Answer:
We are five little objects of an everyday sort. You will find us all in a tennis court.
A shimmering field that reaches far. Yet it has no tracks, And is crossed without paths.
You can spin, wheel and twist. But this thing can turn without moving.
I can be short and sometimes hot. When displayed, I rarely impress.
I run through hills. I veer around mountains. I leap over rivers. And crawl through the forests. Step out your door to find me.
You use it between your head and your toes, the more it works the thinner it grows.