What is Newton’s Second Law of Motion? [Easy Explanation]

What is Newton's Second Law of Motion? [Easy Explanation]

Why is it easy to move this stone?

Newton's Second Law of Motion Example Picture

Why it is difficult to move this stone?

You might be thinking that it’s a simple question !!

Stone moves easily, as some force is given to it.

But what about the second case, why the stone is not moving easily?

The answer is simple !!

Because of its large size, the stone is not moving easily.

In short, the acceleration of stone depends upon both force as well as mass.

That’s all you need to understand in Newton’s second law of motion.

Newton’s second law of motion states that:

“The acceleration is directly proportional to net force applied and inversely proportional to mass of the object”

Newton’s second law examples

You have definitely not understood the above statement of Newton’s second law, right?

Well, I know such statements are difficult to understand and make your mind confused.

Don’t worry, Let’s make it simple.

I have explained some real life examples of Newton’s second law of motion which are mentioned below.

From these examples, you will surely get the exact idea about what newton’s second law actually means.

Okay, So let’s see the examples one by one…

The Car

How would you feel when you are going somewhere and your car gets damaged?

The same thing happened with one boy and his dad in this example.

In order to start the car, the boy pushes the car but it doesn’t work.

See this,

Example of Newton's second law of motion in which man is looking at small Boy which is pushing a car

Do you have any idea how Newton’s second law is applied here?

The answer is simple.

A boy is applying force to the car but because of its large mass, it doesn’t accelerate easily.

In short, acceleration of the car is inversely proportional to its mass.

Now, how will this car accelerate further?

As you can see this car is accelerating easily when some guys are helping them.

Example of Newton's second law of motion in which man is looking at some boys which is pushing a car

Why did this happen?

Here, the force acting on the car is more compared to one single boy.

Because of this reason, the car accelerates further easily.

It means that these guys together give more impact compared to one single boy.

In short, acceleration of the car is directly proportional to the net force applied on it.

Conclusion, 

In both cases, forces are acting on the car.

But in the second case, the force acting on the car is more and so the car accelerates further easily.

Therefore, acceleration depends upon both mass as well as force.

And this thing indicates Newton’s second law of motion.

(Acceleration is directly proportional to the net force applied on the object and inversely proportional to its mass)

A horse

Example of Newton's second law of motion in which orange horse is pulling a horse cart

As you can see, one horse is pulling the cart.

When one single horse is pulling the cart, the cart is not accelerating further easily.

(As the mass of the cart is more, it requires more force in order to accelerate further easily)

It means, it’s not possible for one single horse to pull the cart.

So in this case, acceleration of the cart is inversely proportional to its mass.

Now, see what happens…

Example of Newton's second law of motion in which one boy and some  horses are pulling a horse cart

The cart accelerates further easily when two or three horses pull it together.

The reason behind this is,

Whatever force exerted by two to three horses is very large compared to force exerted by one single horse.

So,

In this case, acceleration of the cart is directly proportional to the net force applied to it.

(More the force applied on the cart, the more it will accelerates further easily)

Conclusion,

In both cases, horses are pulling the cart.

In the first case, it’s not easy for a single horse to pull the cart.

Whereas in the second case, 

As two to three horses pulls the cart together, the cart accelerates further easily.

In short,

Acceleration depends upon both mass as well as force which shows the presence of newton’s second law of motion.

The Ball

Do you know how Newton’s second law of motion works when you simply hit the cricket ball by bat?

Simply think,

What happens when a football is given to the player instead of a cricket ball?

See this,

Newton's 2nd law of motion example of base ball player hitting a football

As the football has more mass, the player has to apply more force by the bat.

So in this case, acceleration of football is inversely proportional to its mass.

Therefore, football doesn’t accelerate further easily.

Now when a cricket ball is given to the player instead of football, with less amount of force the ball easily travels to a longer distance.

Newton's 2nd law of motion example of base ball player hitting a tennis ball

Here, the player doesn’t have to apply a large amount of force in order to hit the ball.

(As the mass of the cricket ball is very less compared to football)

Therefore, acceleration of a cricket ball is directly proportional to the net force applied on it.

Conclusion,

In both cases, the player hits the ball.

In the first case, it’s not easy for the football to accelerate at a longer distance. 

(Player has to apply more force, as the mass of the football is more)

But in the second case, a cricket ball easily accelerates further with less amount of force.

(As the mass of the cricket ball is very less compared to football)

In short, Acceleration depends upon both mass as well as force.

Which indicates the presence of Newton’s 2nd law of motion.

Condition in Newton’s 2nd Law of motion

Condition for balanced forces in Newton's 2nd law of motion

You already know,

According to Newton’s first law of motion,

If the forces are balanced, then there will be no acceleration of the object.

Newton has already mentioned in his first law that objects will only accelerate if an unbalanced force acts on it.

(Object at rest remains at rest and object motion remains in motion)

Now, Newton’s 2nd law of motion is all about how much the body will accelerate.

And you already know,

Acceleration of any object will take place only if an unbalanced force acts on it.

Condition for unbalanced forces in Newton's 2nd law of motion

Newton’s 2nd law of motion states two things:

  • Acceleration of the object directly depends upon the net force applied to it.

(i.e. If the net force on the object increases, then there will be an increases in its acceleration)

At the same time,

  • Acceleration of the object inversely depends upon the mass of the object.

(i.e. If the mass of the object increases, then there will be a decrease in its acceleration)

What are the directions of F and a?

As already discussed in the above section, 

The acceleration of objects will take place only if an unbalanced force acts on it.

That’s why, according to Newton’s second law, 

“The acceleration is directly proportional to net force applied and inversely proportional to mass of the object”

But, if we talk about the directions of the net force and acceleration, then?

Are they having the same directions? (or different?)

To understand these simple questions, let’s take one simple example.

See this,

Water truck

Example of animated water truck in Newton's 2nd law of motion

You have definitely seen the water truck going on the road.

Now tell me one thing, 

What will be the direction of the force and acceleration? (when this truck is moving on the road)

Are both the force and acceleration having the same directions?

Maybe these types of questions have surely not come into your mind, right?

Don’t worry,

From the below tests, you’ll get the exact idea about the directions of force and acceleration.

Test #1 What are the directions of F and a?

Animated water truck showing directions of force and acceleration in Newton's 2nd law of motion

You can see clearly the water dropped on the road, as the water truck moves forward on the road.

So, what can you say about the directions of force and acceleration?

A) Both are having opposite directions

B) Both are having forward directions

C) Both are having backward directions

D) None of these

Answer

Test #2 What are the directions of F and a?

Newton's 2nd law of motion example of animated water truck showing directions of force and acceleration

In this case, the water is slowly dropping onto the road.

But, the water truck driver applies a brake.

What are the directions of force and acceleration in this case? (when the water truck driver applies a brake)

A) Both are having opposite directions

B) Both are having forward directions

C) Both are having backward directions

D) None of these

Answer

Conclusion is,

Both the net force and acceleration have the same directions.

In whichever direction the force acts, acceleration will also take place in that direction only.

(Direction of the net force is always in the direction of acceleration)

Newton’s 2nd Law – Misconception

If you have read the above section completely, then it’s easy to remember Newton’s second law of motion.

You can even speak this law word to word, right.

Now the point is,

What you believe is important, how well you have understood, doesn’t matter.

If you have read Newton’s first law,

You already know, the object will change its behaviour only if an external force acts on it, right.

(This external force is nothing but an unbalanced force only)

Now the question is,

In order to keep the object moving, external force should be given continuously?

You might be thinking, the answer is YES, right?

If you are thinking so, then you are wrong.

That’s why, You need to first clear this misconception. 

Man confused about the misconception in Newton's second law of motion

The most common misconception that people used to believe from the ages,

External force is needed to be given continuously on the object. (To keep it’s motion continue)

Are you believing the same? (Let me know in the comments)

There is one similar big Misconception in Newton’s third law which we’ll see it later.

Clear this misconception (Right Now)

Even today, people still believe this misconception that…

External force is needed to be given continuously on the object. (To keep it’s motion continue)

If you still have some doubts or any kind of misconception left in your mind, 

Don’t worry.

Let’s clear this Misconception, by considering some basic examples mentioned below.

(Also change your belief system)

The Ball

Example of blue football moving with uniform motion in Newton's second law of motion

Consider this ball is moving with uniform speed.

Now the question is,

Does any external force is required to keep this ball moving forward? (If the friction and air resistance are neglected)

Example of blue football in Newton's second law of motion

What can you say about the ball?  (If no external force is given to the ball)

A) Speed of the ball increases slowly

B) Speed of the ball decreases slowly

C) Ball will continue its motion (with same speed, in the same direction)

D) None of these

Answer

The Book

Loki and Sara were the two good friends.

Once, both of them are discussing the topic of one book.

Before going in detail, tell me one thing…

What if the book is simply lying on the floor, is it balanced or unbalanced?

Obviously Yes, right. (The book is in balanced condition)

See this,

Balanced forces acting on old book in Newton's second law of motion

As mentioned in Newton’s first law, the object will not change its behaviour unless an unbalanced force acts on it.

Now what if this book is in motion?

Does any external force is required to keep this book moving forward? (If the friction and air resistance are neglected)

Example of book in Newton's second law of motion

The same question Sara asks Loki, while discussing the topic of the book.

Sara tells Loki that the book will start moving in the horizontal direction.

(If there is no air resistance or some kind of friction acting on the book)

In short,

Sara believes that the book could also have a motion in the horizontal direction.

But,

Loki believes that the object can not move in the horizontal direction. (If only vertical forces are acting on it)

Loki believes that the book will remain in rest position only.

Both of them are having different belief systems.

According to you, who do you think has the right belief system?

A) Loki is correct

B) Sara is correct

C) Sara and Loki both are correct

D) None of these

Answer

Toy Car

Example of animated boy playing with toy car in Newton's second law of motion

Have you played with the toy car in your childhood like this?

Obviously yes, right.

All of us have played like this in our childhood.

Now you already know, 

When the boy releases the car from his hand, the car starts moving forward in the horizontal direction.

In short, when the boy releases the car, the car comes in the motion.

Now the question is,

Imagine, if there was no friction along the level surface and there was no air drag to pull the car forward.

Example of small child playing with toy car in Newton's second law of motion

Does any external force is required to keep this car moving forward? (If the friction and air resistance are neglected)

What do you think of this car, how long the car will travel further?

A) Car travels forever with the uniform speed

B) Car immediately stops

C) Car’s speed slowly increases

D) None of these

Answer

Conclusion 

If you have read all the above cases, one thing is common.

Objects can have motion in the horizontal direction. 

It means objects can move in the horizontal direction even if only vertical forces are acting on them.

Let’s make it simple.

What happens when a boy is moving on a skateboard with uniform speed, still an external force is required to keep a skateboard moving?

Will this skateboard keep moving forever?

Red animated boy moving on a black skate board with uniform motion in Newton's second law of motion

In short, External force is not needed to be given continuously on a skateboard to keep its motion continue.

(A skateboard moving with uniform motion will continue moving forward)

A force is not needed to be given on the object continuously, to keep its motion continue.

Example of flying eagle in newton's second law of motion

Always Remember,

External force is not needed to produce the motion of any object.

External force only helps in accelerating the object forward.

(Object will not change its behaviour, if no external force is given to it)

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Don’t you think, is easy to remember the statement of Newton’s second law of motion?

(Let me know by leaving a comment)

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