Gravity

Mass or Weight?

Falling Objects

Orbits

Floating in SpaceTides

Floating on Water

What is gravity?

Credits

• Gravity is a force of attraction between two objects.

• All objects with mass have gravity. • Gravity acts like a magnet -

pulling objects together. • What causes gravity is not really

known.mass – the amount of matter in an object

What is gravity?

Mass or Weight?Mass is the "stuff" that matter is

made of. People often confuse mass with weight. But weight is actually the result of gravity pulling on the mass. We measure mass in grams. We measure weight in ounces and

pounds. Your mass stays the same if you could travel from planet to

planet, but your weight would vary depending on how the gravity of

that planet pulls on you.

Falling Objects• If a person drops a 10 pound ball and a 5

pound ball off a building at the same time, which one will hit the ground first?

• Will gravity pull harder on the 10 pound ball?

• This was the topic of a famous story about scientist Galileo Galilei who is said to have tried dropping two objects from the Leaning Tower of Pisa to find the answer to this question.

• You might be surprised to find out that the two objects hit the ground at almost the same time.

• Gravity works the same on all objects unless wind resistance gets in the way.

When one space object revolves around another, it is referred to as an

orbit. The earth orbits the sun. Our moon orbits the earth. Many of the

other planets in our solar system also have moons that orbit. Earth now has

many man-made objects orbiting. Satellites are placed in orbit around the

earth to assist with telephone calls, television, and other forms of

communication.

Orbits

So how do astronauts float in space if the pull of gravity is so strong? Astronauts don't actually float. They are being pulled by the Earth's gravity just the same as the rest of us. But they are also orbiting the Earth, or moving sideways. This is known as centrifugal force. This sideways movement actually is pulling them away from the Earth at the same time that the Earth is pulling them down, so it appears as if they are floating.

Floating in Space?

The Earth's tides are caused by the moon's gravitational pull on the oceans. Tides are the rise and fall of the ocean level as related to the shoreline which occurs over every 12 hours or so. To a lesser degree the moon also pulls on the rivers, lakes and land.

Tides

Floating on WaterWhen an object floats on the top of water, gravity is still in play. For an object to float, it must displace enough water to make up the same mass as the object itself. Once that happens, the remaining mass then sits on top of the water. For example: if a boat has a mass of 45 grams, it will displace 45 grams of water and if that has happened before the whole thing has sunk below the surface level of the water, the boat floats.

CreditsSource: http://idahoptv.org/dialogue4kids/season12/gravity/facts.cfm

Images:http://wikihelp.autodesk.com/Inventor/enu/2011/Help/Tutorials/125AutodeskInventorRou/4353Self-drainingLines/4360DefineGravity

http://lehighmicrogravity.com/

http://www.nationnews.com/articles/view/what-gravity/

http://www.scenicreflections.com/media/311485/GRAVITY_LESSONS_Wallpaper/