Mechanical reasoning tests ask how simple machines behave. A few rules answer most questions, with friction ignored:
- Gears that mesh turn in opposite directions. In a chain, gears in odd positions (1st, 3rd, 5th) turn the same way as the first.
- Speed follows teeth: driver speed × driver teeth = driven speed × driven teeth. A middle gear changes direction only, never the overall ratio.
- A straight belt keeps both wheels turning the same way; a crossed belt reverses one.
- A lever balances when weight × distance from the pivot is equal on both sides.
- A pulley system divides the load by the number of rope sections holding the moving block. Don't count the rope you pull on.
- A spring stretches in proportion to the force. Pressure is force ÷ area.
Draw arrows on gears, write weight × distance on levers, and count rope sections with your finger.