The substances that are applied between moving surfaces to reduce friction and allow smoother motion are called what?

Introduction / Context:

This question addresses the concept of friction and the materials used to control it in machines and everyday devices. Friction between surfaces can cause wear, heating, and energy loss. Engineers and technicians use certain substances to reduce friction, making movement smoother and extending the life of components. Knowing the correct term for these substances is an important part of basic mechanics.

Given Data / Assumptions:

• Two solid surfaces move or slide relative to each other.
• Contact between them produces friction that opposes motion.
• A substance can be applied between the surfaces to reduce this friction.
• We are asked what such friction reducing substances are called.

Concept / Approach:

Lubricants are substances, often oils, greases or special fluids, that are placed between moving surfaces to reduce direct contact between solid asperities and therefore decrease friction and wear. The lubricant creates a thin film or layer which allows surfaces to slide more easily. Irregularities are microscopic bumps on surfaces that actually cause friction, adhesives increase sticking, and viscosity describes the internal resistance to flow of fluids, not the friction between solid surfaces directly. Thus, the correct term for friction reducing substances is lubricants.

Step-by-Step Solution:

Verification / Alternative check:

Everyday examples support this. Engines require engine oil, cycle chains use lubricating oil, and door hinges may be oiled or greased to stop squeaking and make movement easier. In each case, the substance is known as a lubricant. Textbooks on friction explicitly state that lubrication is a standard method to reduce friction, and the materials used are called lubricants. No reference calls them irregularities or adhesives in this context.

Why Other Options Are Wrong:

• Irregularities: These are microscopic bumps on surfaces that cause friction, not substances that reduce it.
• Adhesives: Materials like glue or tape increase bonding or sticking between surfaces, increasing resistance to motion.
• Viscous substances: Viscosity refers to internal resistance to flow in fluids. Some lubricants are viscous, but the general term for friction reducing substances is lubricants, not viscous.

Common Pitfalls:

Students sometimes associate viscous liquids with lubrication and incorrectly think viscosity is the main label. While some lubricants are viscous oils, the defining feature is their role in reducing friction, not just their thickness. Another error is to overlook that irregularities and adhesives play opposite roles, increasing friction instead of reducing it. Always focus on the function: if the substance is used specifically to reduce friction between moving parts, it is a lubricant.

Final Answer:

The substances used to reduce friction between moving surfaces are called lubricants.