World 4 · Compound Machines · 9 min · PROThe Grand Machine
Gear, lever and pulley together
PRO · Simple Machines
World 4: Compound Machines is part of PRO
The first world of Simple Machines is free. PRO opens the other 32 lessons in 6 worlds — simulations, quizzes and all.
PRO includes
- All 26 labs — every world, every lesson
- Practice exams and certificates
$8.33/mo, billed yearly ($99.99) · or $39.99 monthly