Finding the Center of Gravity

Finding the Center of Gravity

You will need: Card, pencil, compass, scissors, thread.

The story is told that while Sir Isaac Newton was in his garden an apple fell on his head from a tree. The great scientist immediately began to wonder what caused the apple to fall while the sun, moon and other stars remained overhead and (fortunately) showed no tendency to follow the apple.

The theory of gravity for which Newton is now famous proves valuable in many aspects of our modern life. Airplanes have to be so constructed and powered that they can successfully resist the force of gravity. Cars and trucks, and especially tall vehicles, have to be made with their centers of gravity low enough to withstand any tendency to topple over when driven around sharp corners.

Designers and engineers have to work out complicated mathematical formulae to discover the center of gravity of the product they are working on. Provided we use small objects, such as pieces of a card of different shapes, we can discover their centers of gravity.

For the first experiment draw a small circle with the aid of compass and pencil. Cut this disc out and note that it will balance perfectly when a needle point is placed on the center mark left by the compass.

Similarly, cut out a small square of card and draw diagonal lines from the corners of the square. The spot where the diagonals cross each other indicates the center of the square. When you place a needle point at this center you find that the square of card will balance perfectly.

The work of finding the center of gravity of an irregularly shaped piece of card becomes somewhat more complicated, however. First suspend the card from one of its corners by a piece of thread tacked to the wall. When it has settled in position take a ruler and continue the line of the thread straight down across the card. Next, suspend the card by another corner. Again, allow the card to become settled and use a ruler to extend the line of the thread across the card.

The center of gravity of the irregularly shaped piece of card occurs where these two diagonals cross each other. Place the card on a needle point at this spot and it will balance perfectly.