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  • Difficulty Level : Medium
  • Last Updated : 09 Aug, 2022

Force is defined as an external cause that a body experiences as a result of interacting with another body. Whenever two objects interact, a force is exerted on each object. The interaction or the encounter of the two objects ends when the two objects stop feeling any force on each other. Thus, we can say that forces exist when there is an interaction between two objects. Force is an outside factor that has the capability to change the resting or moving state of a certain body. It has size and motion. The force is applied in both a direction and at a point, referred to as the force’s direction and application, respectively. In this way, forces are divided into two Contact and Non-Contact forces, as discussed below.

 

What is Force?

A push or pull of an object is referred to as force in science. Force is created when two things contact. The amount and direction of force are both present. The magnitude of a force is used to represent its strength. A change in the direction or condition of motion of a body is caused by force. 

Any external element that has a tendency to change the state of motion or rest, when applied to an object is called force. Force is simply the push or pull upon an object resulting to the interaction between the two objects.

A force can cause an item to move from rest to motion or vice versa. Two or more things must interact with each other for a force to be created. For example, a force is applied by the wind when it propels a sailboat through the water, A force is also present when gravity pulls an apple downward. Things can move, change their speed, or change shape in response to forces. 

Unit of Force

  • Force is a vector quantity, this implies it has both mass and magnitude. The force acting on an object is represented by the symbol F or \vec F.
  • The SI unit of force is Newton (N). 1-Newton force is defined as the force required to accelerate a mass of 1 kg by 1 m/s2 in the direction of applied force.
  • In the CGS system, the unit of force is Dyne, and other units are poundal, pound-force, kip, kilo pond

Effects of Forces

When the force is applied to an object then it has different effects like it can change the shape of an object, or it can change the state of motion of that object. Let’s understand the effects of force:

  1. Change in shape: Force will cause a change in shape, for example when hammering a hot iron rod, the force exerted by the hammer will change the object’s shape, i.e. iron rod will be bent.
  2. Change in size: Force will cause a change in size, by stretching a rubber band, the force exerted by stretching a rubber band will cause an increase in the size of the rubber band.
  3. Change in direction: Force will cause a change in direction, for example hitting a football, the time you kick a ball, then its direction will get changed.
  4. Change in speed: When a batsman hit the moving ball with force will cause an increase in the speed of the ball. Also, the speed of force will depend on which direction it is applied, if we apply a force in the direction of a moving object then it will cause an increase in speed and when it applies against the moving object then it will decrease the speed of an object.
  5. Change in the state of motion-Rest and motion: Force will cause a change in motion, for example, the force exerted by the motor of the car will enable the car to move, while force exerted by the brake will enable the car to stop.

Formulas for Force

Force is defined by the vector product of mass m and acceleration a of the object. This can be written as,

F = ma

where, 

  • F is the applied force,
  • m is the mass of an object and 
  • a is the acceleration of the object.

Also according to Newton’s Second Law of Motion, force is given by the time rate of change of momentum. Mathematically, it is given as,

F=\dfrac{\text{d}\vec p}{\text{d}t}

where,

  • \text{d}\vec p   is the change in momentum, and 
  • dt is the change in time. 

But, momentum (\vec p)  is defined as the product of mass and velocity of the object as,

\vec p = m\vec v

where

  • m is the mass and
  • \vec v  is the velocity of the object.

Therefore, the force becomes:

\begin{aligned}F&=\dfrac{\text{d}(m\vec v)}{\text{d}t}\\&=m\dfrac{\text{d}\vec v}{\text{d}t}\\&=m\vec a\end{aligned}

Magnitude and Direction of Force

To move a large weight, the individual must pull or push it in the same direction. When two individuals push or pull weight in opposite directions, the resultant force is the sum of the two forces. The magnitude of a force expresses its strength. When forces are applied in the opposite direction, the size of the resultant force is reduced.

Furthermore, equal and opposing forces cancel out, thus the resulting force is zero. Force exerted to an item causes a change in velocity as well as a change in shape. Some forces operate on an item by making touch with it, whilst others act without making contact with the object. Touch forces are forces that act when an item comes into contact with them.

Contact forces include muscular forces and friction forces. Non-contact forces are those that may act without coming into touch with an item. Gravitational force, electromagnetic force, electrostatic force, and non-contact forces are all examples of forces.

Types of Force

A Force can act on an object with or without any contact. For example, if you are pushing or pulling a door then you must have contact with a door while if you have a bar magnet you can easily attract iron nails without having any contact with the nail. So in science, we have two types of forces, one is a contact force and the other is a non-contact force. Let’s see in detail what are they with their examples.

Contact Force

The forces which are applied to other objects only through physical touching are called contact forces. 

Examples of contact forces are muscular and frictional forces.

  1. Muscular Force- Muscular force is a contact force in which force is exerted by the muscles of the body. For example, jumping, kicking, running, walking, climbing, lifting, and pushing all are exerted by our muscles.
  2. Frictional Force- Frictional Force is a contact force that always opposes the body’s state of motion over another body. For example, if we stop paddling a bicycle, gradually it gets slows down and stops after covering some distance.

Non-Contact Force

The forces which are applied to other objects without any physical touching are called non-contact forces. 

Examples of non-contact forces are magnetic force, electrostatic force, and gravitational force. Now let’s discuss types of force in detail:

  1. Magnetic Force: Magnetic force is a non-contact force exerted by a magnet on any other magnetic substance. For example, if we bring a magnet near an iron nail then the magnet pulls them towards it since magnets exert force.
  2. Electrostatic Force: Electrostatic is a non-contact force that can be exerted by a charged object on another object from a distance. For example, when a plastic comb is rubbed in dry hair, then the electrically charged comb attracts a tiny piece of papers
  3. Gravitational Force: The Gravitational force is a non-contact force between two bodies having some mass. It is an attractive force. The force of attraction between the earth and any object is called the force of gravity.

Line of Action of a Force

Galileo used experiments to demonstrate that when there is no external force acting on an object, it moves at a constant speed. He could observe that a sphere’s speed rises as it rolls down an inclined plane because of its gravitational attraction on it.

The net force acting on an object is 0 when all the forces are equal and balanced. A net force acting on a body, however, can change either the magnitude or the direction of its velocity if all of the forces acting on it result in an unbalanced force, which indicates that the unbalanced force can accelerate the body. For instance, when a body is subjected to a number of forces and is determined to be at rest, we can infer that there is zero net force operating on the body.

The line of action of a force is the path it takes as it exerts its force on an object. The point of application of the force is the location where it is exerting its force on an object. The force of friction is the force that opposes the relative motion between the surfaces of two objects in contact and acts along the surfaces.

Solved Examples on Force

Example 1: Determine the force of an object with a mass equal to 500 kg and acceleration as 60 m/s2.

Solution:

Given that,

The mass of the object, m is 500 kg.

The acceleration, a is 60 m/s2

According to the force formula,

F = ma

Substituting the given values,

F = 500 kg × 60 m/s2

= 3 × 104 N

Example 2: How much net force is required to accelerate to a 20 kg box at 5 m/s2?

Solution:

Given that,

The mass of the box, m is 20 kg.

The acceleration of the box, a is 5 m/s2

According to the force formula,

F = ma

Substituting the given values,

F = 20 kg × 5 m/s2

= 100 N

FAQs on Force

Question 1: Which force is responsible for a charged balloon attracting another balloon?

Answer:

Electrostatic Force

Question 2: Which is the weakest force in nature?

Answer:

Gravitational Force is the weakest among all the four fundamental forces.

Question 3: Does a force always result in motion? 

Answer:

No, force never has to reverse the direction of a motion. For instance, moving a wall won’t change how it moves, etc.

Question 4: Is force a scalar quantity?

Answer:

Force is not a scalar quantity. Since it has both direction and magnitude. Therefore, force is a vector quantity.

Question 5: An apple falls from the tree, which force is responsible for these phenomena? Define it.

Answer:

Force of gravity is responsible for the fall of the apple. The Force of gravity is the force of attraction between the earth and any object.

Question 6: What is the net force? Explain with the help of an example.

Answer: 

The total of all the forces acting on a body is called the net force. For example, if we are pushing a heavy box in the same the direction the resultant force will be added and the box will move easily, while if two-person pushing the same box in an opposite direction then it gets difficult as the resultant forces acting on the force will be the difference between the two forces. 

Mathematically we can write,

Fnet = F1+ F2 (when force applying in the same direction).

Fnet = F1 – F2 ( when force acts in a opposite direction)


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