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Physics · Class 11

Dry or lubricated

Laws of Motion

A lubricant can reduce direct contact between rough surfaces and change their friction. Here you choose lower coefficients and compare identical blocks. A weaker push may move the lubricated block while the dry block remains stuck. Real lubricants also produce viscous resistance; that additional behavior is outside this model.

Open the interactive experiment →

Reduce contact resistance and compare the result.

மசகு பொருள் மேற்பரப்புகளின் நேரடி தொடர்பையும் உராய்வையும் குறைக்கலாம். ஒரே விசையில் மசகிடப்பட்ட பொருள் நகர்ந்தாலும் உலர்ந்த பொருள் நிலையாக இருக்கலாம்.

Key notes, relationships and model limits

Key relationship

For this comparison μs = 1.25μk. Once sliding, a = (F − μkmg)/m; below μsmg the block remains at rest.

Remember

A lubricant can reduce direct contact between rough surfaces and change their friction. Here you choose lower coefficients and compare identical blocks. A weaker push may move the lubricated block while the dry block remains stuck. Real lubricants also produce viscous resistance; that additional behavior is outside this model.

Common trap

Lubrication does not imply zero friction, and a particular coefficient ratio is not universal.

Model limits

Illustrative Coulomb-friction coefficients, equal constant pushes, no viscosity or lubricant heating. The lubricated coefficient is capped at the dry coefficient; μs/μk = 1.25 is a chosen example, not a universal law.

What you will learn

Compare friction thresholds and motion with changed contact coefficients.

Try the experiment

Try the only-lubricated-block preset, then increase the push so both move. Set coefficients equal to recover identical motion.

Think of it this way

Oil in a hinge changes the resistance felt when opening the same door.

Worked example

A 5 kg block pushed by 35 N has a = 3.076 m/s² for μk = 0.4 and a = 6.019 m/s² for μk = 0.1.

Why this matters

Comparing controlled loads isolates the surface effect from changes in mass or driving force.

Before you start

Vector components · velocity · SI units

Check your understanding

In this model, reducing μk while both blocks slide at the same applied force makes acceleration…

Read the explanation

The resisting force μkmg becomes smaller, so the net force and acceleration increase.

Course connection: CBSE XI Chapter 4; NEET/Main Unit 3; JEE Advanced Mechanics. Apply each exam’s stated assumptions.