Slow simulations on mobiles

Hi

I've created several interactive animations (simulations) that use movieclips moved or rotated by code according to parameters entered during run-time. However, even though these animations run smoothly on computers, they run very slowly on mobiles.

Then I used tweens instead of moving the object by code, and it worked smoothly on mobile devices.

What is the reason and how to solve this?

Thank you in advance