In basic mechanics, ball bearings are used in cycles, scooters and other wheeled vehicles to achieve what effect between the wheel and the axle?

Introduction / Context:
Ball bearings are extremely common mechanical components that appear in bicycles, scooters, fans and many rotating machines. They are placed between moving parts in order to improve motion and reduce energy loss. This question tests your understanding of the basic purpose of ball bearings in everyday machines, especially the way they affect friction between a rotating wheel and its supporting axle.

Given Data / Assumptions:

• Ball bearings are placed between the wheel and the axle in cycles, scooters and similar vehicles.
• The question asks what effect they produce between the wheel and the axle.
• We consider normal operation, with properly lubricated bearings and no mechanical damage.

Concept / Approach:
Friction is the force that opposes relative motion between two surfaces in contact. In rotating machines, high friction at the axle wastes energy as heat and makes pedalling or driving harder. Ball bearings replace sliding friction by rolling friction. Small hardened steel balls roll between inner and outer races, separating the wheel hub from the axle. Rolling friction is much smaller than sliding friction, so the main purpose of a ball bearing is to reduce friction and allow smooth rotation with less effort and less wear.

Step-by-Step Solution:
Step 1: Identify the location of ball bearings in a cycle or scooter. They are placed between the rotating wheel hub and the fixed axle. Step 2: Recall that if metal surfaces slide directly on each other at the axle, friction and wear become large. Step 3: Understand that ball bearings introduce rolling elements between the surfaces, replacing sliding friction with rolling friction. Step 4: Rolling friction is much smaller than sliding friction, so the torque required to turn the wheel reduces significantly. Step 5: Conclude that the main effect is a reduction of friction between the wheel and the axle, leading to smoother motion and higher efficiency.

Verification / Alternative check:
Practical experience supports this idea. When bearings are worn out or badly lubricated, a bicycle wheel feels tight and hard to rotate, which means friction has increased. After servicing or replacing the bearings, the wheel spins freely with only a small push. Engineers design bearing systems explicitly to minimise friction and wear, not to increase them. Therefore it is clear that the correct role of ball bearings is to reduce friction between wheel and axle.

Why Other Options Are Wrong:
Increase the friction between the wheel and the axle is wrong because the aim is smooth rotation, not resistance.
Reduce the friction between the wheel and the ground is incorrect, since bearings are not placed at the wheel road contact region.
Increase both friction and wear at the axle is opposite to the purpose of using precision bearings.
Eliminate the need for lubrication at the axle is wrong because most bearings still require lubrication to work properly and to last long.

Common Pitfalls:
Students sometimes think that more friction is always good because it prevents slipping, but at the axle friction wastes energy. Another mistake is confusing tyre road friction, which should be adequate for grip, with axle friction, which should be as low as possible. Remember that ball bearings are used to reduce friction at the rotating joint, making motion smoother and more efficient.

Final Answer:
Ball bearings in cycles and scooters are used mainly to reduce the friction between the wheel and the axle.