Gravity

1. Gravity “It really sucks!”

2. Newton • Isaac Newton (1642-1722) was a British scientist who first explained how gravity works. • His ideas were inspired by seeing an apple fall from a tree. • Newton explained why gravity makes all things fall to the ground and planets orbit the sun.

3. Newton (page 2) • Newton realized that a planet’s orbit depends on its mass and its distance from the sun. • The further apart and the lighter two objects are, the weaker is the pull of gravity between them. • He figured out that you can calculate the pull of gravity between 2 objects by multiplying their mass by the square of the distance between them. • This calculation allows astronomers to predict precisely the movement of every planet, star, and galaxy in the Universe.

4. Newton (page 3) • Newton’s three laws of motion showed that every single movement in the Universe can be calculated mechanically. • Newton’s theory of gravity showed for the first time why the Moon stays in its orbit around the Earth, and how the gravitational pull between the Earth and the Moon can be worked out mathematically.

5. Gravity • is the attraction, or pulling force, between all matter. • It is what holds everything on Earth on the ground and stops it from flying off into space. • It is the same everywhere, it just depends on the mass of an object and distance between objects. • It holds Earth together, keeps the Moon orbiting the Earth, and all other celestial bodies orbiting the sun. (i.e.Planets; asteroids; comets)

6. Gravity (page 2) • The more mass an object has, and the closer it is to another object, the more strongly its gravity pulls. • Black holes have the strongest gravitational pull in the entire Universe. • The basic laws of gravity can be used for anything from detecting an invisible planet by studying the flickers in another star’s light, to helping the flight of a space probe.

7. Gravity (page 3) • Orbits are the result of a perfect balance between the force of gravity on an object (which pulls it inward towards whatever it is orbiting), and its forward momentum (which keeps it flying straight onward) • This momentum is called inertia. • Since these forces are “balanced” the planet stays fixed in an orbital path.

8. Black Holes • Places where gravity is so strong that it sucks everything in, including light. • They form when a star or galaxy is so dense that it collapses under the pull of its own gravity shrinking to a point so small which is called a singularity. • Around the singularity, gravity is so intense that space-time is bent into a funnel. • These may exist at the heart of every galaxy. • Matter spiraling into a black hole is torn apart and glows so brightly that it creates the brightest objects in the Universe – quasars.

9. Dark Matter • Space matter that we cannot see because it does not give off light. • Makes up about 90% of the matter in the Universe. • Astronomers know about it, because its gravity pulls on stars and galaxies, changing their orbits and the way they rotate. • The stars we see in the Milky Way are only a thin central slice, embedded in a big, bun-shaped ball of dark matter.

10. Dark Matter • Is of two kinds: the matter in galaxies (galactic), and the matter between them (intergalactic). • Galactic DM may be much the same as ordinary matter, but burned out early on in the life of the Universe. • Intergalactic DM is made up of W.I.M.P.s (Weakly Interacting Massive Particles) • The future of the Universe may depend on how much dark matter there is.