For Parents: Interesting Facts for Kids

Gravity Gravity is a pulling force between one object and another. The more the matter, the bigger the pull. Some collapsed stars have very strong gravitational pulls. Their pull is so strong that nothing can escape them, not even light. Scientists call these stars black holes. Anything that gets too near black hole will be sucked in.
Force Force means anything that pushes and pulls. Everything around you is pushing or pulling, and being pushed and pulled. Whenever you push on something, it pushes back. When you increase the distance of movement you use less force. This is Newton's Third Law of Motion.
Friction Friction happens when two surfaces come in contact with each other. Without frictional book would slip out of your hands no matter how tightly you tried to hold it. Food would slip off your fork which you would not have been able to hold in the first place. You know that people used to rub two sticks together to start fires. The fire starts because of the heat caused by the friction.

The inclined plane is a kind of simple machine with slanted surface. On mountains or steep hills, roads, and walking trails don't go straight up the mountain. It would be too difficult to walk or drive that way. Instead, the road winds back and forth up the mountain. These inclined planes are called switch backs, which are easier to climb.
             The pyramids in Egypt are made of huge stone blocks. For years people have been wondering how they moved all those heavy blocks around. The best guess is the Egyptians pushed the blocks up inclined planes in order to build the pyramids.

The lever is simple machine made up of a stiff arm or arms that pivots or turns. The point that a lever turns on is called the fulcrum. The load is the force of the thing you are trying to move. Over 2000 years ago, a Greek scientist named Archimedes (ark a MEE dees) figured out how and why levers worked. People had been using levers for a long time, but he was the first to explain them using math. Legend credits Archimedes with saying, "With a big enough lever, you can move the world."

The pulley is a simple machine made of a rope or chain wrapped around the wheel. A movable pulley reduces the amount of force needed to lift an object by object by increasing the distance over which the force is applied. The useful pulley is one of the earliest and simplest wheel devices. Back in the eighth century B.C., the country that is now Syria may have discovered that a small wheel within a frame made it easier to pull up a heavy weight hanging from a rope running over the wheel. Engineers in ancient times used this knowledge to their advantage in the construction of many monuments and temples.

The wheel and axle is a simple machine made of a large wheel attached to a post or axle. Spanish speaking people arrived in California with their own mining technology. The arrastre worked much like a wheel and axle. An upright post was turned by a mule walking on a circular path. The post, twirling a granite block, ground up rocks that contained gold.

The wedge is two inclined planes joined back to back. Wood has been the main medium for crafts and construction among the Alaskan Natives and American Indians of Northwest Coast region. When building their wooden plank houses, one of the their main tools was the wedge. Hardwood wedge enable workers to split long planks from tree trunks. Other wooden products of the American Indians include totem poles, canoes, masks, containers, figurines, tools, and weapons.

The screw is an inclined plane wrapped around a post. One of the first screw machines was invented by Archimedes in the third century B.C. Archimedes, perhaps the greatest mathematician of his time, designed a machine to lift fresh water from the hold of a ship belonging to King Hiero II of Syracuse. Archimedes' machine had a watertight cylinder enclosing a spiral running from end to end (something like the inside of a mincer), with its lower end immersed in the water. As the machine was turned by hand, the water collected in the rotating spiral blades and was lifted out of the ship's hold.