Okay, let’s make this simple.

Did you ever wonder, what makes an object to slow down or to move faster, or change its direction of motion?

For example,

What do you do to make this ball **move?**

What do you do to make this moving ball **move faster?**

What do you do to make this moving ball **stop?**

What do you do to **change the direction** of this moving ball?

In all the above situations, a force is required…

To make the ball move.

To make the moving ball move faster.

To make the moving ball stop.

To change the direction of the moving ball.

In other words,

**With the help of a force,** the ball is either made to move faster or slower or its direction of motion is changed.

In fact,

Sometimes we often say that a force has been applied on an object when it is kicked, pushed, pulled or thrown.

But the question is, **what is force?**

What force do to objects on which it is applied?

You’ll get all the answers here.

## Definition of force

A force can be simply defined as follows:

*“A force is a push or pull on an object”*

That’s the simple definition of force in physics.

A force always occurs when **at least two objects** must interact with each other.

In other words,

An interaction of one object with another object results in a force between the two objects.

### Force formula

A force is the product of mass and acceleration.

The symbol and formula of force are as follows:

**Symbol of force:****F**

**Formula of force: F = ma**

Where,

F = force

m = mass

a = acceleration

### Unit of force

The CGS (centimetre gram second) unit of force can be given as follows:

**CGS unit of force: dyne (dyn)**

The SI (system international) unit of force can be given as follows:

**SI unit of force:****Newton (N)**

The amount of force required to accelerate an object of mass 1 kg at the rate of 1 m/s^{2} is known as 1 Newton.

**1 Newton = 1 kg m/s**^{2}

The dimensional formula of force is given as follows:

**Dimension formula of force:****M**^{1}L^{1}T^{-2}

Where,

M = mass

L = length

T = time

To remember in an easy way, refer to the table mentioned below.

1. | Symbol of force: F |

2. | Formula of force: F = ma |

3. | CGS unit of force: dyne (dyn) |

4. | SI unit of force: Newton (N) |

5. | 1 Newton = 1 kg m/s^{2} |

6. | Dimensional formula of force: M^{1} L^{1} T^{-2} |

## Forces are due to an interaction

As discussed in the definition of force,

At least two objects must interact with each other for a force to occur.

You might be thinking, HOW?

Let’s find out.

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Suppose that one boy is standing in front of the football.

Will the football move on its own, due to his presence?

Now, suppose the boy kicks the football. (i.e., he applies a force on the football)

The football starts moving in the direction of force applied.

In short,

The boy has to apply a **force** on the football to make it move from the rest position.

As you can see, the football moves from its position only when the boy kicks the football.

It means that,

Whenever both the boy and the football comes in contact with each other, a force results in between them.

Therefore,

*At least two objects** must interact with each other for a force to occur.*

Let’s take more examples.

Form the below images, can you decide who is pulling and who is pushing?

Can you guess, **who is pushing whom?**

Yes, you guessed the right answer !!

Here, both the bulls are pushing each other.

In other words, both of them are applying forces on each other.

Can you guess, **who is pulling whom?**

Again, here also both the girls are pulling each other.

It means that both the girls are applying forces on each other.

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From the above examples,

It is clear that **at least two objects** must interact with each other for a force to occur.

(i.e., Interaction of one object with another object results in a force between the two objects)

Therefore, force always occurs due to an interaction between at least two objects.

## Examples of force in everyday life

Actions like pulling, pushing, kicking, lifting, hitting, opening, picking, closing etc. are often used to describe certain tasks.

For example,

- Pulling the cart

- Pushing the trolley

- Kicking the ball

- Lifting the dumbbells

- Hitting the punching bag

- Opening a window

- Picking a glass of water

- Closing the door

All these different tasks are the examples of force.

Each of these tasks results in some kind of change in motion of an object.

And to perform each of these tasks, a **force** is must required.

Let’s understand this practically. (One by One)

### Pulling the cart

Have you seen a horse pulling the cart? (maybe you have seen it in a movie)

Suppose that the cart has to travel some distance. How will it move further?

Will the cart move on its own, due to the presence of a horse?

Obviously NO, right.

A horse has to pull the cart, in order to move the cart further.

(i.e., A horse has to apply a force to move the cart further)

It means that, A **force** is required to pull the cart.

### Pushing the trolley

Suppose that a heavy trolley having a luggage is placed on the floor in your home.

Now, you have to move this heavy trolley from one place to another place.

How will you move the trolley further?

You must have to push it or pull it, right.

*(unless you push or pull the trolley, the trolley will not move from its position)*

In other words,

A **force** is the only thing that changes the position of the trolley.

### Kicking the ball

Have you made any goal by kicking the ball? (maybe you have made it in a mobile game…?)

Suppose that you are standing in front of the ball and you want to kick it with your leg.

Will the ball move on its own, just by standing in front of the ball?

Obviously NO, right.

The ball will not change its position unless you kick it with your leg.

Or

The ball will not change its position unless a** force** is applied on it.

### Lifting the dumbbells

If you have gone to the gym, you have definitely seen a set of dumbbells placed on the floor.

Suppose that you want to lift the dumbbells.

How will you lift the dumbbells?

You need some energy to lift the dumbbells.

In other words, you need to apply a **force** to lift the dumbbells.

### Hitting the punching bag

Suppose that you have a punching bag at your home.

If you want to hit the punching bag, then how will you hit it?

You must hit it by yourself, right.

*(you can punch or kick the punching bag, that’s your choice)*

In short, you have to apply a **force** to hit the punching bag.

### Opening a window

Suppose that you wake up early in the morning and you want to open a window of your room.

What will you do to open a window?

You have to push the window with your hands to open it, right.

It means that you have to apply a **force** with your hands to open a window.

### Picking a glass of water

Suppose that you are preparing for your exams in your study room.

Imagine, while studying you want to drink some water from a glass of water placed on the table.

How will you pick the glass of water from the table?

You must have to use your hand to pick the glass of water, right.

In other words, you have to apply a **force** with your hand to pick the glass of water.

### Closing the door

Suppose that you are coming from the market to your home.

After coming inside the home, you should close the door of your home, right?

How will you close the door of your home?

It’s simple.

By giving a little push to the door, you can close it.

In other words, you have to apply a **force** to close the door.

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From all the above examples of forces it is clear that,

In order to move an object, it has to be pushed or pulled.

Therefore,

In physics, a force is defined as a push or a pull on an object.

Can you guess any other example of force? (Let me know in the **comments**)

## What are the effects of force?

Sr No. | Effects of force |
---|---|

1. | A force can change the shape and size of an object |

2. | A force can make an object move from rest |

3. | A force can stop the moving object |

4. | A force can change the speed of the moving object |

5. | A force can change the direction of the moving object |

All of these are the effects of force.

Let’s understand the above mentioned effects of force practically. (One by One)

### A force can change the shape and size of an object

Do you know how a force can change the shape and size of an object?

Simply think, what happens when a heavy weight is placed on a spring?

In other words,

What happens when a force is applied on a spring?

See this,

Here you can see,

When a heavy weight is placed on a spring, the shape and size of a spring gets changed.

What does it mean?

It means that,

When a heavy weight is placed on a spring, a force is applied on a spring in the downward direction.

*(This force changes the **shape as well as the size** of a spring)*

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Think,

What happens when you press a rubber ball placed on a table?

What happens when an inflated balloon is pressed by placing it in between your palms?

What happens to the shape of a ball of dough when it is rolled to make a chapati?

In all the above situations,

*A **force** is the only thing that changes the **shape and size **of an object.*

### A force can make an object move from rest

How can you make an object move from rest?

Let’s take one example.

Suppose that there are some garbage bags near your home.

Everyday a dustman (garbage collector) comes near your home to pick these garbage bags.

Note that these garbage bags are **initially at rest**.

Have you ever wondered, what changes the position of garbage bags when a dustman picks it with his hands?

See this,

As you can see,

A dustman has to apply a force to pick up these garbage bags.

In other words,

A force is the only thing that changes the position of these garbage bags.

*(This force makes the garbage bags **move** from rest)*

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Think,

How can you make your science book move, which is placed on a table at rest?

How can you make your school bag move, which is initially at rest?

How can you make your laptop or computer move, which is initially at rest?

In all the above situations,

*A **force** is the only thing that makes an object **move** from rest.*

### A force can stop the moving object

Do you know how a moving object can be stopped?

Suppose that you are playing a football match and you kicked the football towards a goalkeeper.

How will a goalkeeper stop the moving football coming towards him?

A goalkeeper must have to apply a force to stop the moving football, right?

See this,

When a goalkeeper uses his hands to stop the football, a moving football stops.

What does it mean?

It means that,

A goalkeeper applies a force on the moving football with his hands to stop the football.

*(This force **stops** the moving football coming towards him)*

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Think,

How can a moving car be stopped?

How can a moving train be stopped by the train driver at different stations?

How can a moving bike be stopped?

In all the above situations,

*A **force** is the only thing that **stops** the moving object.*

### A force can change the speed of the moving object

Do you know how a force can change the speed of the moving object?

It’s simple.

Imagine, you are riding a bicycle on an empty road.

Suppose that you want to increase the speed of your bicycle.

What will you do to increase the speed of your bicycle?

You must have to apply some force to the paddle of your bicycle, right?

See this,

Similarly,

What will you do, if you want to decrease the speed of your bicycle?

You have to apply the brakes, right.

Again, the speed of your bicycle changes due to a force.

So, doesn’t matter if the speed of your bicycle is high or low,

A force is the only thing that changes the **speed** of your bicycle.

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Think,

What increases the speed of a stone falling from a height?

What decreases the speed of a ball when you throw up in the air?

What increases or decreases the speed of a flowing water?

In all the above situations,

*A **force** is the only thing that changes the **speed **of the moving object.*

### A force can change the direction of the moving object

Have you seen a baseball player hitting a ball?

If you have noticed, the direction of a baseball changes when a player hits the ball with a bat.

Do you know what changes the direction of a baseball?

See this,

As you can see,

When a baseball player hits the ball, the direction of the ball changes.

In other words,

A baseball player applies a force on the ball with the bat.

*(This force changes the **direction** of the baseball)*

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Think,

Why does a carrom striker change its direction, when it touches the edges of the carrom board?

Why does the direction of a smoke change, when you blow air on it from your mouth?

Why does the direction of a hot air balloon change, when it goes up higher in the air?

In all the above situations,

*A **force** is the only thing that changes the **direction** of the moving object.*

## Always remember

After reading the above examples, you have properly understood the effects of force.

BUT, it is important to remember that,

None of the above effects takes place if there is no action of force.

In short, **without the action of force,**

Objects cannot move by itself.

Objects cannot change speed by itself.

Objects cannot change direction by itself.

Objects cannot change their shape by itself.

## Types of forces

Forces can be divided in two types: Contact forces and Non-contact forces.

Let’s understand the definition of different types of forces.

### Contact forces

**Contact force:** A force that acts when two objects are physically in contact with each other is known as contact force.

The following are the different types of contact forces:

**Muscular force****: **A force resulting due to an action of muscles is known as muscular force.

**Frictional force****:** A force generated by two surfaces when they slide against each other is known as frictional force.

**Tension force****: **A force generated when a wire, rope or a string is pulled from its opposite ends is known as tension force.

**Applied force****: **A force which is applied to an object by another object or a person is known as applied force.

**Normal force****: **A force which is normal (perpendicular) to the surface of an object is known as normal force.

**Air resistance force****: **A force that acts in the opposite direction on an object when it travels through the air is known as air resistance force.

**Mechanical force****: **A force that produces a change in state of an object (state of rest or state of motion) is known as mechanical force.

**Spring force****: **A force exerted by the spring on an object when it is compressed or stretched is known as spring force.

### Non-contact forces

**Non-contact force:** A force that acts when two objects are not physically in contact with each other is known as non-contact force.

The following are the different types of non-contact forces:

**Magnetic force****:** An attractive or repulsive force between the poles of a magnet and electrically charged moving particles is known as magnetic force.

**Gravitational force****:** Every object in the universe, whether small or large, exerts a force on every other object. This force is known as gravitational force.

**Electrostatic force****:** An attractive or repulsive force between the two electrically charged particles is known as electrostatic force.

To understand in detail,

**You can check:** Different types of forces (A complete guide)

## A force is a Scalar or Vector quantity?

What do you think, is force a scalar or vector quantity?

Okay, take a look at the definition of scalar and vector quantity.

**Scalar quantity:** A scalar quantity is a quantity which is described only by a magnitude.

**Vector quantity:** A vector quantity is a quantity which is described by both a magnitude and a direction.

If you are thinking that force is a vector quantity, you are right.

Let’s understand this using an example.

Suppose that this guy is applying a force of 2 N to pull his cart.

What does it mean?

It means that when this guy pulls the cart, a force is applied on the cart.

And this force is represented by both magnitude as well as the direction.

(i.e., magnitude of the force is 2 N and direction of the force is along the string, as shown in the figure)

Therefore, **A force is a vector quantity.**

*(As the force has both the magnitude as well as the direction)*

## Force measurement – How force is measured?

Do you know how a force is measured Or what instrument is used to measure a force?

As discussed above, A force is a vector quantity.

It means that a force has both the magnitude as well as the direction.

And the magnitude of a force is measured using the force measuring unit called Newton.

**Force measurement unit: Newton (N)**

But the question is, by using which instrument a force is measured?

Let’s find out.

### Force measuring device – Spring balance

You already know,

Weight is a one type of force due to an earth’s gravitational pull which is acting in the downward direction.

Now to measure this force, an instrument called spring balance is used.

As you know, whatever reading is seen in the spring balance is the weight of an object.

So the question is,

How can you measure a force using the spring balance?

It’s simple.

Look, when you place this spring balance on the floor it shows the **zero reading.**

You know why?

It’s because the gravity pulls the weight downwards. (i.e., Net force, **F = 0**)

Now, when you’ll pull this spring balance with your hand it shows some reading, which is nothing but a force.

That’s how you can measure a force.

### Solved examples of force

According to Newton’s second law of motion,

Force is the product of mass and acceleration.

So, the formula of force is given by, **F = ma.**

Using this formula you can calculate the value of force applied on an object.

Below are some solved examples of force in which you’ll understand how the value of force is calculated.

**Numerical 1:**

How much force is required to accelerate a bicycle at the rate of 7 m/s^{2}, if the mass of the bicycle is 4 kg?

**Solution:**

Here,

Bicycle accelerates at the rate of, **a = 7 m/s ^{2}**

Mass of the bicycle,

**m = 4 kg**

Force required,

**F = ?**

According to formula of force,

F = ma

F = 4 × 7

**F = 28 N**

So, a force of 28 N is required to accelerate the bicycle at the rate of 7 m/s

^{2}.

**Numerical 2:**

A cannon ball of mass 6 kg accelerates further at the rate of 100 m/s^{2}. Calculate the force applied on the cannon ball.

**Solution:**

Here,

Mass of the cannon ball, **m = 6 kg**

Cannon ball accelerates at the rate of, **a = 100 m/s ^{2}**

Force applied,

**F = ?**

According to formula of force,

F = ma

F = 6 × 100

**F = 600 N**So, a force of 600 N is applied on the cannon ball.

**Numerical 3:**

A 12 kg heavy stone falling from the hill accelerates downwards when a force of 60 N is applied on it. At what rate the stone will accelerate downwards?

**Solution:**

Here,

Mass of the stone, **m = 12 kg**

Force applied on the stone, **F = 60 N**

Stone accelerates downwards at the rate of, **a = ?**

According to formula of force,

F = ma

a = F / m

a = 60 / 12**a = 5 m/s ^{2}**

So, the heavy stone accelerates downwards at the rate of 5 m/s

^{2}.

## Summary

Let’s summarize all the main points that you should know about a force.

**Definition of force**

In physics, a force can be defined as follows:

*“A force is a push or pull on an object”*

*(At least two objects must interact with each other for a force to occur)*

**Formula of force**

According to Newton’s second law of motion,

A force is the product of mass and acceleration.

So, the formula of force can be given as: **F = ma**

Where,

F = force

m = mass

a = acceleration

**Unit of force**

The CGS unit of force is: **dyne (dyn)**.

The SI unit of force is: **Newton (N)**.

Where,

1 Newton = 1 kg m/s^{2}

The dimensional formula of force is: **M ^{1} L^{1} T^{-2}**

Where,

M = mass

L = length

T = time

**Effects of force**

The following are the effects of force:

- A force can change the shape and size of an object.

- A force can make an object move from rest.

- A force can stop the moving object.

- A force can change the speed of the moving object.

- A force can change the direction of the moving object.

BUT,

It is important to remember that **without the action of force,**

Objects cannot move by itself.

Objects cannot change speed by itself.

Objects cannot change direction by itself.

Objects cannot change their shape by itself.

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What do you think, is it easy for you to understand this concept of force?

(Let me know in the **comments** below)