Chapter 9 Friction Question Answers

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Important Terms to Learn Before Starting Making Notes 🗒

Ball Bearing (गेंद असर): A type of bearing that uses balls to maintain the separation between the bearing races, reducing rotational friction and supporting radial and axial loads.
Drag (घर्षण बल): The resistance force caused by the motion of a body through a fluid, such as air or water.
Fluid Friction (द्रव घर्षण): The resistance to motion experienced by an object moving through a fluid (liquid or gas).
Friction (घर्षण): The resistance that one surface or object encounters when moving over another.
Interlocking (अंतर्व्यापी): The meshing or fitting together of parts or surfaces that helps to resist motion.
Lubricants (स्नेहक): Substances applied to surfaces to reduce the friction between them, such as oil or grease.
Rolling Friction (लुढ़कने का घर्षण): The resistance to motion experienced by an object rolling over a surface.
Sliding Friction (फिसलन घर्षण): The resistance to motion experienced by an object sliding over a surface.
Static Friction (स्थैतिक घर्षण): The frictional force that prevents two surfaces from sliding past each other.

Exercise Question Starts Here: Start Working 🖊️

1. Fill in the blanks.

(a) Friction opposes the motion (गति) between the surfaces in contact with each other.

(b) Friction depends on the nature (स्वभाव) of surfaces.

(c) Friction produces heat (ऊष्मा).

(d) Sprinkling of powder on the carrom board reduces (घटाता है) friction.

(e) Sliding friction is less (कम) than the static friction.

2. Arrange Forces Due to Rolling, Static, and Sliding Frictions in a Decreasing Order.

(c) static, sliding, rolling

3. Alida Runs Her Toy Car on Different Surfaces. The Force of Friction Acting on the Car in Increasing Order Will Be

(a) wet marble floor, dry marble floor, newspaper, and towel.

4. Show the Direction of Frictional Force Acting on a Sliding Book

If a book starts sliding down on a tilted desk, the frictional force acts upwards (ऊपर की ओर) opposite to the direction of the book’s motion.

5. Effect of Spilling Soapy Water on Marble Floor

Spilling soapy water on a marble floor would make it more difficult (अधिक कठिन) to walk because the soap reduces friction, making the floor slippery.

6. Why Sportsmen Use Shoes with Spikes

Sportsmen use shoes with spikes to increase friction (घर्षण बढ़ाना) between their shoes and the ground, which helps them run faster and prevents slipping.

7. Who Will Have to Apply a Larger Force: Iqbal or Seema?

Seema will have to apply a larger force (अधिक बल) because a heavier box has more friction with the floor than a lighter box.

8. Why Sliding Friction is Less than Static Friction

Sliding friction is less than static friction because it is easier to keep an object moving than to start moving it from rest. Static friction acts when the object is not moving and is generally higher.

9. Examples Showing Friction is Both a Friend and a Foe

Friend (मित्र):

  • Friction allows us to walk (चलना) without slipping.
  • Friction helps in writing (लिखना) with a pen or pencil.

Foe (शत्रु):

  • Friction causes wear and tear (घिसाव) of machine parts.
  • Friction produces unwanted heat (अनचाही ऊष्मा) in machines.

10. Why Objects Moving in Fluids Must Have Special Shapes

Objects moving in fluids like water or air must have special shapes (विशेष आकार) called streamlined shapes to reduce friction (घर्षण घटाना) or resistance from the fluid. This helps them move smoothly and quickly

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