Newton's Laws of Motion.

NEWTON’S LAWS OF MOTION

Have you ever wondered how do elevators work, what is the science to throw a nuclear missile or how can you move a car with one finger? These things are explained by the Three Laws of Motion, published in 1687.

ACTIVITY: Read and learn about Newton’s Laws of Motion, then, answer the questions about the laws at the end of the sheet using the information you just learned.

We’re going to turn to a physicist you’ve probably heard of: Isaac Newton.

With his three laws, Newton outlined his understanding of motion, and a lot of his ideas were totally new.

Today, more than 300 years later, if you’re trying to describe the effects of forces on just about any everyday object -- a box on the ground, a reindeer pulling a sleigh or an elevator taking you up to your apartment -- then you’re going to want to use Newton’s Laws.

Newton’s first law is all about inertia, which is basically an object’s tendency to keep doing what it’s doing. It’s often stated as:

“An object in motion will remain in motion, and an object at rest will remain at rest, unless acted upon by a force”

This is just another way of saying that, to change the way something moves to give it ACCELERATION you need a net force.

http://www.tubechop.com/watch/8837603 (THE VIDEOS ARE AVAIBLE)

So, how do we measure inertia? Well, the most important thing to know is mass. Say you have two balls that are the same size, but one is an inflatable beach ball and the other is a bowling ball. The bowling ball is going to be harder to move, and harder to stop once it’s moving. It has more inertia because it has more mass.

Newton’s second law:

“Net force is equal to mass x acceleration”

Or, as an equation:

“F (net) = m x a”

It’s important to remember that we’re talking about NET force here -- the amount of force left over, once you’ve added together all the forces that might cancel each other out.

http://www.tubechop.com/watch/8837683

Let's say you have a hockey puck sitting on a perfectly frictionless ice rink. And I know ice isn’t perfectly frictionless but stick with it. If you’re pushing the puck along with a stick, that’s a force on it – that isn’t being canceled out by anything else. So the puck is experiencing acceleration. But when the puck is just sitting still, or even when it’s sliding across the ice after you’ve pushed it, then all the forces are balanced out. That’s what’s known as equilibrium.

When we explain by Newton’s third law:

“For every action, there’s an equal but opposite reaction”

This just means that if you exert a force on an object, it exerts an equal force back on you. And that’s what we call the normal force. “Normal” in this instance means “perpendicular” and the normal force is always perpendicular to whatever surface your object is resting on. At least, it is when you're pushing on something big, and macroscopic, like a table.

If you put a book down on a table, the normal force is pushing -- and therefore pointing -- up. But if you put it on a ramp, then the normal force is pointing perpendicular to the ramp. [pic 1]

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Now, the normal force isn’t like most other forces. It’s special, because it changes its magnitude. Say you have a piece of aluminum foil stretched tightly across the top of a bowl, and then you put one lonely grape on top of it. Because of gravity, that grape is exerting a little bit of force on the foil, and the normal force pushes right back, with the same amount. But then you add another grape, which doubles the force on the foil -- in that case, the normal force doubles too. That’ll keep happening until eventually you add enough grapes that they break through the foil. That’s what happens when the normal force can’t match the force pushing against it.

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ACTIVITY: To check your understanding of the 3 laws, there are some questions in the following exercises that you have to answer by using your own words.

1. Who published the three laws of motion?

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1. Define the term “inertia”?

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