Class 11 Physics Practical Coefficient of Friction Experiment Explained

🧪 Aim

To find the coefficient of friction between a wooden block and a horizontal surface and to study how limiting friction varies with normal reaction.

📌 Materials Required

• Horizontal plane
• Wooden block with hook
• Spring balance (0–500 g)
• Frictionless pulley
• Fine thread
• Scale pan
• Spirit level

📘 Theory (Explained Simply)

Whenever two surfaces touch, friction tries to stop motion.

• Static friction: Opposes motion before the object starts moving
• Kinetic friction: Acts after motion starts and is usually smaller
• Limiting friction: Maximum static friction, just before the block moves

F1 = μ1N Where:

• μ1 = coefficient of friction
• F1 = limiting friction
• N = normal reaction

🧭 Procedure

1. Place the horizontal plane on a table and level it using the spirit level.
2. Tie one end of the thread to the hook on the wooden block.
3. Pass the thread over the frictionless pulley and attach the scale pan to the other end.
4. Add weights to the pan gradually.
5. Lightly tap the table and note the weight at which the block just begins to move.
6. Add a 50 g weight on the block and repeat.
7. Perform at least five trials and record all observations.

📝 Observations

📊 Result

The coefficient of friction μ1 is obtained using:

μ1 = F1/N

(Average the values from all trials for accuracy.)

⚠️ Precautions

• Ensure the pulley is truly frictionless
• Keep the plane perfectly horizontal
• The thread should be straight, horizontal, and taut
• The scale pan should not touch the table or sway excessively

❗ Possible Errors

• Slight tilt in the table
• Friction present in the pulley
• Thread may sag or not remain horizontal
• Inconsistent tapping or adding weights too fast