Define what is Motion and Force?
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.
Contact forces
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:
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.
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.
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.
Applied force- Applied force is simply the force that is applied by someone on an object to make it move in different directions.
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.
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.
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.
Non-contact forces
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-
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.
Magnetic force- Magnets exert different amounts of force on different objects and this force is called the magnetic force.
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.
FAQs on Force and Motion
1. What are force and motion in physics?
In physics, a force is defined as a push or a pull on an object that results from its interaction with another object. It is a vector quantity, meaning it has both magnitude and direction. Motion is the change in the position of an object with respect to its surroundings over a period of time. Essentially, force is the cause, and a change in motion is often the effect. For a detailed exploration, you can refer to Vedantu's page on Force and Motion.
2. What are the main effects a force can have on an object?
A force can produce several effects on an object. It can:
- Cause a stationary object to move.
- Stop a moving object.
- Change the speed of a moving object (accelerate or decelerate it).
- Change the direction of a moving object.
- Change the shape or size of an object.
These effects of forces are fundamental to understanding interactions in the physical world.
3. How is force related to acceleration according to Newton's Second Law?
Newton's Second Law of Motion establishes a direct relationship between force, mass, and acceleration. It states that the acceleration of an object is directly proportional to the net force applied to it and inversely proportional to its mass. This is mathematically expressed by the formula F = ma, where 'F' is the net force, 'm' is the mass, and 'a' is the acceleration. In simple terms, a larger force will produce greater acceleration for a given mass.
4. What is the difference between balanced and unbalanced forces?
The key difference lies in their effect on an object's state of motion:
- Balanced Forces: These are two or more forces of equal magnitude acting on an object in opposite directions. The net force is zero, so there is no change in the object's motion. An object at rest stays at rest, and a moving object continues at a constant velocity.
- Unbalanced Forces: These occur when the forces acting on an object are unequal in magnitude. The net force is non-zero, which causes a change in the object's motion, meaning it will accelerate.
For instance, a book resting on a table is subject to balanced forces (gravity and the normal force), so it doesn't move.
5. What are the common types of motion?
Motion can be broadly categorised based on the path of the object:
- Linear Motion: The object moves in a straight line (e.g., a car on a straight road).
- Rotary Motion: The object rotates around a fixed axis (e.g., the blades of a fan).
- Oscillatory Motion: The object moves back and forth about a mean position (e.g., the swinging of a pendulum).
Real-world movements are often a combination of these basic types of motion.
6. What is inertia, and how does it relate to Newton's First Law of Motion?
Inertia is the natural tendency of an object to resist any change in its state of rest or uniform motion. Newton's First Law, often called the Law of Inertia, formalises this concept. It states that an object will remain at rest or continue to move at a constant velocity unless acted upon by an external unbalanced force. An object's mass is a measure of its inertia; the more massive an object, the harder it is to change its state of motion.
7. Can an object be in motion even if the net force acting on it is zero?
Yes, an object can be in motion with a zero net force. According to Newton's First Law, a force is required to *change* motion (i.e., to accelerate), not to *maintain* it. If the net force is zero, an object will continue to move at a constant velocity (constant speed in a straight line). For example, a satellite in deep space, far from any significant gravitational pull, will travel in a straight line at a constant speed without any propulsion.
8. How does Newton's Third Law explain the propulsion of a rocket?
Newton's Third Law states that for every action, there is an equal and opposite reaction. This principle is perfectly demonstrated by a rocket launch. The rocket propels itself by pushing hot exhaust gases downwards at high velocity (the action force). In response, the gases exert an equal and opposite force upwards on the rocket (the reaction force). This upward reaction force overcomes gravity and accelerates the rocket into the sky.
9. What is the difference between contact and non-contact forces?
The primary difference is whether the interacting objects need to be in physical contact:
- Contact Forces: These forces act on an object by direct contact with it. Examples include frictional force, tension in a rope, air resistance, and the normal force from a surface.
- Non-Contact Forces: These forces act on an object without coming physically in contact with it. They act over a distance through a field. Examples include gravitational force, electrostatic force, and magnetic force.
You can learn more about contact and non-contact forces on Vedantu.
10. Why is momentum a key concept for understanding force?
Momentum (mass in motion, calculated as p = mv) is crucial because Newton's Second Law, in its most complete form, states that force is the rate of change of momentum. This definition (F = Δp/Δt) is more fundamental than F=ma because it also applies to systems where mass is not constant, such as a rocket burning fuel and becoming lighter. Understanding the relationship between force and momentum provides a deeper insight into dynamics.
11. What is meant by a 'resultant force'?
A resultant force, or net force, is the single force that represents the combined effect of all the individual forces acting on an object. It is calculated by finding the vector sum of all forces. If the resultant force is zero, the forces are balanced, and the object's acceleration is zero. If the resultant force is non-zero, the object will accelerate in the direction of this force, as described by Newton's Second Law.
12. Who is credited with discovering the fundamental laws of motion?
Sir Isaac Newton is credited with formulating the three fundamental laws of motion, which form the bedrock of classical mechanics. He published these laws in his seminal work, "Philosophiæ Naturalis Principia Mathematica," in 1687. These laws provide a comprehensive framework for understanding how objects behave when at rest, in motion, and when acted upon by forces.
