Force And Motion

Various motions of body which we see around us are based on the relationship between force and motion. For example: Throwing a ball, hammering a nail etc. This article will explain you the relationship force and motion. Let us first understand the meaning of force and motion individually. Later on the relationship between them.

Force:

We can say that force is a push or pull acting on an object. This push or pull acts when this object is in contact with some other object.  For example if there are two bodies of mass M and m, and they are kept in such a way that the body with mass m is resting over the body with mass M. In physics we say that these two bodies will exert forces on each other. So we can say that whenever there is an interaction of two or more bodies, force is a part of the interaction.

Motion:

In simple words, whenever a body is moving, we say it is in motion. For instance if a boy is walking down the street from his school to his home, we will say that the boy is in motion. But imagine if the boy stops for 5 minutes in the way and sits down. If someone asks at that time if the boy is in motion, the answer will be ‘No’. From this we can infer that motion of a body is dependent on time. In physics we say that motion is the change in the position of a body with respect to time.

Force and Motion relation:

Force and motion are deeply related in nature.  We can say that force is the cause of motion. Suppose something is moving, we can say that some force must be acting on it or some force must have acted on it which produced this motion. If a person is walking, and hence in motion, there must be some force acting on it which is making him move. What is this force? This force is the muscular force of his body.

Before we delve into the relationship between force and motion, let us first take a quick look into what is meant by force. Simply put, force is either a push or a pull. Force is defined as “any interaction that, when unopposed, will change the motion of an object”.  By the definition itself, it is clear that force affects the state of motion of an object.

But what exactly is does ‘state of motion’ mean? In physics, motion is defined as the change in position with respect to time. In simpler words, motion refers to the movement of a body. Typically ,motion can either be described as

  • Change in speed, or
  • Change in direction.

Sir Isaac Newton was the first person to discover the relation between motion and force. From his studies in force and laws of motion, we can come to the following three conclusions:

1.   Force can cause a body to accelerate

When force is applied to a body in rest, it starts to move, provided that there is no greater force opposing it. When you throw the ball towards the batsman while playing cricket, the ball starts to move forward from its initial position of rest in your hands.

When something begins to move from a state of rest, it accelerates. Acceleration can be described as the positive change in velocity over a period of time.

Similarly, if force is applied in the same direction of movement of a moving object, it accelerates. For example, if you rotate the pedal of a bicycle, it will go faster.

Force And Motion

2. Force can cause a body to decelerate 

On the other side of the spectrum, if force is applied on the opposite direction of a moving object, it will decelerate or slow down and eventually stop altogether if the force is continued to be applied.

For example, when a goalkeeper stops a ball, he causes it to decelerate and stop.

Force And Motion  3. Force can cause a body to change directions

When force is applied on an object in an angle different to its direction of motion, it causes the object to change motion. Almost every ball game uses this principle. The speed can be maintained if the force is applied in a perpendicular angle but the velocity will changeForce And MotionTo wrap up, force and motion are two heavily connected entities. Force can result in the acceleration, deceleration, change in direction or total cessation of motion.


Practise This Question

A force can: