Force- Unit and Dimension, Types, Formula, Application, Effects

Have you watched the Star Wars movie? If so, then you must have come across a very famous dialogue “May the force be with you” from that movie. Actually we use the term force in our daily conversation very frequently. If I ask you to push or pull the water bottle kept on a table you will easily do it. But if I ask you to pull or push the table itself then you will have to apply a lot of force. In this article we will learn about common forces that are encountered in mechanics.

Table of Contents

Force
Unit and Dimension of Force
Effect of Force
Types of Forces
Practice Problems of Force
FAQs of Force

Force

Definition: A push or pull that changes or tends to change the state of motion. The state of motion is defined by the velocity of the body.
Note: Force has both magnitude and direction. Also it follows the laws of vector algebra. So Force is a vector quantity.
In the following picture, the girl is applying force by pushing the cart and the boy is pulling the cart.

Unit and Dimension of Force

SI unit of force is Newton (N) & CGS unit is dyne.
Dimension of force is MLT^-2.
1 N=10⁵ dyne.

Effect of Force

It changes the direction of motion of the body.
It changes the speed of the body.
It changes the shape of the body.

Types of Forces

Non-contact Forces

This force is applied to an object by another body that is not in direct contact with it. These forces come into play when objects do not have any physical contact with each other.

Note: Non-contact forces are also called Field forces.

Examples of Non-contact forces:

Gravitational force
Electrostatic force
Magnetic force
Strong nuclear force
Weak nuclear force

Weight

Force experienced by a body due to gravity near the earth's surface is called weight.

Gravitational force can be exerted between any two bodies having masses, whether they may be the size of planets or microscopic.

According to Newton’s law of gravitation,

Gravitational force is: $F = \frac{G m_{1} m_{2}}{r^{2}}$

Contact Forces

This force is applied by objects when they are in contact with each other. This force acts on a point of direct contact between the two objects. Contact force is governed by Newton’s Laws. These forces act in random directions which can be resolved in two components along the surface and are normal to it.

Friction Force

The component of contact force which is parallel to the surface is called Friction Force. Friction force is exerted by a surface to stop the relative motion of between two surfaces.

Normal Force

The component of contact force which is perpendicular to the surface is called Normal Force. The normal force is also called the Support force.

Attachment to Another Body

Tension in the string and spring force comes under this category. Let’s learn more about these two forces one by one in detail.

Tension

When a string or a rope is being pulled on both ends, then its resistance against any change in its original composition is called tensile force or tension.

Spring Force

Spring force formula is given by Hooke’s Law,

F=-kx

Here,

F = Force by the spring (N)

K = Spring constant (Nm^-1)

X = displacement of spring from its equilibrium position (m)

Practice Problems of Force

Question 1. Find the gravitational force between two objects of mass 1 Kg each. They are separated by distance of 1 m ?

Answer:

Given Data:

m₁=1 Kg

m₂=1 Kg

$F = \frac{G m_{1} m_{2}}{r^{2}} F = \frac{6.67 \times 10^{- 11} \times 1 \times 1}{1^{2}} F = 6.67 \times 10^{- 11} N$

Therefore, gravitational force between two objects is 6.67 x 10^-11 N

Question 2. A contact force of 10 N is acting on the block at an angle of 37o with respect to horizontal. Find a friction force component.

Options: A) 10 N B) 8 N C) 49N D) 6 N

Answer: (B)

Friction force is the horizontal component of contact force.

So, Friction force=contact force cos(37)

Friction force= $10 \times \frac{4}{5}$

Friction force=8 N

Question 3. A spring has a natural length of 20 cm hinged in a vertical position. If it is loaded with 2 Kg, it gets stretched by 5 cm. Compute its spring constant?

Solution

Here 2 Kg is balanced by spring force.

So Spring force=weight

$k x = m g k = \frac{m g}{x} k = \frac{2 \times 10}{0.05} k = 400 N m^{- 1}$

Question 4. Spring is stretched by 10 N force from both ends. If the spring constant is 50 Nm-1. Then what will be the elongation in spring from its natural length?

Answer:

Force in spring is, F=10 N

Spring Constant, k=50 Nm-1

F=kx

FAQs of Force

Question 1. How to find the direction of the tension force?
Answer: Tension force is always pulling in nature. So it always acts away from the tied ends.

Question 2. What is contact force?
Answer: This force is applied by objects when they are in contact with each other. This force acts on a point of direct contact between the two objects.

Question 3. Name the two components of contact force?
Answer: Normal force and friction force are two components of contact force.

Question 4. Explain non-contact forces?
Answer: A non-contact force is a force applied to an object by another body that is not in direct contact with it.

NCERT Class 11 Physics Chapters

Physical World	Units and Measurements	Motion in a Straight Line
Motion in a Plane	Laws of Motion	Work Energy and Power
Particles and Rotational Motion	Gravitation	Mechanical Properties of Solids
Mechanical Properties in Liquids	Thermal Properties of Matter	Thermodynamics
Kinetic Theory	Oscillations	Waves