Gravitational Interactions & Cosmic Evolution Essential Facts
Stellar Distances • Light year • distance light travels in one year (about 6 trillion miles) • used to measure distances to stars and galaxies. • Astronomical unit • distance from the Earth to the Sun. • used to measure distances within the solar system.
Orbiting Objects • Falling toward the object they are orbiting but have enough speed to avoid hitting that object. • Earth is moving fast enough to fall continuously around the Sun. • The Moon is moving fast enough to fall continuously around the Earth. • Orbits are elliptical NOT perfect circles.
Newton’s Law of Universal Gravitation • Everything with mass pulls on everything else with mass with an attractive force. • The greater the masses of the two objects the greater the force. • (_____ proportional) • The greater the distance between the objects’ centers of mass the smaller the force. • (_____ proportional)
Newton’s Law of Universal Gravitation • UNIVERSAL: gravitational forces are calculated and work the same no matter where you are in the universe. • Any two objects that have MASS exert a gravitational force on one another. • 2 objects with mass = gravitational force
Earth’s gravitational field Object with mass EARTH
What causes ocean tides??? Fg = Gm1m2 r2 Force of gravity of Sun on Earth 3.55 x 1024 N Force of gravity of Moon on Earth 1.99 x 1020 N Sun’s force about 20,000 times Moon’s force
Sun Earth Moon NOT DRAWN TO SCALE! BUT… • The MOON has the greatest effect on tides. • It is DIFFERENCE in gravitational pull on the front side of Earth vs. the back side that causes tides. • The Sun’s effect on tides is minimal. Not a big difference in gravitational pull. A bigger difference in gravitational pull!!!
Cosmic Evolution • CHANGE OVER TIME – past, present, future of the universe • Hubble’s expanding universe – starting with Big Bang – most evidence supported model for the formation of the universe. • Models explain structure, scale and motion.
Stellar Evolution • CHANGE OVER TIME – past, present, future of a star • Sun is used to model how stars form, “live”, and “die out” • Our Sun will become a Red Giant then burn out and become a black dwarf. • Stars bigger than the Sun can become black holes when they burn out.