Objective
Describe the forces that keep objects in orbit in the Solar System.
Gravity Reading
(source: Idaho Public Television – Dialogue for Kids)
Gravity is a force of attraction between two objects. All objects withmasshave gravity. Gravity acts like a magnet - pulling objects together. What causes gravity is not really known.
The Earth has gravity. Gravity holds everything close to this planet. Trees, water, animals, buildings, and the air we breathe are all held here by gravity. Everything in the universe has gravity. Even our own bodies have gravity. The Earth's gravity is far stronger than our own so we don't notice our bodies’ gravity.
Gravity is affected by the size andhow close the objects are. The Earth and the Moon have a stronger pull on each other than the Earth and say... Jupiter because the Earth and Moon are closer to one another. Earth has a stronger pull than the Moon because it is larger. There is more pull on our bodies here on the Earth than astronauts who have gone to the Moon would have while they are visiting there. We don't actually "feel" gravity. We only feel the effects of trying to overcome it by jumping or when we fall.
Orbits
When one space object revolves around another, it is referred to as an orbit. The Earth orbits the Sun. Our Moon orbits the Earth. There are manymoons that orbitother planets. There are many man-made objects orbiting Earth. Satellites are in orbit to assist with telephone calls, television, and other forms of communication.Astronauts have sometimes left junk orbiting Earth, too. Gloves, tools, and other junk continuously orbit our Earth.
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? Galileo Galileiis 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 the same time. Gravity works the same on all objects unlesswind resistancegets in the way. So, if one of those balls had been attached to a parachute, it would have slowed the ball down. Amazing science!
Black Holes
How strong can gravity get? Imagine gravity pulling on everything and not letting it escape - not even light! That is what makes a black hole. The gravity in a black hole pulls everything back in toward its center which may be as small as a singleatom. This makes a black hole invisible because even light is unable to break away from its effects. Scientists believe there may be millions of black holes in theMilky Way Galaxy.
Floating in Space?
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 ascentrifugalforce. 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.
Isaac Newton
Sir Isaac Newton (1642- 1727) was a scientist who is credited
with discovering gravity. You would think that gravity would be a well-known concept since all of us have been aware of
it since we were little kids dropping our spoons on the floor from our high chair just to make mom come and get
it. But it wasn't until Newton published his ideas in a book
in 1687 that the scientific world had gravity as a defined
term. Newton is well known for his Three Laws of Motion
which explain how the physical laws direct the motion of objects.