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Simple Machines - Levers and their classes

Grade 6ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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A lever is a simple machine consisting of a rigid bar that is free to turn about a fixed point called the fulcrum (FF).

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There are three main components in any lever: the Load (LL), the Effort (EE), and the Fulcrum (FF).

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The distance from the fulcrum to the point where the load acts is called the Load Arm (LALA), and the distance from the fulcrum to the point where the effort is applied is called the Effort Arm (EAEA).

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Principle of Levers: When a lever is in equilibrium, the clockwise moment of the load is equal to the anticlockwise moment of the effort, expressed as Load×Load Arm=Effort×Effort ArmLoad \times Load\ Arm = Effort \times Effort\ Arm.

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Mechanical Advantage (MAMA) is the ratio of the load to the effort. It can also be defined as the ratio of the effort arm to the load arm.

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Class I Lever: The fulcrum is located between the load and the effort (e.g., see-saw, scissors, crowbar). MAMA can be greater than, less than, or equal to 11.

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Class II Lever: The load is located between the fulcrum and the effort (e.g., wheelbarrow, nutcracker, bottle opener). MAMA is always greater than 11.

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Class III Lever: The effort is located between the fulcrum and the load (e.g., sugar tongs, fishing rod, human forearm). MAMA is always less than 11.

📐Formulae

Load×Load Arm=Effort×Effort ArmLoad \times Load\ Arm = Effort \times Effort\ Arm

MA=LoadEffortMA = \frac{Load}{Effort}

MA=Effort ArmLoad ArmMA = \frac{Effort\ Arm}{Load\ Arm}

💡Examples

Problem 1:

A lever of length 100 cm100\text{ cm} has its fulcrum at one end. A load of 50 kgf50\text{ kgf} is placed at a distance of 20 cm20\text{ cm} from the fulcrum. Calculate the effort required at the other end to lift the load.

Solution:

Given: L=50 kgfL = 50\text{ kgf}, LA=20 cmLA = 20\text{ cm}, EA=100 cmEA = 100\text{ cm}. Using the Principle of Levers: L×LA=E×EA  ⟹  50×20=E×100  ⟹  1000=E×100  ⟹  E=10 kgfL \times LA = E \times EA \implies 50 \times 20 = E \times 100 \implies 1000 = E \times 100 \implies E = 10\text{ kgf}.

Explanation:

Since the load is between the fulcrum and the effort, this is a Class II lever. The effort needed is significantly less than the load because the effort arm is much longer than the load arm.

Problem 2:

Calculate the Mechanical Advantage (MAMA) of a pair of sugar tongs if the effort is applied at a distance of 4 cm4\text{ cm} from the fulcrum and the load (sugar cube) is 10 cm10\text{ cm} from the fulcrum.

Solution:

EA=4 cmEA = 4\text{ cm}, LA=10 cmLA = 10\text{ cm}. MA=Effort ArmLoad Arm=410=0.4MA = \frac{Effort\ Arm}{Load\ Arm} = \frac{4}{10} = 0.4.

Explanation:

Sugar tongs are Class III levers. The MAMA is 0.40.4, which is less than 11. This means the machine acts as a speed multiplier rather than a force multiplier.

Levers and their classes - Revision Notes & Key Formulas | ICSE Class 6 Science