## Center of Mass and How it Works!

The CENTER OF MASS of an object is the place where all parts balance each other. It is also called the Balancing Point. The Rope Runner balances because its CENTER OF MASS lies at a point directly beneath the rope.

Can you see how the wooden balls help to lower Center of Mass?

Gravity pulls the Rope Runner down toward that point, but the rope holds it up. It would take a lot to tip the Rope Runner over. Can you figure out what would do it?

Answer: One way would be to add mass to one side of the Rope Runner. Then the center of mass would be off to one side, in which case the Rope Runner would lean over. If it leans far enough, it will fall! Another way is to add a lot of mass to the Rope Runner somewhere above the height of the rope. That would raise the center of mass to a point above the rope, and again it would fall.

## What is Gravity?

Gravity is a force that pulls objects together. Everything in the universe has gravity: the stars) the sun and moon, our Earth., even you have gravity, Gravity is a “UNIVERSAL FORCE”.

In everyday life, what we mostly notice is the Earth’s gravity pulling on us. But, we too, are pulling the Earth. The Earth’s pull is much stronger than ours, though, because it has so much MASS. Objects with small mass do not pull very hard, which is why you don’t see pencils clinging to your fingers, or your breakfast stuck to your plate.

Gravity can reach over huge distances. The Earth and the sun are 93 million miles apart, but their combined gravitational force is strong enough to keep our planet from flying right out of the SOLAR SYSTEM. Even tiny Pluto, 3.6 billion miles from the sun. is held in its orbit because of the sun’s mighty gravitational field!

## Mass vs. Weight

Mass is the amount of MATTER in an object. The amount of matter depends on how many ATOMS there are. These atoms can be squeezed tightly together, in something dense, like a rock. Or they can have big spaces between the atoms, like in a piece of cotton. If you had pieces of rock and cotton that were the same size, the rock would have the greater mass.

The amount of gravitational force pulling any two objects together depends on the amount of their MASS—the greater their combined mass, the greater the attraction.

Weight is similar, but not quite the same thing as mass. Weight is a measure of the pull of gravity on an object. The pull we usually think of is that of the Earth, since that is where we usually are standing. But on planets with different mass, you would have a different weight. And in outer space, far from any major gravitational pull, you would weigh virtually nothing!

For further exploration visit:http://library.thinkquest.org/27585/

## Center of Mass 1

Sometimes the center of mass is not where you’d think, try making this gravity-defying Songbird.

## Instructions

Cut out the Songbird. You can color it if you like. Then take the paper clips and put one on the tip of each wing. Take a pencil, hold it upright, and balance the Songbird’s beak on the eraser!

## Center of Mass 2

What happens if the Center of Mass moves? Topsy-Turvy Trudy will give you an idea!

## Instructions

Cut out the 2 paper designs, Roll the tube with the face-side out, up to the line and tape, Tape one end shut, Drop the marble in, and tape the other end shut. Use the other paper as a stencil to trace Trudi onto the felt, Cut Trudi out, being very careful cutting the slits, Stop before the edge of the felt! Slide the tube into the slits as shown, Then roll Trudi down a ramp covered with fabric!

## Center of Mass 3

Another fun way to play with Center of Mass: THE VEGGE GUY GOES FISHING!

## Instructions

Insert the toothpicks into the radish for the legs. Make a bend 2 1/2 inches from one end of the wire, This makes a “fishing rod”. The remainder of the wire is the ”fishing line”. Insert the rod end into the center of the radish and you have a guy fishing.

Then slide 2-3 carrots on the end of his ” line”. The carrots are–you guessed it- fish! Stand him at the edge of a table, with his fishing line curling slightly under him. You can experiment with the angle of the “rod” and the number of “fish” necessary for the guy to balance.