Newton's laws of motion

Newton's laws of motion

Newton's first law of motion

States that an object a rest will remain at rest, an object in motion will stay in motion with the same speed and direction unless acted upon by an unbalanced force.

Newton's First Law of Motion

Also known as the law of inertia

Newton's Second Law

Newton's second law relates force, mass and acceleration.

The formula for Newton's second law is

 $F=m\times a$  
Force equals mass times acceleration

Multiple Choice

How much force is necessary to move an object with a mass of 6kg, with and acceleration of 5m/s2?

• 35N

• 20N

• 30N

• 50N

Units for Newton's second law of motion

Force is expressed in Newtons (N)
Mass is expressed in kilograms (kg)
Acceleration is expressed in meter per second squared

 $\frac{m}{s^2}$  

You can also calculate the acceleration of an object when you know the net force and the mass of the object

But what is the net force?

Net force is the total force being applied upon an object.

Net Force

What is the net force in this picture?

• There is a force of 60N being applied to the right and a force of 25N being applied to the left.

What is the net force in this picture?

You have to subtract the force being applied to the left from the force being applied to the right.

Net Force

Therefore, net force is equal to 60N minus 25N

Fnet=35N

Which direction will the box move?

Well, if the force pushing to the right is greater than the one going left, the box will move to the right.

We can also calculate the acceleration of the box using the formula

 $a=\frac{fnet}{mass}\ \ in\ this\ case,\ Fnet=35N\$  and mass = 45kg

Acceleration

so acceleration= net force divided by mass

 $a=\frac{35N}{45kg}\ \ \ \ a=0.78\ \frac{m}{s^2}$  

Open Ended

What's the net force being applied upon the box if there's a force of 70N going to the right, and a force of 60N going to the left?

Open Ended

Is the box moving to the right or to the left?

Open Ended

Now that you know the net force, calculate the acceleration of the box using the formula

 $a=\frac{Fnet}{mass}$  The mass of the box is 5kg.

Newton's Third Law of Motion

States that, for every action, there is an equal and opposite reaction