astr ch2-3

Astronomy Chapters 2-3 Study Sheet

Gravity and Orbits

Key Terms

geocentric theory

retrograde

prograde

epicycles

heliocentric theory

conjunction

opposition

Kepler’s 3 laws

semimajor axis

eccentricity

perihelion

aphelion

astronomical unit

Newton’s 3 laws

inertia

momentum

conservation of momentum

angular momentum

conservation of angular momentum

weight

surface gravity

orbital velocity

escape velocity

Other Concepts

How retrograde motion is explained in the geocentric and heliocentric theories

How do the phases of Venus show that it orbits the sun?

Applications of Newton’s 3 Laws

Mass is a measure of inertia

Identify action-reaction pairs of forces

Applications of conservation of momentum and conservation of angular momentum

Gravity acts between all masses

Work problems comparing gravity involving ratios

Why do objects in orbit seem “weightless”?

Why objects orbit instead of falling into the sun

What happens if an object in orbit speeds up or slows down?

Formulas (and the concepts behind them)



m

F

a

MM

a

P

aP







21

3

2

32

r

GM

v

r

GM

v

r

GMm

F

esc

orb

2

2







Essay and Short Answer Questions

 What were the significant contributions of Ptolemy, Copernicus, Tycho, Kepler,

Galileo, and Newton? Why were they significant?

 Why was the heliocentric theory considered such a bad thing? What problems

did people have with it?

 The development and proof of the heliocentric theory and the development of

the concept of gravity helped bring about the era of modern science. How did

it do this? What happened in this time period in science that was unique?

 Defend either the heliocentric or the geocentric theory. You may do this from

either the perspective of the 16 th century or the 21 st century. Although you may

use religious reasons, you must include scientific evidence as well.