- Slides: 17
The gravity of gravity.
What is gravity One of the fundamental forces of the universe, one that causes every object in the universe to attract every other object. Anything that has a mass, anything that contains physical matter, will be attracted to every other object with mass.
How does distance affect gravity? If you double the distance between two objects, you cut the force of gravity between them to a quarter. That’s why you don't feel a strong force of gravity between you and the planet Mars is small and so far away.
The Effect of Gravity causes the motions of planets, stars, and galaxies. It's why the Moon orbits around the Earth, and the Earth orbits around the Sun, and the solar system orbits around the galaxy. It's all because of gravity.
Why are planets and stars round? Gravity is the reason they're spherical. In the early solar system, it was very. . . messy. There were millions of bits of rock flying all over the place. In the early mess of the solar system, the objects tended to be gravitationally attracted to each other.
What happened to the mess? Things combined more than they broke apart. The heaviest elements like iron had the strongest forces of gravity, so they attracted together quickly, forming what would become the core of planets like the Earth. Then lighter layers formed on top as objects gradually got bigger through all the collisions.
What’s a radial force? Think of a circle. The longer the radius, the weaker the force. As planets gradually grew in size, they tended to do it in a really even way. As the matter was pulled in, the rotation only increased, just like how spinning ice skaters will spin faster when they move their arms closer to their body. This rotation helped smooth out the surface. It was for these reasons that the planets over time became more and more spherical.
Gravity and the Tides What is a tide and what causes them? the alternating rise and fall in sea level produced by the gravitational attraction of the moon and the sun. Tides are created because the Earth and the moon are attracted to each other. The moon tries to pull at anything on the Earth to bring it closer. Since the water is always moving, the Earth cannot hold onto it, and the moon is able to pull at it.
High and Low Tides Each day, there are two high tides and two low tides. There is about 12 hours and 25 minutes between the two high tides. The gravitational attraction of the moon causes the oceans to bulge out in the direction of the moon. The combined gravitational forces of the Earth, moon and sun cause the world's oceans to rise and fall.
Spring Tides When the moon is full or new, the gravitational pull of the moon and sun are combined. At these times, the high tides are very high and the low tides are very low. Spring tides are especially strong tides (they do not have anything to do with the season Spring). They occur when the Earth, the Sun, and the Moon are in a line. Spring tides occur during the full moon and the new moon.
Neap Tides During the moon's quarter phases the sun and moon work at right angles, causing the bulges to cancel each other. Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons.