Day and night are caused by earth’s revolution on its axis.

FALSE

Explanation:

Day and night occurs due to the rotation of the earth around its internal imaginary axis. This occurrence of day and night divides the earth into two equal halves, where one of its side faces the sun and the other remains dark. This bright side, facing the sun experiences the day and the dark side experiences the night.

The main difference between rotation and revolution is that the rotation refers to an internal (inner) axis, around which a particular object moves. But on the other hand, revolution refers to the external (outer) axis, around which the object moves.

Hence, the above statement is FALSE.

they are known to reach a speed of 21 miles per hour