The Sumer Super Bike -- Page 32
This experiment is a quick demo involving nothing more than the front wheel of your bike, a broom, and some string, but it's a perfect way to demonstrate the principle of angular momentum. And you may just astound your friends while you're at it.
2 4-foot lengths of string
Bicycle wheel (the front wheel of a small bike works best)
2 friends of the same height
Take Care: Remember that as the wheel slows down, gravity will eventually overcome the angular momentum that kept it "afloat." Make sure you are able to control the wheel, so that it doesn't go rolling into something breakable. Also, make sure your fingers don't get too close to the spokes of the wheel, especially once it's spinning fast.
1. Tie the ends of one piece of the string together so you have a closed circle of string. Tie the other piece of string in the same way. You should have 2 loops of string.
2. Loop both pieces of string onto the broomstick.
3. Have both of your friends lift the broomstick onto their shoulders. Your friends should be facing each other.
4. Pick the wheel up and place it in between the 2 loops of string. Attach the strings to each side of the axle so that the wheel is suspended from the broomstick.
5. Start spinning the wheel as fast as you can. Remember, the wheel is being supported on its left and right sides by the string.
6. Ask your friends what will happen if you were to cut one of the strings holding the wheel. Common sense will lead them to answer that the wheel will fall.
7. While the wheel is spinning, cut one of the strings supporting it.
8. The wheel will not fall but will continue to spin in place. It will look as if it is hanging in the air, defying gravity.
Newton's Law of Friction -- Page 84
This experiment is a demonstration of one of the outside forces that acts on moving objects, causing them to slow down and stop: friction. We see it at work whenever we compare, for example, a hockey puck sliding across a skating rink with the same puck sliding across a carpeted floor. But this experiment shows how friction is at work between the pages of a book and how that force can build up astoundingly. Each overlap is a source of friction, but multiplying that force by 50, 60, or however many overlaps you managed to produce will increase the force a great deal.
2 paperback books of about the same size and number of pages
Take Care: No real problems here, just don't use someone's priceless first edition (even if it is in paperback).
1. You're aiming to "lock" the books together by having their pages overlap one another.
2. Put the books on a table, facing each other so that they just touch.
3. Lift each book up by the open-pages side so that the spines stay on the table but edge closer to each other by about 1 1/2 inches.
4. Rifle through the pages with your thumbs (from the back of the book to the front).
5. If you've managed to do this right, the pages of the books will overlap each other by the same 1 1/2 inches.
6. Try to pull the books apart. It seems as though they're locked together.
Theodore Maiman's Laser Oven -- Page 256
This experiment is a cool -- er, hot -- demonstration of the same principles at work behind a laser beam. Your handmade oven works by focusing the sun's rays toward the food tray. The foil increases the number of rays entering the oven. They can pass through the plastic, but the heat stays inside. The result: evidence you can eat.
A large pizza box (the sort you get when you order large takeout pizza)
8 1/2 inch X 11 inch sheet of sturdy clear plastic (preferable laminated)
Black construction paper
Take Care: Bare in mind that you have actually constructed an oven which can reach temperatures of up to 270 degrees Farhenheit. But it takes its time to reach that temperature. Leave half an hour for the oven to preheat and then you can figure on cooking things for twice as long as you would in a normal oven.
1. Draw a box on the top flap of the pizza box, about 1 to 2 inches from the edge.
2. Carefully cut along 3 of those 4 lines, leaving the line along the "hinge" of the box alone. Open and close several times to form a crease.
3. Cut a piece of foil the same size as this flap; glue it to the inside (lower) edge of the flap.
4. Measure and cut a piece of plastic just a bit larger than the opening. Tape this plastic to the underside of the box top, making sure it covers the cutout hole to form a complete air seal. At this point, the box top should have this new plastic seal on the underside: the foil-backed flap opens up from this plastic layer.
5. Cut a second piece of foil and glue it to the bottom (inside) of the pizza box.
6. Cut some of the black construction paper to fit this same base; tape it on top of the foil on the base. The now-covered foil will work as a heat insulator rather than as a reflector.
7. Aim the box so that it opens toward the Sun.
8. Prop the flap open -- but with the box top shut -- to get the oven working.
9. You can cook all sorts of thing -- English muffins, s'mores, and maybe even more pizza -- provided they don't protrude higher than the box top.