Newton’s Laws of Motion

1 st Law of Motion An object at rest will stay at rest and an

object in motion will stay in motion (in the same direction and at a constant speed) UNLESS an unbalanced force is applied.

Examples Can you explain these using the 1st Law of

Motion?

1 st Law More simply stated: If they are moving, they want to stay

moving. If they are still, they want to stay still. The only way to change what they are doing

is to apply a force.

Law of Inertia Objects are lazy – they do not want to stop

what they are doing. What can we call this “laziness?”

Inertia Inertia is a measure of it’s resistance to

change. The more resistant, the more inertia Newtons’ First Law is also called the

2nd Law of Motion Usually stated as an equation:

F = ma

What does this mean? And don’t say force equals mass times

acceleration. Anyone can say that, but do you really understand what it means?

What if I restated the equation?

Newton’s 2nd Law Explained

It means the acceleration of an object depends on two things – the mass of the object and the amount of force you apply to change its motion.

Let’s look at this relationship.

Let’s Look Mathematically

If I double the numerator, what happens?

= 4 = 8 4 4

When one variable increases, another variable increases the same amount.

This is called a direct proportion Which 2 variables are directly proportional? What does that mean?

But this is science class!

Math and Science What happens when I increase the

denominator? Let’s try!

4 = 4 =

4 8 This is called an indirect proportion, or inverse

proportion Which 2 variables are inversely proportional? What does that mean?

Newton’s 2nd Law Look at the equation. Think of the

previous fractions. Can you explain what it means now?

2nd Law of Motion The greater the applied force, the faster

the object will move (acceleration).

The more mass an object has, the more force you need to change it’s motion

3 rd Law of Motion For every action, there is an equal and

opposite action.

Let’s ReviewNewton

Once moving at a steady speed In a straight line It will continue moving At a steady speed In a straight line

Once standing still It will stay still

Newton It accelerates in the direction that you

push it If you push twice as hard, it accelerates

twice as much

If it has twice the mass It accelerates half as much

Newton If you push on it It pushes on you

Check out these videos

http://science.discovery.com/interactives/literacy/newton/newton.html

http://www.fmalive.com/

Questions?