Revolution and orbit

The idea

Revolution is the motion of an object around another object, different from rotation; the path an object takes while revolving around another is its orbit.

Round the tree

A child runs round a tree. Another child spins on the spot.

Are these two motions the same?

• Yes, they are the same
• No, they are different
• We cannot tell

Rotate, revolve, or both

Try each motion. The orange pin shows the turning. The dotted path is the orbit.

Two different motions

Spinning on its own axis is rotation. Moving around another object is revolution, and its path is the orbit.

Revolution is the motion of an object around another object, different from rotation; the path an object takes while revolving around another is its orbit.

Notes

Revolution is the motion of an object around another object, different from rotation; the path an object takes while revolving around another is its orbit.

Check yourself

Revolution is the motion of an object …

The path an object takes while revolving around another is its …

A child runs round a tree. The child’s motion round the tree is like …

Which of these is rotation and not revolution?

• on its own axis. Turning on its own axis is rotation, not revolution.
• around another object — correct. Yes! The Earth goes around the Sun.
• in a straight line. A straight line is not a revolution. Revolving means going round another object.
• axis. The axis is the line an object turns around when it rotates.
• shadow. A shadow is made when light is blocked. The path of a revolving object is its orbit.
• orbit — correct. Yes! The dotted path is the orbit.
• revolution — correct. Yes! The child goes round another object.
• a spinning top. A spinning top turns on the spot, which is rotation. The child goes round another object.
• rotation. Rotation is turning on a line through the object itself. The child goes round another object.
• The Moon going round the Earth. Going round the Earth is revolution.
• The Earth spinning on its axis — correct. Yes! It turns on its own axis.
• The Earth going round the Sun. Going round the Sun is revolution.