Effects of Force With Examples
The study of Physics Topics involves the exploration of matter, energy, and the forces that govern the universe.
When we want to open a door, we have to push the door handle. And when we want to close the door, we have to pull the door handle with our hand. This means that to move a body (or an object), it has either to be pushed or pulled. A push or pull on a body is called force. The direction in which a body is pushed or pulled is called the direction of force. We open or close a door by applying force. Now, when we push the door to open it/ we apply a force on the door in a direction away from us. And when we pull the door to close it, then we exert a force on the door in a direction towards us.
Forces are used in our everyday actions like pushing, pulling, lifting, stretching, twisting and pressing.
For example, a force is used when we push (kick) a football; a force is used when we pull the drawer of a table ; a force is used when we lift a box from the floor ; a force is used when we stretch a rubber band ; a force is used when we twist a wet cloth to squeeze out water; and a force is used when we press the brake pedal of a car. The fallen leaves of trees fly away with wind because the force of wind pushes them away. Even the roofs of some huts fly away during a storm because the force of strong winds pushes them away. And when we fly a kite, we can actually feel the force (or push) of the wind on it. We will now describe the effects of force.
A force cannot be seen. A force can be judged only by the effects which it can produce in various bodies (or objects) around us. A force can produce the following effects :
- A force can move a stationary body.
- A force can stop a moving body.
- A force can change the speed of a moving body.
- A force can change the direction of a moving body.
- A force can change the shape (and size) of a body.
We will now give examples of all these effects produced by a force when it acts on a body (or an object).
If we kick a football kept on the ground with our foot, then the football starts moving (see Figure). In this case, the force of our foot moves a stationary football. Similarly, the force of engine can move a stationary car. From these examples we conclude that a force can make a stationary body move. It is a common observation that a football moving on the ground stops after some time. In this case, the force of friction of ground stops the moving football.
Similarly, the force of brakes can stop a moving car. From these examples we conclude that a force can make a moving body stop.
Suppose we are moving on a bicycle at a certain speed. Now, if someone pushes the moving bicycle from behind, then the speed of bicycle increases and it will move faster. On the other hand, if someone pulls the moving bicycle from behind, then the speed of bicycle decreases and it will move slower. Thus, a push or pull can change the speed of a moving bicycle. But a push or pull is called force. So, we can say that a force can change the speed of a moving bicycle (or any other moving body). If the force is applied in the direction of motion of a body, its speed increases.
On the other hand, if the force is applied in the direction opposite to the direction of motion of a body, then its speed decreases. Let us take another example. When a ball is dropped from a height, its speed goes on increasing. The speed of a falling ball (or any other falling body) increases because the earth applies a pulling force on it which is called the force of gravity.
It is the force of gravity of the earth which pulls a falling ball towards its centre and increases its speed. On the other hand, when a ball is thrown upwards, then its speed goes on decreasing. This is because the earth applies a pulling force of gravity on the ball in the downward direction (opposite to the motion of the ball).
In a tennis match, when a moving tennis ball is hit by a racket, then the direction of tennis ball changes and it goes in a different direction (see Figure). In this case, the force exerted by the tennis player’s racket changes the direction of a moving tennis ball. Similarly, in a cricket match, when a moving cricket ball is hit by a bat, then the direction of cricket ball changes and it goes in another direction. In this case, the force exerted by the cricket player’s bat changes the direction of a moving cricket ball.
In the game of carrom, when we take a rebound, then the direction of striker changes. This is because the edge of the carrom board exerts a force on the striker. If we blow air from our mouth on the smoke rising up from a burning incense stick (agarbatti), then the direction of motion of smoke changes. In this case, the force exerted by the blowing air changes the direction of moving smoke. From these examples we conclude that a force can change the direction of motion of a moving body.
If we take a light spring and pull it at both the ends with our hands, then the shape and size of the spring changes (see Figure). The turns of the spring become farther apart and its length increases. In this case, the force of our hands changes the shape and size of the spring. Here are some more examples in which a force changes the shape (and size) of an object. The shape of dough (kneaded flour) changes on pressing with a rolling pin (belan) to make chapatis.
When we press the dough with a rolling pin, we apply force. So, we can say that the shape of dough changes on applying force. The shape of kneaded wet clay {geeli mitti} changes when a potter converts it into pots of different shapes and sizes. This happens because the potter applies force on the kneaded wet clay.
The shape of a tooth paste tube (or an ointment tube) changes when we squeeze it because we apply force while squeezing it. Similarly, the shape of a sponge, tomato, balloon, rubber ball or tennis ball changes on pressing. And the shape and size of a rubber band changes on stretching. From all these examples we conclude that a force can change the shape and size of a body (or object).
We can now define force as follows : A force is an influence which tends to set a stationary body in motion or stop a moving body; or which tends to change the speed and direction of a moving body; or which tends to change the shape (and size) of a body.