How many Let's Find Out About Simple Machines books are there?

There are 2 books in the Let's Find Out About Simple Machines series by Martha Elizabeth Hillman Rustad, for ages 5-8.

Let's Find Out About Simple Machines Books in Order — Wonder

Let's Find Out About Simple Machines is a 2-book series for ages 5–8 by Martha Elizabeth Hillman Rustad. Each book stands alone — start anywhere.

Start anywhere — each book stands alone.

That said, Inclined Planes and Wheels and Axles are great first picks.

No particular order needed — browse and pick what catches your eye.