Answer & Explanation:
Friction is useful in the following situations:
The brakes on a bike: Friction is necessary in the brakes of a bike as it allows the brake pads to grip onto the rim or disc, which helps to slow down or stop the bike.
Inside the hub of the wheel on a bike: Friction is necessary to prevent the wheel from spinning too freely, which could lead to loss of control or accidents. The hub's bearings require just the right amount of friction to keep the wheel spinning freely but not too fast.
Friction is a nuisance in the following situation:
The moving parts of the chain and gears: Friction between the moving parts of the chain and gears can cause the bike to lose efficiency and require more effort from the rider. This can cause wear and tear on the bike and make it harder to ride.