Keep On Movin' There are many kinds of movement. Pulling, pushing, lifting, rolling, sliding, and dragging are just a few of the ways we move things. All movement is caused by force. A force is an action that starts or stops movement. One natural force called gravity, pulls everything towards the ground (learn more about gravity in our experiment!). Objects that are in motion want to stay in motion, and objects that are at rest like to stay at rest. This tendency to stay at rest or in motion is called inertia. The only way to stop inertia is by using a force. One way to move things is to slide them along another surface. Some surfaces make sliding easy, like sliding skis over snow, but some surfaces are hard to slide on, like trying to roller-skate over a cracked and bumpy sidewalk. The more bumpy or uneven a surface, the more movement is slowed down. This slowing force is known as friction. Wheels were one of the first mechanical inventions. They were invented over 6,000 years ago and make it much easier to move things -- like you! Gears are wheels with teeth. They work together to make things move more quickly or slowly. Different sized gears work together. For example, a large gear wheel turning once can make a smaller wheel turn many times. The smaller gear has to turn faster to keep up the bigger one (it's like a little kid walking with a grown up -- the kid has to take a lot of little steps to keep up with each grownup step). The smaller gear can be used to make something turn faster but with less power. A larger gear can be used to make something turn slower with more strength. Gears are used for movement in all kinds of machines like motors, eggbeaters, bicycles and watches. When an object spins around it creates a force called centrifugal force, which pulls it outward. Have you ever spun a bucket full of water around in circles? Centrifugal force is what keeps the water from spilling on you. Experiment with this concept!Checking out gravityEverything (even you!) is made up of a bunch of tiny particles called matter. Two objects that are the same size can have different amounts of matter. For instance, a tennis ball and a ball of lead can be the same size, but the ball of lead will weigh a lot more (you might have a hard time lifting it!). The ball of lead has a higher density of matter (there is a whole lot more matter stuffed into the lead ball than into the tennis ball). The more matter an object has, the more particles there are for gravity to pull to the ground. The greater the pull of the gravity, the heavier the object will be. The moon and the sun have gravity too (they're very serious!!!) but their pull on us isn't as strong as the Earth's pull (otherwise we'd all be sucked up into space!). The pull of the sun and moon do affect us here on Earth. For example, ocean tides are caused by the sun and moon's gravity pulling on the water. Because the moon is closer to earth than the sun, it pulls the oceans more than the sun. In the 1590's a scientist named Galileo came up with the idea that all objects are pulled towards the ground at the same speed, regardless of their weight. WANT SOME PROOF?MATERIALS:
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Which one landed first?How It Works:Both objects should land at the same time. Gravity pulls them down at the same speed despite the difference in their weight. If they were two differently shaped objects, this experiment wouldn't work. Forces other than gravity (air pressure, air currents) would affect the speed of their falls. What do you think?If you dropped a penny and a feather off the Empire State Building (or some other tall place) which would hit the ground first? |
