Gravity and Orbits

Kepler’s 1st Law

Planets orbit the Sun in an ellipse, with the Sun at one focus

Kepler’s 2nd Law

Planets move faster when closer to the Sun and slower when farther away, sweeping equal areas in equal time

Kepler’s 3rd Law

Planets farther from the Sun take longer to complete an orbit

Ellipse

Oval-shaped path of an orbit

Focus (Foci)

Two fixed points in an ellipse; the Sun is at one

Eccentricity

How stretched an orbit is (0 = circle, closer to 1 = more stretched)

Perihelion

Point where a planet is closest to the Sun and moves fastest

Aphelion

Point where a planet is farthest from the Sun and moves slowest

Gravity

Force that pulls objects with mass toward each other

Mass

Amount of matter in an object; more mass = stronger gravity

Distance

Space between objects; more distance = weaker gravity

Newton’s Law of Gravity

Gravity increases with mass and decreases with distance

Orbital Period

Time it takes a planet to complete one full orbit

Astronomical Unit (AU)

Distance from Earth to the Sun

Kinetic Energy

Energy of motion; increases when speed increases

Gravitational Potential Energy

Energy from position; increases when an object is farther away from the Sun

Greater mass =

Stronger gravitational force

Closer two objects =

stronger gravitational attraction