Physics · Class 11

Stick, slide and roll

Static friction matches the applied push up to a maximum μsN. It does not always equal that maximum. Above the threshold, a block starts sliding and resistance becomes μkN. Wheels have a smaller effective rolling resistance in this simplified trolley comparison.

Open the interactive experiment →

Friction adjusts before the block moves.

நிலை உராய்வு செலுத்திய விசைக்கு ஏற்ப அதிகபட்சம் வரை மாறும். அந்த வரம்பை மீறினால் பொருள் நழுவத் தொடங்கி இயக்க உராய்வு செயல்படும்.

Key notes, relationships and model limits

Key relationship

N = mg; sticking: f = F ≤ μsN. Sliding: f = μkN, a = (F − f)/m. Rolling resistance: fr = μrN.

Remember

Common trap

The simulator never accelerates a resting block below the static threshold.

Model limits

Constant positive push, horizontal surface, initially at rest. μk is capped at μs. Wheeled trolley uses an effective rolling-resistance threshold and negligible wheel inertia, not a full rolling-body model.

What you will learn

Identify sticking and sliding regimes; distinguish maximum static friction from actual friction; compare rolling resistance.

Try the experiment

Keep the block at rest, increase the push through the threshold, and compare with the wheeled trolley.

Think of it this way

A box remains still under a gentle push, then begins sliding after a stronger push.

Worked example

For m = 5 kg, μs = 0.5 gives 24.525 N maximum. A 20 N push sticks. A 30 N push slides; with μk = 0.3, a = (30 − 14.715)/5 = 3.057 m/s².

Why this matters

Choosing the contact regime before applying F = ma avoids impossible motion predictions.

Before you start

Vector components · velocity · SI units

Check your understanding

A resting block has a 25 N static limit and is pushed with 10 N. Its friction magnitude is…

25 N
10 N
Zero

Read the explanation

Static friction supplies the 10 N needed for equilibrium, below its maximum of 25 N.

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