Push and Pull

Newton’s Laws of Motion tell us three things about how and why things move.

Law of motion #1: An object will remain at rest until an outside force puts it in motion. Force is the push or pull that starts something moving.

Law of motion #2: The speed at which an object moves depends upon the amount of force used to move the object. The weight of an object also determines how it responds to the force being used to move it.

Law of motion #3: For every action or act of force, there is an equal and opposite reaction.

Newton’s laws have been able to answer many questions in the world of science for centuries, but sometimes it is hard to see how the laws of motion work.

EXAMPLE: Let’s say you are helping your mom put groceries in the car, but when you take your hand off the grocery cart to lift the bags of groceries out, the cart starts rolling away. You didn’t push it, and the wind isn’t blowing, so what happened? Gravity—that’s what.

Gravity is nature’s force that holds things down. Gravity keeps everything from floating out into space. Gravity is always pulling us down. So if the cart is not setting on a level surface, gravity is going to pull it to the lowest point. Gravity is also the reason we always come back down when we jump up in the air.

Testing Newton’s laws

Let’s try a few things to see how the laws of motion work.

Here is what you need:

• Cotton ball
• Ping pong ball
• Tennis ball
• Large ball-soccer, basketball, or volleyball
• Spoon-the kind you eat your cereal with
• Drinking straw
• Pencil
• Flat surface
• Open area
• Small hill outside OR make a small incline with board and some books or bricks
• Pen and paper

Here is what you do:

• Place one object at a time on the flat surface , blow on it until it begins to move
• When it stops, mark the stopping point with a piece of tape (optional)
• Repeat this process until you have moved all 7 items
• Standing in an open area, throw each of the objects one at a time with the same amount of force
• Mark the spot at which each one drops with a piece of tape (optional)
• Standing at the top of the hill or sitting at the top of the incline you built, place each ball—one at a time—at the top of the incline and let it go
• Count how long it takes for each one to get to the bottom or to stop

What happened:

• Which items rolled the farthest when you blew them?
• Which items went the farthest when you threw them?
• Which ball rolled the farthest?
• Which ball rolled the fastest?

Take another look at Newton’s laws. Now can you see how they work?