Understanding friction in pushing, pulling, and rolling motion

Expert intro: This question checks how friction acts in different real-life situations and why its effect changes with motion and contact type.

Detailed walkthrough

What the question is testing

Friction is the force that opposes relative motion between surfaces in contact. It appears in many everyday actions, but its usefulness is not the same in every case.

Here, the task is to decide which of the three situations show the effectiveness of friction:

1. applying force on a wall
2. pulling an object
3. using a suitcase with wheels

Analyze each statement

i. Application of force on the wall

When you push on a wall, friction is involved at your feet and between your hand and the wall surface if there is contact. More importantly, a wall is a rigid object, so the force you apply does not produce motion, but friction still helps prevent slipping and allows you to apply force without losing balance.

So statement i can be considered correct in the context of friction’s role in resisting slipping and enabling force application.

ii. Pulling the object

When an object is pulled across a surface, friction is directly involved because it opposes the motion of the object. This is one of the clearest examples of friction at work.

So statement ii is correct.

iii. Suitcase with wheels

A suitcase with wheels moves with rolling friction rather than sliding friction. Rolling friction is much smaller, but it still exists and is important in allowing the suitcase to move smoothly while resisting unwanted motion.

So statement iii is also correct.

Correct option

Since all three statements describe situations where friction is effective, the correct answer is:

(D) i, ii and iii

Key point to remember

Friction is not only about stopping motion. It also helps with walking, gripping, pushing, and rolling. The type of friction may change, but the force is still present whenever surfaces interact.

Common confusion

A lot of students think friction only matters when something is sliding. That is not true. Static friction helps prevent slipping, sliding friction opposes movement during motion, and rolling friction acts when wheels are involved. Recognizing the type of friction is the key to solving this question correctly.

💡 Pitfall guide

A common mistake is to assume that a suitcase with wheels has no friction at all because it moves easily. In reality, wheels reduce friction, but they do not eliminate it. Another mistake is to think friction is only present when objects are sliding. Static friction is also important when you push against a wall or pull without immediate slipping. For exam questions like this, look carefully at whether the situation involves preventing slip, causing motion, or reducing resistance.

🔄 Real-world variant

If the suitcase were replaced by a suitcase without wheels, the situation would change from rolling friction to sliding friction, and the frictional force would be much larger. If the question instead asked, "Which cases involve sliding friction?" then pulling an object would clearly qualify, while the suitcase with wheels would usually involve rolling friction, not sliding friction. A wall push would mainly illustrate static friction rather than sliding friction.

🔍 Related terms

static friction, rolling friction, sliding friction