###

### Newton's Laws of Motion

**1. Inertia:** An object in motion will stay in motion
and an object at rest will stay at rest, unless acted on by an outside
force.

**2. F=ma:** Acceleration is produced when a force acts on a
mass. More mass causes less acceleration when a consistent force is
applied.

**3. Action/Reaction:** Every action has an opposite and
equal reaction.

__Newton's
Laws Links__

# Newton's Laws of Motion

Isaac Newton defined three laws concerning the behavior of moving
objects in the 1687. These scientific statements help
to explain the nature of matter and space. Newton's first law of motion
is often called the **Law of Inertia**. His second
law shows the **relationship between force and acceleration**. His
third law is often called the **Action-Reaction Law
of Motion**. It is amazing that he was able to formulate these
important laws of motion through his observations so many
years ago.

Some questions you may have are:

- What is the Law of Inertia?
- What is Newton's Second Law?
- What is action-reaction about?

Newton's First Law

Newton's First Law was actually formulated by Galileo many years
previous. It is called the *Law of Inertia* and
states:

**Every object in a state of uniform motion tends to remain in that
state of motion unless an external force is applied
to it.**

Another way of stating this law in more detail is:

- If an object is motionless, it will stay motionless unless acted
upon by some force.
- If an object is moving at a constant speed or velocity, it will
continue at that speed unless acted upon by some force
along the line of motion.
- If an object is moving, it will move in a straight line unless acted
upon at an angle by some force.

The Law of Inertia assumes there is no friction or other resistive
force that can slow down an object. Inertia can be
best demonstrated in outer space.

## Newton's Second Law

The second law is sometimes called the *Law of Dynamics*,
because it concerns forces and what causes objects to move.
It can be stated as:

**The acceleration of an object of constant mass is proportional to
the force acting upon it.**

Acceleration is the changing of the velocity of the object. Usually,
we are talking about the object speeding up. The
word "deceleration" is usually used when the object is slowing down, but
that also is acceleration or changing
of the velocity.

A force is a push or pull on the object. It may pushing in direct
contact or pulling at a distance in the case of gravity.

This law determines the relationship between force, mass and
acceleration, which is

**F = ma**

where:

**F** is the applied force
**m** is the constant mass
**a** is the resulting acceleration
**ma** is **m** times **a**

Note that the force **F** and acceleration **a** are in the
same direction. Since they have a direction, they are
called *vectors*.

What this law says is that while you are applying a force on an
object, it will continue to accelerate or change its velocity.
It also states that the greater the force on an object, the greater the
acceleration.

## Newton's Third Law

Newton's Third Law is sometimes called the *Law of Reciprocal
Actions* or the *Action-Reaction Law*:

**Whenever one body exerts force upon a second body, the second body
exerts an equal and opposite force upon the first
body. **

This is often stated as: "For every action there is an equal and
opposite reaction."

### Pushing against something

Suppose you are push on a wall with a certain force. Since the wall
is stationary, your force is reflected back against
your hands. The force you apply is the same force that is applied to
your hands.

Now if you are wearing roller skates, and you push on the wall with a
certain force, you will move backward as if that
same force was applied to you.

Suppose you push on a large box that is on the floor. If the friction
between the box and the floor is greater than the
force you are applying, then the equal force will be pushing on your
hands. But if the resistive force of friction is less
than your force, the box will slide along the floor. The force on will
be the force you applied minus the force of friction.

### Add Second Law to Third Law

We can also add Newton's Second Law to the Third Law. If you and a
friend are on roller skates or ice skates and facing
each other, and then you push on your friend with a certain force, your
friend will be accelerated backwards according to **F
= ma.** But because of Newton's Third Law, your push causes an equal
opposite push on you. So you will also accelerate
backwards.

The force you apply on your friend is **F = ma**. So, the
acceleration (**a**) of your friend's motion is dependent
on the force you push (**F**) and his or her mass (**m**).

But also, that same force is applied on you. Suppose we call your
mass (**M**) and your acceleration (**A**). Then
since the forces are the same ** MA = ma**. If your weight (or mass)
is twice that of your friend, then your friend would
move back twice as fast as you.

**M = 2m**

**2mA = ma**

**a = 2A**

**Note**: If you weigh twice as much as your friend, then either:

- You should go on a diet,
- You should get bigger friends, or
- You should not push little people around.

### Gravity

The action-reaction law also applies to the force of gravity,
especially combined with Newton's Law of Dynamics. If you
jump off a ladder, the force of gravity will pull you to the Earth
according to **F = mg**, where **m** is your mass
and **g** is the acceleration due to gravity.

But that same force is working in an opposite direction on the Earth,
pulling it toward you according to **F = MG**,
where **M** is the mass of the Earth and **G** is its
acceleration. Since the mass of the Earth is so much greater
than your mass, its movement is extremely small.

## Summary

Isaac Newton defined his three laws of motion, which are the Law of
Inertia, the Law of Dynamics and the Law of Reciprocal
Actions. These laws can be verified in many common experiments, and they
explain how and why objects move when forces are
applied to them.

Once you work toward a goal, your inertia moves you
toward success