# orbital motion

## orbital motion of the moon

Just as Earth orbits the sun, the moon also orbits Earth. The moon is affected by Earths gravity more than it is by the gravity of the sun because the moon is much closer to Earth. The gravity between Earth and the moon pulls the moon toward Earth. At the same time, the moon has forward velocity that partly counters the force of Earths gravity. So the moon orbits Earth instead of falling down to the surface of the planet. The Figure 1.2 shows the forces involved in the moons orbital motion around Earth. In the diagram, v represents the forward velocity of the moon, and a represents the acceleration due to gravity between Earth and the moon. The line encircling Earth shows the moons actual orbit, which results from the combination of v and a.

## what is orbital motion

Earth and many other bodiesincluding asteroids, comets, and the other planetsmove around the sun in curved paths called orbits. Generally, the orbits are elliptical, or oval, in shape. You can see the shape of Earths orbit in the Figure 1.1. Because of the suns relatively strong gravity, Earth and the other bodies constantly fall toward the sun, but they stay far enough away from the sun because of their forward velocity to fall around the sun instead of into it. As a result, they keep orbiting the sun and never crash to its surface. The motion of Earth and the other bodies around the sun is called orbital motion. Orbital motion occurs whenever an object is moving forward and at the same time is pulled by gravity toward another object.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

the shape of the path in question 2 is

a) round.

b) circular.

-->  c) elliptical.

d) none of the above

objects that have orbital motion include

a) moons.

b) satellites.

c) asteroids.

-->  d) all of the above

it takes earth 24 hours to complete each orbit.

a. true

-->  b. false

comets do not have orbital motion.

a. true

-->  b. false

an object with orbital motion is constantly accelerating.

-->  a. true

b. false

## diagram questions

No diagram questions associated with this lesson