A large gear with 30 teeth is turning a small gear with 10 teeth. How does the small gear behave?
AIt spins at the same speed with the same force
BIt spins 3 times faster but with less force
CIt spins 3 times slower but with more force
DIt does not move because the gears are different sizes
The gear ratio is 30:10, or 3:1. For every one turn of the large gear, the small gear turns 3 times — it spins faster. But the trade-off is that it has less rotational force (torque). This is like a bicycle in a high gear: fast spinning, less pushing power.
Question 2 True / False
Two meshing gears typically spin in the same direction.
TTrue
FFalse
Answer: False
When two gears mesh directly (their teeth interlock), they spin in opposite directions. If the left gear turns clockwise, the right gear turns counterclockwise. To make two gears spin the same direction, you need to add a third gear between them (an idler gear) or use a belt or chain.
Question 3 Short Answer
Why do bicycles have different-sized gears that riders can switch between?
Think about your answer, then reveal below.
Model answer: Different gear sizes let riders trade speed for power. A small gear driving a large wheel is hard to pedal but moves fast — good for flat roads. A large gear driving a small wheel is easy to pedal but moves slowly — good for climbing hills.
Bicycle gear shifting is one of the clearest everyday examples of the gear ratio trade-off. Low gear (easy pedaling, slow speed) uses a large front gear with a large rear gear to reduce the force needed. High gear (hard pedaling, high speed) uses combinations that make the rear wheel turn many times per pedal turn.