Question

A satellite moves in a circular orbit at constant speed$.$ Why doesn't its speed change even though it is acted on by a force$?$

Answer 1

Its speed does not change$,$ but its velocity $($speed and direction$)$ does$.$ Acceleration $($as in $F=ma$ $)$ implies a change of velocity but not necessarily of speed$.$ A circular orbit is the orbit which is exactly balanced so that the speed never changes$.$ There are billions of other$,$ elliptical$,$ orbits in which both speed and velocity change$.$ So you are asking why a circular orbit achieves that which is what defines a circular orbit$.$