Newton’s laws of motion

Dynamicslesson 1

1 - Inertia law

A body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

A body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

A body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.

1 - Inertia law

If there is no unbalanced force:

a) The stones will fall anyway

b) The stones will remain steady

Why?

As the inertia law says, a body at rest will remain at rest unless an unbalanced force acts upon it. If there is no unbalanced force, nothing will be expected to happen.

As the inertia law says, a body at rest will remain at rest unless an unbalanced force acts upon it. If there is no unbalanced force, nothing will be expected to happen.

1 - Inertia law

If the paper is pulled out quickly:

a) The coin will fall into the water

b) The coin will follow the paper

Why?

The force is acting on the paper so no change in motion is expected to happen to the coin. It will remain in the same place and then fall as nothing is supporting it.

The force is acting on the paper so no change in motion is expected to happen to the coin. It will remain in the same place and then fall as nothing is supporting it.

2 - Fundamental law

The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body.

The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body.

___ a =

F

m

The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body.

F = m·aI.S. units Newtons (N)

2 - Fundamental law

The apple falls in a way that:

a) Its speed is constant

b) It increases velocity steadily

Why?

As an unbalanced force is acting, a change in the apple’s motion will happen. This change implies a change in its speed. This change is represented by an acceleration (gravity in this case).

As an unbalanced force is acting, a change in the apple’s motion will happen. This change implies a change in its speed. This change is represented by an acceleration (gravity in this case).

2 - Fundamental law

Who reaches the highest acceleration?

a) The elephant

b) The boy

c) Both reach the same

Why?

The force will be bigger for the elephant, but the acceleration will be the same for both!!!

Be careful about that!!

The force will be bigger for the elephant, but the acceleration will be the same for both!!!

3 - Action - reaction law

For every action (Fa) there is always an opposed and equal reaction (Fr).

For every action (Fa) there is always an opposed and equal reaction (Fr).

For every action (Fa) there is always an opposed and equal reaction (Fr).

Fa Fa FrFr

Action and reaction forces act upon different bodies

They can be cancelled!!NOT

3 - Action - reaction law

Who is producing the action force?

a) The girl

b) The boy

c) Both of them

Why?

Actually both of them are performing an action force upon the other. However, two reaction forces appear as a result.

simulation

Actually both of them are performing an action force upon the other. However, two reaction forces appear as a result.

3 - Action - reaction law

To turn right the skier…

a) puts pressure on the left ski

b) puts pressure on the right ski

Why?

The skier performs the action force, but it is the reaction force from the snow which will allow him to turn right.

simulation

The skier performs the action force, but it is the reaction force from the snow which will allow him to turn right.