# How many Newton’s laws are there?

Let me ask you a question, how many Newton’s laws are there?

Well, the correct answer is 5.

Among these five laws,

Three laws are combined together which is further known to us as Newton’s three laws of motion.

These three newton’s laws of motion are:

• Law I – Newton’s first law of motion
• Law II – Newton’s second law of motion
• Law III – Newton’s third law of motion

And the other two newton’s laws are:

• Law IV – Newton’s law of cooling
• Law V – Newton’s law of universal gravitation

Don’t worry.

I’ll make you understand all newton’s laws with practical examples.

(One by One)

Contents

## Newton’s first law of motion

According to Newton’s first law of motion

“An object at rest remains at rest and object in motion remains in motion unless an unbalanced force acts on it”

Let’s understand the above statement with a practical example, so you’ll get an exact idea.

See this,

If you have you noticed,

When the ball is simply lying on the ground, it will not move on its own.

Even while the ball is in motion, it will not stop on its own.

(If there is no friction along the surface)

In short,

Any object (whether in rest or in motion) will not change its behaviour, unless an unbalanced force acts on it.

That’s all you need to understand in Newton’s 1st law of inertia.

“An object at rest remains at rest and object in motion remains in motion unless an unbalanced force acts on it”

If you want to see more examples of Newton’s first law of motion,

Check out: Real life examples of Newton’s first law

## Newton’s second law of motion

According to Newton’s second law of motion,

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

I know, it’s complicated.

Let’s understand the above statement with a practical example, so you’ll get an exact idea.

See this,

As the stone has less mass, it requires less force to accelerate further.

Therefore,

Acceleration of stone is directly proportional to net force applied on it.

On the other hand,

As the stone has more mass, it requires more force to accelerate further.

Therefore,

Acceleration of stone is inversely proportional to its mass.

That’s all you need to understand in Newton’s 2nd law.

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

If you want to see more examples of newton’s second law of motion,

## Newton’s third law of motion

According to Newton’s third law of motion,

“To every action, there is always an equal and opposite reaction”

Newton has given the statement of the third law of motion in very simple language.

See this,

You have definitely understood the exact meaning of Newton’s 3rd law of motion.

All you need to remember is,

“To every action, there is always an equal and opposite reaction”

That’s all you need to understand in Newton’s 3rd law.

If you want to see more examples of newton’s third law of motion,

Check out: Real life examples of Newton’s third law

## Newton’s law of cooling

According to Newton’s law of cooling

“The rate of heat lost by a body is directly proportional to temperature difference of a body and its surroundings”

So we can write as,

– dQ / dt ∝ ∆T

– dQ / dt = k ∆T

– dQ / dt = k (T2 – T1)

dQ / dt = – k (T2 – T1)

This formula can be used to solve different numericals in Newton’s law of cooling.

Where,

dQ / dt = Rate of heat lost by a body

∆T = (T2 – T1) = Temperature difference between the body and its surroundings

T1 = Temperature of the surroundings

T2 = Temperature of the body

k = positive constant which depends upon the area and nature of the surface of the body

Let’s understand the above mentioned statement of Newton’s law of cooling by considering one practical example.

See this,

As you can see,

When a cup of hot tea is left on the table, it cools down gradually.

Now,

To understand how the body cools down by exchanging heat with the surroundings,

See the graph of temperature vs time mentioned below.

Here, you can see how the temperature of the body falls down w.r.t time.

In short,

Cooling rate of the body keeps on decreasing as the temperature falls down.

Check out: Formula used for newton’s law of cooling

## Newton’s universal law of gravitation

According to Newton’s universal law of gravitation,

“Every particle attracts every other particle in the universe with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers”

In mathematical terms,

Fg ∝ m1 m2

Fg ∝ 1/d2

Therefore,

Fg ∝ (m1 m2) / d2

Fg = G (m1 m2) / d2

Where,

Fg = Gravitational force

G = Universal gravitational constant

m1 , m2 = Masses of the two bodies

d = Distance between their centers

To understand the statement of Newton’s universal law of gravitation,

Let’s take one example.

Consider two balls having mass m1 and m2 as shown in the figure.

Let, d be the distance between their centers.

Now,

According to Newton’s law of gravity,

Both these balls will apply force on each other. (i.e. force of attraction)

See this,

Always remember,

Forces on both the balls have the same value and this force always acts along the line joining them.

The value of force is Fg = G (m1 m2) / d2

Here, G is known as the universal gravitational constant.

It’s value is, G = 6.673 × 10-11 Nm² / kg²

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Don’t you think it is easy to remember all Newton’s laws?

(Let me know by leaving a comment)