Elliptical Orbit Pull

In the picture

1. 1The planet sits at one focus of the orbit.
2. 2The satellite moves along the ellipse.
3. 3The arrow shows the gravitational pull toward the planet.
4. 4The shaded wedge marks an area swept out in a time interval.

Examples

• The Moon orbiting Earth
• A comet looping around the Sun

Quiz: Elliptical Orbit Pull (Age 17)

1. 1

   Why does a satellite follow an elliptical path around a planet instead of flying in a straight line?

   • Gravity continuously pulls it toward the planet, changing its direction and speed.
   • No force acts on it, so it keeps the curved path it started with.
   • The planet’s rotation drags it around in a fixed ellipse.
2. 2

   Where is the planet located in a satellite’s elliptical orbit?

   • At the exact center of the ellipse.
   • At one focus of the ellipse.
   • At both foci of the ellipse at the same time.
3. 3

   According to Kepler’s equal-area law, how does a satellite’s speed change along an elliptical orbit?

   • It moves faster when it is nearer the planet and slower when it is farther away.
   • It moves faster when it is farther from the planet and slower when it is nearer.
   • It moves at the same speed everywhere along the orbit.

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.