Newton’s Second Law of Motion [Simple Definition + Examples]

What is Newton's Second Law of Motion? [Simple Definition + Example]

Newton’s second law is all about understanding the acceleration of an object.

That’s it.

Here’s newton’s second law of motion simple definition:

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

I know you have not understood the above definition.

Don’t worry, I’ll make it easy for you.

Let’s consider some Everyday Life examples to understand the above statement properly.

Newton’s Second Law Examples in Everyday Life

Here’s a list of Everyday Life examples of newton’s second law:

  • Pushing a car: Small child vs Two boys
  • Pulling a horse cart: One horse vs Three horses
  • Hitting a ball with the bat: Tennis ball vs Football
  • Lifting a courier box: Large vs Small
  • Riding a bicycle: Two persons vs One person
  • Pushing a trolley: Heavy weight vs Light weight
  • And more…

Let’s understand each one of these examples with pictures. (So you’ll get an exact idea)

#1 Pushing a car: Small child vs Two boys

Newton's second law example - Pushing a car

This is how newton’s second law works, while pushing a car.

When a small child pushes a car… Because of less force, a car does not accelerate forward easily.

When two boys together push a car… Because of more force, a car accelerates forward easily.

It means that… Acceleration is directly proportional to force applied on an object.

(More the force applied on an object, the more it will accelerate)

This thing shows the presence of newton’s second law of motion.

#2 Pulling a horse cart: One horse vs Three horses

Example of newton's second law - Pulling a horse cart

This is how newton’s second law works, while pulling a horse cart.

When one horse pulls a horse cart… Because of less force, a horse cart does not accelerate forward easily.

When three horses together pull a horse cart… Because of more force, a horse cart accelerates forward easily.

It means that… Acceleration is directly proportional to force applied on an object.

(More the force applied on an object, the more it will accelerate)

This thing shows the presence of newton’s second law of motion.

#3 Hitting a ball with the bat: Tennis ball vs Football

Newton's second law of motion example - Hitting a ball with the bat

This is how newton’s second law works, while hitting a ball with the bat.

When a man hits a tennis ball… Because of less mass, a tennis ball accelerates forward easily.

When a man hits a football… Because of more mass, a football does not accelerate forward easily.

It means that… Acceleration is inversely proportional to mass of an object.

(More the mass an object has, the less it will accelerate)

This thing shows the presence of newton’s second law of motion.

#4 Lifting a courier box: Large vs Small

Example of newton's second law of motion - Lifting a courier box

This is how newton’s second law works, while lifting a courier box.

When a courier boy lifts a large box… Because of more mass, a box does not accelerate forward easily.

When a courier boy lifts a small box… Because of less mass, a box accelerates forward easily.

It means that… Acceleration is inversely proportional to mass of an object.

(More the mass an object has, the less it will accelerate)

This thing shows the presence of newton’s second law of motion.

#5 Riding a bicycle: Two persons vs One person

Newton's second law example in everyday life - Riding a bicycle

This is how newton’s second law works, while riding a bicycle.

When two girls are riding a bicycle… Because of more mass, a bicycle does not accelerate forward easily.

When one boy is riding a bicycle… Because of less mass, a bicycle accelerates forward easily.

It means that… Acceleration is inversely proportional to mass of an object.

(More the mass an object has, the less it will accelerate)

This thing shows the presence of newton’s second law of motion.

#6 Pushing a trolley: Heavy weight vs Light weight

Newton's second law explained - Pushing a trolley

This is how newton’s second law works, while pushing a trolley.

When a boy pushes a heavy weight trolley… Because of more mass, a trolley does not accelerate forward easily.

When a boy pushes a light weight trolley… Because of less mass, a trolley accelerates forward easily.

It means that… Acceleration is inversely proportional to mass of an object.

(More the mass an object has, the less it will accelerate)

This thing shows the presence of newton’s second law of motion.

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There are so many other examples of newton’s second law that we are experiencing in our everyday life.

Newton’s Second Law Equation/Formula

Here are the three equations of newton’s second law:

  1. Fnet = ma

Where, 

Fnet = net force applied on an object, N

m = mass of an object, m

a = acceleration of an object, m/s2

  1. p = mv

Where, 

p = momentum of an object, kg m/s

m = mass of an object, m

v = velocity of an object, m/s

  1. Fnet = m(v-u)/t

Where, 

Fnet = net force applied on an object, N

m = mass of an object, m

(v-u) = rate of change in momentum, kg m/s2

mv = final momentum of an object, kg m/s

mv = initial momentum of an object, kg m/s

v = final velocity of an object, m/s

u = initial velocity of an object, m/s

t = time, s

Let’s solve some problems based on these equations.

Newton’s Second Law Problems

Problem 1: One ball having a mass of 4 kg accelerates forward at the rate of 9 m/s2. Calculate the amount of net force applied on a ball.

Solution:

Given data:

Mass of a ball, m = 4 kg

Acceleration of a ball, a = 9 m/s2

Net force applied on a ball, Fnet = ?

According to newton’s second law equation,

Fnet = ma

Fnet = 4 × 9

Fnet = 36 N

Therefore, the net force applied on a ball is 36 N.


Problem 2: A bicycle accelerates forward at the rate of 4 m/s2, when a force of 10 N is applied on it. Calculate the mass of a bicycle.

Solution:

Given data:

Acceleration of a bicycle, a = 4 m/s2

Net force applied on a bicycle, Fnet = 10 N

Mass of a bicycle, m = ?

According to newton’s second law equation,

Fnet = ma

10 =  m × 4

m = 2.5 kg

Therefore, the mass of a bicycle is 2.5 kg.


Problem 3: Calculate the momentum of a roller which is moving forward with a velocity of 4 m/s. Consider the mass of a roller as 2 kg.

Solution:

Given data:

Velocity of a roller, v = 4 m/s

Mass of a roller, m = 2 kg

Momentum of a roller, p = ?

According to newton’s second law equation,

p = mv

p = 2 × 4

p = 8 kg m/s

Therefore, the momentum of a roller is 8 kg m/s.


Problem 4: When a stone having a mass of 5 kg is thrown from a hill, it gains the momentum of 60 kg m/s. With what velocity a stone strikes on the ground?

Solution:

Given data:

Mass of a stone, m = 5 kg

Momentum of a stone, p = 60 kg m/s

Velocity of a stone, v = ?

According to newton’s second law equation,

p = mv

60 = 5 × v

v = 12 m/s

Therefore, a stone strikes on the ground with a velocity of 12 m/s.


Problem 5: One truck having a mass of 975 kg is initially at rest. In 20 seconds, a truck attains the velocity of 40 m/s. Calculate the amount of net force acting on a truck.

Solution:

Given data:

Mass of a truck, m = 975 kg

Time, t = 20 seconds

Final velocity of a truck, v = 40 m/s

Net force acting on a truck, Fnet = ?

According to newton’s second law equation,

Fnet = m (v-u)/t

Fnet = 975 (40 – 0)/20

Fnet = 975 × 2

Fnet = 1950 N

Therefore, a net force of 1950 N is acting on a truck.


Problem 6: A 300 grams skateboard is moving forward with the initial velocity of 110 m/s. When a skateboard strikes with an obstacle, an opposing force of 5 N acts on it. The speed of a skateboard decreases and reaches to 10 m/s. After how much time, a skateboard will come into rest position?

Solution:

Given data:

Mass of a skateboard, m = 300 grams = 0.3 kg

Initial velocity of a skateboard, u = 110 m/s

Opposing force acting on a skateboard, Fnet = – 5 N

Final velocity of a skateboard, v = 10 m/s

Time, t = ?

According to newton’s second law equation,

Fnet = m (v-u)/t

– 5 = 0.3 (10 – 110)/t

– 5 = 0.3 (- 100)/t

– 5 = – 30/t

5t = 30

t = 6 seconds

Therefore, a skateboard will come into rest position after 6 seconds.

Summary

From the above examples, one thing is understood.

More the force applied on an object, the more it will accelerate.

Similarly,

More the mass an object has, the less it will accelerate.

That’s how you can easily remember the simple definition of newton’s second law:

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

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What do you think, is it easy for you to understand this concept of newton’s second law?

(Let me know in the comments below)

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