration)
3. Change in the shape or size of the object
4. Change in the direction in which the object is moving

For instance, to move a carton of books, a force must be applied by either pulling or pushing it. Similarly, pulling a rubber band stretches it, and pushing a spring compresses it. These are all examples showing that force is needed to cause motion or deformation.

Determination of the magnitude of force

To estimate the magnitude (size) of a force, a device called a spring balance is used. It consists of:

1. A coiled spring fixed at one end
2. A hook at the other end to attach the object
3. A pointer and a calibrated scale to read the force

When a force is applied by attaching a body to the hook, the spring stretches. The distance stretched is directly proportional to the magnitude of the force. The pointer indicates the force on the calibrated scale: the greater the force, the more the spring stretches.

A spring balance

Measuring forces using a spring balance

A spring balance can measure both vertical and horizontal forces, as shown in Figures (a) and (b).

For example, in Figure (a), the weight of an empty box is shown on the spring balance. If the box is filled with sand, the pointer shows a higher value, because the weight of the sand is added.

To find the weight of the sand alone, subtract the weight of the empty box from the weight of the filled box:

$$\text{Weight of sand} = \text{Weight of filled box} - \text{Weight of empty box}$$

Spring balance