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Do You Know
Q1. Friction always acts in the direction?
Answer: Opposite to motion
Detailed Explanation:
Friction is a contact force that acts between two surfaces when they touch each other. Its main function is to oppose motion or the tendency of motion.
Whenever an object moves or tries to move, friction acts in the opposite direction to slow it down or stop it.
Why opposite direction?
If friction acted in the same direction as motion, it would increase speed. But in reality, it always resists movement.
Examples:
- Applying brakes on a bicycle slows it down due to friction
- Rubbing a matchstick produces heat because of friction
Exam Line:
“Friction always acts in the direction opposite to motion and resists movement.”
Q2. Which type of friction is the smallest?
Answer: Rolling friction
Detailed Explanation:
There are three main types of friction:
- Static friction – acts when the object is at rest
- Sliding friction – acts when surfaces slide over each other
- Rolling friction – acts when an object rolls over a surface
Why is rolling friction the least?
In rolling motion, the contact between surfaces keeps changing, so there is less rubbing compared to sliding.
Easy comparison:
Static > Sliding > Rolling
Examples:
- Wheels make movement easier
- Suitcases with wheels are easier to carry
Exam Line:
“Rolling friction is the least because surfaces do not continuously rub against each other.”
Q3. Using lubricants in machines?
Answer: Reduces friction
Detailed Explanation:
Lubricants such as oil and grease form a thin layer between two surfaces. This layer reduces direct contact, which decreases friction.
Advantages:
- Smooth working of machines
- Less heat production
- Reduced wear and tear
- Saves energy
Examples:
- Engine oil in vehicles
- Oiling moving parts of machines
- Exam Line:
- “Lubricants reduce friction by forming a thin layer between surfaces.”
Q4. Friction depends on?
Answer: Nature of surfaces
Detailed Explanation:
Friction mainly depends on:
1. Nature of surfaces
- Rough surfaces → more friction
- Smooth surfaces → less friction
2. Force pressing the surfaces
- Greater force → more friction
Examples:
- Walking on a rough road is easier
- Walking on ice is slippery
Exam Line:
“Friction depends mainly on the nature (roughness or smoothness) of the surfaces in contact.”
Q5. Fluid friction is also known as?
Answer: Drag
Detailed Explanation:
Fluids include both liquids and gases (like water and air). When an object moves through a fluid, the fluid resists its motion.
Why is it called drag?
Because the fluid tends to pull the object backward, opposing its motion.
Examples:
- Air resistance on a moving car
- Water resistance while swimming
Extra Concept:
Vehicles and aeroplanes are designed in a streamlined shape to reduce drag.
Exam Line:
“Fluid friction is called drag because it opposes the motion of objects moving through fluids.”
Quick Revision (1-minute recap):
- Friction → Opposes motion
- Rolling friction → Least
- Lubricants → Reduce friction
- Depends on → Nature of surfaces
- Fluid friction → Drag