In order to reduce friction between surfaces in contact, it is generally more effective to change the type of motion from sliding to which other form of motion?

Introduction / Context:
Friction is a resisting force that acts between surfaces in contact. In many machines, vehicles and tools, it is desirable to reduce friction to save energy and prevent wear. One very common method of reducing friction is to replace sliding contact with rolling contact, as in the use of ball bearings and wheels. This question asks you to identify the correct change in type of motion that reduces friction effectively.

Given Data / Assumptions:

• Two surfaces are in contact and can experience either sliding or rolling motion relative to each other.
• We assume normal conditions where lubrication or special materials are not the main focus.
• The aim is to reduce frictional force between these surfaces.
• Several choices mention static, dynamic, sliding and rolling motion.

Concept / Approach:
Sliding friction occurs when one surface moves tangentially past another in direct contact, like a block dragged over a table. Rolling friction occurs when a body such as a wheel or ball rolls over a surface. In general, rolling friction is much smaller than sliding friction for the same normal reaction, because deformation and micro locking between surfaces are reduced. That is why vehicles use wheels, and machines use ball bearings. Therefore, changing from sliding motion to rolling motion significantly reduces friction in many practical systems.

Step-by-Step Solution:
Step 1: Recall that sliding friction involves surfaces scraping past each other, producing a relatively large resistive force.Step 2: Recall that rolling friction involves a rolling object, like a wheel, where only a small area is in contact at any instant.Step 3: Compare typical coefficients of sliding friction and rolling friction; rolling friction coefficients are much smaller.Step 4: Identify that using rollers or ball bearings converts sliding motion into rolling motion.Step 5: Note that static and dynamic terms refer to whether the body is at rest or moving and do not by themselves guarantee lower friction.Step 6: Conclude that friction is reduced by changing from sliding to rolling motion, which matches the correct option.

Verification / Alternative check:
Everyday examples confirm this reasoning. Moving a heavy cupboard directly on the floor is difficult, but placing it on rollers makes it much easier to push. Bicycles and cars use wheels to roll rather than slide, which greatly reduces energy loss and wear. Ball bearings are explicitly designed to replace sliding contact between parts with rolling contact. All these applications support the principle that rolling motion leads to smaller friction than sliding motion.

Why Other Options Are Wrong:
Changing from static to dynamic or from dynamic to static does not clearly address whether contact is sliding or rolling. Rolling to sliding would actually increase friction, which is the opposite of what we want. Therefore only the option that specifically replaces sliding with rolling matches the correct strategy for friction reduction.

Common Pitfalls:
Some learners may confuse the terms static friction and dynamic friction with sliding and rolling friction and may believe that any change from static to dynamic reduces friction. However, friction is strongly influenced by the type of contact. To avoid confusion, focus on the physical mechanism: rolling motion reduces direct scraping and interlocking of surface asperities, making it more efficient than sliding motion for most engineering applications.

Final Answer:
Friction is most effectively reduced by changing from sliding motion to rolling motion.