You may have played on a see-saw in parks or gardens. But how does the centre of gravity affect a balance? This is what we are going to find out.
Things Required:
Straight pin
Small index card
Straw
Scissors
2 wooden blocks of equal height and not as wide as the length of the straw
Ruler
Marking pen
Directions:
Use the ruler to find the centre of the straw and mark the spot with the marking pen. Cut a 1-inch (2.5 cm) slit in each end of the straw, as shown in the diagram. The slits should be in the same relative position on each end. Divide the index card in half by folding and cutting along the fold. Insert the paper pieces in the slits on each end of the straw to form two flat surfaces that are parallel with each other. These papers will act as weighing pans.
Punch the straight pin through the centre of the straw, leaving an equal amount of the pin sticking out on each side of the straw. Position the two wooden blocks on a table and place the ends of the pin on the edges of the blocks. Move the paper pieces outward to increase the downward pressure on the weighing pan and inward to decrease the pressure. Position the paper weighing pans to make the straw level with the table.
This Is What Happens:
Moving the paper weighing pans in and out causes the straw to rotate around the pin. A position was found to make the straw level with the table.
Science Behind It:
The position of the paper weighing pans affects the balance of the straw. The farther the paper is moved away from the pin, the more downward is the rotation of the straw on that side. The children of different weights experience the same thing when sitting on a see-saw. They move away from the centre of the board to increase their downward rotation and closer to the centre to decrease it. The straw is balanced when the position of the paper places the centre of gravity of the balance at the place where the pin is inserted. The center of gravity is the point where an object balances. The downward rotation on both sides of the centre of gravity point is always the same.
