Rolling Friction Question Bank – CBSE 11 & NEET Foundation
Rolling Friction – Easy NEET Notes
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1. Rolling Without Slipping
- When a ring, wheel, or sphere rolls on a horizontal surface without slipping, ideally there should be no frictional force.
- At any instant, only one point of the body touches the ground.
- This contact point is momentarily at rest with respect to the ground.
- Since there is no relative motion at the contact point, kinetic friction does not act.
- In the ideal case, static friction is also zero.
- Therefore, the body should continue moving with constant velocity according to Newton's First Law.
NEET Point
Pure rolling without slipping on an ideal surface requires no friction force.
2. Why Does a Rolling Body Stop in Real Life?
- In practical situations, a rolling wheel or ball eventually slows down and stops.
- This shows that some resistance to motion is acting.
- This resistance is called rolling friction or rolling resistance.
- To keep the object rolling at constant speed, an external force must be applied.
Definition
Rolling friction is the force that opposes the motion of a rolling body.
3. Magnitude of Rolling Friction
- Rolling friction is much smaller than static friction.
- Rolling friction is also much smaller than sliding (kinetic) friction.
- It may be 100 to 1000 times smaller (2–3 orders of magnitude).
Relation
F_{\text{rolling}} < F_{\text{sliding}} < F_{\text{static(max)}}
NEET Point
Rolling friction is the least among common types of friction.
4. Importance of the Wheel
- Because rolling friction is very small, moving objects on wheels requires much less force.
- This is why the invention of the wheel became one of the greatest achievements in human history.
- Vehicles, carts, and machines can move efficiently because of low rolling friction.
5. Cause of Rolling Friction
- Rolling friction arises due to the deformation of surfaces in contact.
- When a wheel rolls, both the wheel and the surface become slightly compressed.
- Therefore, contact is not at a single point but over a small finite area.
- Because of this deformation, the contact force becomes slightly tilted.
- The horizontal component of this contact force opposes the motion.
- This opposing force is called rolling friction.
NEET Point
Rolling friction mainly occurs due to deformation of the wheel and the surface.
6. Why Friction Is Often Undesirable
- Friction opposes relative motion.
- It converts useful mechanical energy into heat energy.
- This leads to power loss in machines.
- Continuous friction also causes wear and tear of machine parts.
Effects of Friction
- Energy loss
- Heating
- Reduced efficiency
- Damage to surfaces
7. Methods to Reduce Friction
(a) Lubrication
- Lubricants such as oil and grease are used between moving surfaces.
- They reduce direct contact between surfaces.
- Hence, friction decreases.
(b) Ball Bearings
- Ball bearings are placed between moving machine parts.
- They convert sliding friction into rolling friction.
- Since rolling friction is much smaller, power loss decreases.
NEET Point
Ball bearings reduce friction by replacing sliding motion with rolling motion.
(c) Air Cushion
- A thin layer of air can be maintained between moving surfaces.
- The surfaces then do not touch each other directly.
- Friction becomes very small.
Example
- Air hockey table
- Air-cushion transport systems
8. Useful Effects of Friction
Although friction causes energy loss, it is extremely important in daily life.
(a) Walking
- While walking, the foot pushes the ground backward.
- Static friction from the ground pushes us forward.
- Without friction, walking is impossible.
(b) Brakes
- Brakes use friction to stop vehicles.
- Friction converts kinetic energy into heat.
- Thus, the vehicle slows down and stops.
(c) Motion of Cars
- A car moves because of friction between tyres and the road.
- The tyres push the road backward.
- The road exerts a forward frictional force on the tyres.
- This forward friction accelerates the car.
Example
On an icy road, friction is very small, so vehicles may skid and cannot accelerate properly.
Quick NEET Revision
Rolling Friction
- Opposes rolling motion.
- Smallest type of friction.
- Caused by deformation of surfaces.
- Much smaller than sliding friction.
Order of Friction
F_{\text{rolling}} < F_{\text{sliding}} < F_{\text{static(max)}}
Applications
- Wheels
- Ball bearings
- Vehicles
- Machinery
Important Facts
- Pure rolling on an ideal surface → friction ≈ 0.
- Real surfaces deform → rolling friction appears.
- Ball bearings reduce friction by converting sliding into rolling.
- Walking, braking, and vehicle motion require friction.
NEET One-Liner
Rolling friction is a small resistive force produced due to deformation of the rolling body and the surface in contact, and it is much smaller than sliding or static friction.
ROLLING FRICTION
- Definition
- Friction opposing rolling motion
- Also called rolling resistance
- Acts opposite to motion
- Ideal Rolling (Without Slipping)
- One point touches the ground
- Contact point is at rest relative to ground
- No kinetic friction
- No static friction required
- Body moves with constant velocity
- Real Situation
- Rolling body slows down
- Resistance acts on motion
- Called rolling friction
- External force needed to maintain motion
- Cause of Rolling Friction
- Deformation of wheel
- Deformation of surface
- Contact area becomes finite
- Contact force develops a component opposing motion
- Magnitude
- Very small compared to other frictions
- Less than sliding friction
- Less than static friction
- 100–1000 times smaller
- Order of Friction
- Rolling Friction < Sliding Friction < Static Friction (Maximum)
- Importance of Wheel
- Reduces friction greatly
- Makes transportation easier
- Major milestone in human history
- Disadvantages of Friction
- Opposes motion
- Produces heat
- Causes energy loss
- Reduces efficiency
- Causes wear and tear
- Methods to Reduce Friction
- Lubrication
- Oil
- Grease
- Ball Bearings
- Convert sliding friction into rolling friction
- Reduce power loss
- Air Cushion
- Thin layer of air between surfaces
- Very small friction
- Lubrication
- Useful Applications of Friction
- Walking
- Static friction helps us move forward
- Brakes
- Friction stops vehicles
- Cars
- Tyres push road backward
- Road friction pushes car forward
- Walking
- NEET Key Points
- Rolling friction is the smallest type of friction
- Caused by deformation of surfaces
- Ball bearings reduce friction
- Pure rolling ideally requires no friction
- Walking and vehicle motion require friction
CBSE Class 11 Physics Question Bank
Topic: Rolling Friction (School Exams, Unit Tests & NEET Foundation)
1. Multiple Choice Questions (MCQs)
Q1. Rolling friction is also called:
Q2. Rolling friction is generally:
Q3. The main cause of rolling friction is:
Q4. Ball bearings reduce friction by converting:
Q5. In ideal pure rolling without slipping:
Q6. Which friction is the smallest?
2. Very Short Answer Questions (1 Mark)
Q1. What is rolling friction?
Q2. What is another name for rolling friction?
Q3. Which is smaller: rolling friction or sliding friction?
Q4. Why are wheels used in vehicles?
Q5. Name one device that reduces friction in machines.
3. Short Answer Questions (2–3 Marks)
Q1. Why is rolling friction less than sliding friction?
• In rolling motion, there is very little relative motion between surfaces.
• Only slight deformation occurs at the contact area.
• Therefore, rolling friction is much smaller than sliding friction.
Q2. What causes rolling friction?
• During rolling, the wheel and surface deform slightly.
• The contact area becomes finite instead of a point.
• This produces a force component opposing motion.
• This opposing force is called rolling friction.
Q3. How do ball bearings reduce friction?
• Ball bearings are placed between moving parts.
• They replace sliding friction with rolling friction.
• Since rolling friction is smaller, energy loss decreases.
Q4. State two disadvantages of friction.
1. Causes wear and tear of machine parts.
2. Produces heat and energy loss.
4. Long Answer Questions (4–5 Marks)
Q1. Explain rolling friction and its causes.
Causes:
• The rolling body and surface deform slightly.
• Contact occurs over a finite area instead of a point.
• The contact force develops a component opposite to motion.
• This component opposes rolling and produces rolling friction.
Rolling friction is much smaller than static and sliding friction and helps vehicles move efficiently.
Q2. Explain the importance of friction in daily life.
• Walking is possible due to static friction.
• Vehicles move because friction acts between tyres and roads.
• Brakes use friction to stop vehicles.
• Writing on paper is possible due to friction.
• Holding objects firmly requires friction.
Thus, friction is essential despite causing energy losses.
5. Fill in the Blanks
1. Rolling friction is also called __________.
2. Rolling friction is __________ than sliding friction.
3. Ball bearings reduce __________ friction.
4. Friction converts mechanical energy into __________ energy.
5. Walking is possible due to __________ friction.
6. The invention of the __________ reduced friction in transportation.
6. Assertion and Reason Questions
Q1.
Assertion (A): Rolling friction is smaller than sliding friction.
Reason (R): Rolling surfaces undergo less relative motion than sliding surfaces.
Q2.
Assertion (A): Ball bearings are used in machines.
Reason (R): They increase sliding friction.
Q3.
Assertion (A): Friction is always harmful.
Reason (R): Friction causes wear and tear.
7. Statement-Based Questions
Q1.
Statement I: Rolling friction is the smallest type of friction.
Statement II: Rolling friction is caused mainly by surface deformation.
Choose the correct option:
Q2.
Statement I: Walking is possible without friction.
Statement II: Static friction helps us walk.
8. Match the Columns
| Column A | Column B |
|---|---|
| A. Ball Bearing | 1. Walking |
| B. Static Friction | 2. Rolling Friction |
| C. Wheel | 3. Reduces Friction |
| D. Rolling Motion | 4. Easier Transportation |
9. Case Study-Based Questions
A bicycle moves smoothly on a road because its wheels roll over the surface. The rolling friction between the tyres and road is very small compared to sliding friction. Ball bearings are used in the wheel assembly to reduce friction further.
Q1. What type of friction acts on the bicycle wheels?
Q2. Why is rolling friction preferred over sliding friction?
Q3. What is the function of ball bearings?
Q4. What is the main cause of rolling friction?
10. Competency-Based Questions
Q1. A heavy box requires 300 N force to slide but only 20 N force when placed on rollers.
(a) Which friction is acting in the second case?
Answer: Rolling friction.
(b) Why is the required force smaller?
Answer: Rolling friction is much smaller than sliding friction.
Q2. Why do suitcases have wheels attached to them?
Important CBSE Exam One-Liners
- Rolling friction is the smallest type of friction.
- Rolling friction is caused by deformation of surfaces.
- Ball bearings reduce friction by converting sliding into rolling.
- Walking requires static friction.
- Friction is both useful and harmful.
- Wheels reduce friction and make transportation easier.
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