# Newton’s Laws of Motion

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Newton’s Laws of Motion

1st 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?

1st 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? = = 8 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 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

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

Let’s Review Newton Once moving at a steady speed In a straight line
It will continue moving At a steady speed 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

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