[Physics Class Notes] on Force and Motion Pdf for Exam

There are different types of motion related to the human body. Do you know what causes and obstructs motion in the body or object? The answer is the application of force. In general physics, the term force and motion are interrelated and are two sides of the same coin. For example, the interdependence of force and motion can be viewed from the perspective of throwing a ball and catching it back. A force causes interaction between two or more bodies and when that remains unobstructed generates a change in the state of motion. To figure out this relationship existing between force and motion we have to understand the terms individually. 

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What is Force? 

To comprehend what is force, we have to think in terms of pull and push. The push and pull acting on an object or energy as a movement or attribute of physical activity is defined as forced. 

Similiar to push and pull, words like squeeze and stretch also explains the concept of what forces can do. This mainly happens when two entities come in contact. Based on Newton’s universal law of gravitation every object in this universe exerts a force on other objects.  

What is the S.I. unit of Force?

If you want to know what is the S.I. unit of force, we have to know about Sir Issac Newton who first studied gravity and force. So, it is obvious what is the unit of force. It is called the Newton.

F = ma

1 Newton = 1 kg x 1 m/s2

What is Force Measured in? 

These are the units of force that explain how force is measured. 

• This is a standard international system of a unit (SI unit) which is expressed in Newton (N).

• There is a centimetre gram second system of a unit (CGS unit) which is expressed in dyne.

• There are other units like pound-force, kip, poundal, kilopound. 

What are the Different types of Force?

There are two fundamental types of forces that exist:

1.  Contact forces

2.  Non-contact or action-at-distance forces

Now let us understand these types of forces and their subtypes in some detail.

A force that is exerted on an object or body directly through being in contact with it or being in contact with its medium is known as contact forces. The various types of contact forces are:

1. Muscular forces- Have you ever seen a bodybuilder lift weights or a person pushing his broken car? Both of them do so by applying what is known as muscular forces. As the name suggests, this is the type of contact force in which the muscles are used to exert force on another object to bring it in motion, lift it, change its shape or size, make it stop, or make it move faster or slower.

2. Frictional forces- Every object in motion has a frictional force acting on it. It can be described as a force that causes resistance between the surface of the object in motion and the surface it is moving on. When you light a matchstick or apply brakes to a moving vehicle frictional force is present between the surfaces of both objects, which induces fire in the matchstick and stops the vehicle from moving.

3. Normal force- An object lying on a flat surface can seem to be still but in reality, some forces are acting on it. The force of gravity and the atmosphere act on the object to make it absolutely still. It is called a normal force.  

4. Applied force- Applied force is simply the force that is applied by someone on an object to make it move in different directions.

5. Tension force– It is the type of force that is transferred through a cable, wire, rope, or any similarly long object that is anchored to another object. It creates tension between both the objects exerting the same pressure on both of them.

6. Spring force- As the name suggests, this is the type of force that is induced through a spring- compressed or stretched – onto another object to either push or pull it.

7. Air resisting force- Frictional force that is exerted by the air on an object is called air resisting force. Aeroplanes, birds, kites, and other types of flying objects in the air experience this.

The force that is exerted on an object without the object being in contact with anything is known as non-contact forces. The different types of non-contact forces are-

1. Gravitational force- The Earth has a gravitational force that attracts all the objects and substances of Earth towards it. There is no contact between the object and the gravity, yet this force is exerted.

2. Magnetic force- Magnets exert different amounts of force on different objects and this force is called the magnetic force.

3. Electrostatic force- Similar to magnets, electrically charged bodies also induce a certain amount of force on different objects which are called electrostatic forces.

What is Motion?

We can define what is motion in simple words regarding the change of position of the body to time. A train moving, water flowing from the tap, boy walking, etc., all exhibits the state of motion. The act of breathing is also defined as motion. Therefore, every physical process that we experience in this universe is composed of some or other sort of motion. Neither a motion can be swift, nor it can be slow. All this explains what is the meaning of motion. It is vital to understand the concept of motion because it has relevance in the physical world. 

What is the meaning of Motion?

Various terms help us to describe further what is motion in the actual sense. It includes distance, displacement, time, and speed. With terms like displacement and distance, we can describe a change in position. Distance is not easy to explain since it depends upon the path that one has taken. On the contrary, displacement is an easier concept because it always gives a definite answer. It is the shortest distance covered between the two points. If the motion is in the straight line, distance and displacement will be the same. If the motion is not in a straight line, the distance always tends to be greater than the displacement. 

The Relation between Force and Motion

Force and motion are deeply interconnected with each other. What force can do is produce motion in an object or body. For instance, an object is moving and we can say that a force is acting or must
have been acted upon to cause the state of motion. When force is applied, it changes the position of the object concerning time resulting in motion. The motion, in other words, is described as a change in speed or change in direction. Isaac Newton was the first to discover the relation between force and motion. He came to three conclusions: 

• Force can accelerate the object. 

• Force can decelerate the object. 

• Force can cause a change in the direction of the object. 

Did you Know?

Force has a different effect on the object or body. These are listed below:

• Force application can make a body at rest move.

• Force can accelerate or decelerate the speed of a moving body.

• Force can completely stop a moving body.

• Force can also change the direction of a moving body

• Force can transform the shape and size of a body.  

Force and motion are the prime concepts of physics that students have to learn and understand at the basic level. This foundation of knowledge will aid them to grab hold of the advanced conceptual topics in higher classes.