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Machines

ICSE Grade 10 Physics - Chapter 3

📚 Smart Summary

1. Introduction to Machines

Machine: A device that makes work easier by changing the magnitude or direction of force.

Simple Machines: Lever, pulley, inclined plane, wheel and axle, wedge, and screw.

Purpose: Machines help multiply force, change direction of force, or gain speed.

Input and Output: Effort (input force) and Load (output force).

Real vs Ideal Machines: Real machines have friction and energy losses; ideal machines have 100% efficiency.

2. Mechanical Advantage (M.A.)

Definition: The ratio of load to effort. M.A. = Load/Effort.

Meaning: Indicates how many times a machine multiplies the effort force.

Unit: M.A. has no unit (it's a ratio).

M.A. > 1: Machine multiplies force (force multiplier).

M.A. < 1: Machine multiplies speed (speed multiplier).

M.A. = 1: Machine only changes direction of force.

3. Velocity Ratio (V.R.)

Definition: The ratio of the velocity of effort to the velocity of load. V.R. = Velocity of Effort / Velocity of Load.

Alternative Definition: V.R. = Distance moved by effort / Distance moved by load.

Characteristic: V.R. is constant for a given machine and depends only on its geometry.

Unit: V.R. has no unit (it's a ratio).

Ideal Machine: For an ideal machine, M.A. = V.R.

4. Efficiency (η)

Definition: The ratio of useful work output to total work input. η = (Work Output / Work Input) × 100%.

Formula: η = (M.A. / V.R.) × 100%.

Range: Efficiency is always less than 100% for real machines due to friction and other energy losses.

Factors Affecting Efficiency: Friction, design of machine, lubrication, and material quality.

Ideal Machine: Would have 100% efficiency (M.A. = V.R.), but impossible in practice.

5. Levers

Lever: A rigid rod that can rotate about a fixed point called fulcrum.

Three Classes of Levers: Based on positions of fulcrum (F), effort (E), and load (L).

Class I: Fulcrum between effort and load (F-E-L). Examples: seesaw, crowbar, scissors.

Class II: Load between fulcrum and effort (F-L-E). Examples: wheelbarrow, nutcracker, bottle opener.

Class III: Effort between fulcrum and load (F-E-L). Examples: tweezers, fishing rod, human forearm.

6. Pulleys

Pulley: A grooved wheel that rotates about an axle, with a rope running over it.

Single Fixed Pulley: M.A. = 1, V.R. = 1. Used only to change direction of force.

Single Movable Pulley: M.A. ≈ 2, V.R. = 2. Provides mechanical advantage.

Block and Tackle System: Combination of fixed and movable pulleys. V.R. = number of supporting strings.

Applications: Cranes, elevators, flag poles, and wells.

📐 Formulas

Mechanical Advantage (M.A.) = Load / Effort

Ratio of output force to input force

Velocity Ratio (V.R.) = Distance moved by Effort / Distance moved by Load

Ratio of distances or velocities

Efficiency (η) = (M.A. / V.R.) × 100%

Percentage efficiency of a machine

Efficiency (η) = (Work Output / Work Input) × 100%

Alternative formula for efficiency

🎯 Test Your Knowledge

Multiple Choice Questions

1. The mechanical advantage of a machine is defined as:

2. The velocity ratio of a machine depends on:

3. The efficiency of a real machine is always:

4. A single fixed pulley has a mechanical advantage of:

5. In which class of lever is the fulcrum between the effort and the load?

6. A wheelbarrow is an example of:

7. For an ideal machine:

8. If the efficiency of a machine increases, which of the following must be true?

9. Assertion (A): A machine with M.A. less than 1 is useless. Reason (R): Such machines are used as speed multipliers.

10. The V.R. of a block and tackle system is equal to:

Practice Numericals

Practice Problem 1: A machine lifts a load of 300 N with an effort of 50 N. Calculate its mechanical advantage.

Practice Problem 2: A lever has a V.R. of 4 and lifts a load of 200 N with an effort of 60 N. Calculate its efficiency (as a percentage).

Practice Problem 3: A pulley system has 5 supporting strings. If an effort of 80 N is applied to lift a load of 360 N, find the mechanical advantage.

Practice Problem 4: A machine with V.R. = 6 requires an effort of 150 N to lift a load of 750 N. Calculate its efficiency (as a percentage).

Practice Problem 5: An inclined plane of length 10 m is used to raise a load to a height of 2 m. Find its velocity ratio.