Orbits & Gravitational Attraction

What is an orbit?

The path followed by an object moving around another object under gravity.

What force keeps a planet in orbit around a star?

Gravitational attraction.

What force keeps an artificial satellite in orbit around Earth?

Gravitational attraction.

What force keeps the Moon in orbit around Earth?

Gravitational attraction.

Why does an orbiting object not simply travel in a straight line?

Gravity provides a resultant force that continually changes its direction.

What is circular motion?

Motion along a circular path.

Can an object travelling at constant speed in a circle be accelerating?

Yes, because its direction and therefore its velocity continually change.

Why is velocity changing during circular motion?

Velocity is a vector, so a change in direction is a change in velocity.

In which direction does the resultant force act during circular motion?

Towards the centre of the circular path.

What provides the centripetal force for an orbiting satellite?

Gravity.

What does centripetal mean?

Directed towards the centre of a circular path.

Why does a satellite not fall straight down to Earth?

It has sideways velocity, so it continually falls around Earth rather than directly towards its surface.

What happens to an orbiting object if there is no resultant force?

It continues in a straight line at constant velocity.

What is a natural satellite?

An object that naturally orbits a larger body.

What is an artificial satellite?

A human-made object placed into orbit.

What is the difference between a planet's orbit and its rotation?

Orbit describes movement around another object, while rotation describes spinning about its own axis.

What is an elliptical orbit?

An orbit shaped like an ellipse rather than a perfect circle.

Are all planetary orbits perfectly circular?

No, planetary orbits are generally elliptical.

Why does gravitational attraction affect both objects in an orbital system?

Both objects exert equal and opposite gravitational forces on each other.

What is the relationship between gravity and the motion of planets?

Gravity provides the resultant force needed to keep planets in orbit.