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Force, Work, and Energy - Simple Machines

Grade 3ICSE

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

🔑Concepts

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Force is a push or a pull applied to an object. It can change the shape, speed, or direction of an object.

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Work is said to be done only when a force applied to an object causes it to move a certain distance. If there is no movement, no work is done mathematically: Work=0\text{Work} = 0.

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Energy is the ability or capacity to do work. We get energy from various sources like the Sun (Solar Energy), Wind, and Food.

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Simple Machines are basic tools that make our work easier by changing the direction or the amount of force needed.

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The six types of simple machines are: Lever, Inclined Plane, Pulley, Wheel and Axle, Screw, and Wedge.

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An Inclined Plane is a slanting surface used to move heavy loads upwards with less effort, represented by the angle θ\theta of the slope.

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A Pulley consists of a grooved wheel and a rope used to lift objects, often changing the direction of the force from upward to downward.

📐Formulae

Work=Force×Distance\text{Work} = \text{Force} \times \text{Distance}

Work=F×d\text{Work} = F \times d

Energy=Capacity to do Work\text{Energy} = \text{Capacity to do Work}

💡Examples

Problem 1:

Rohan pushes a heavy stone wall with a force of 50 N50\text{ N} for ten minutes, but the wall does not move. Calculate the work done.

Solution:

Work=50 N×0 m=0 Joules\text{Work} = 50\text{ N} \times 0\text{ m} = 0\text{ Joules}

Explanation:

In science, work is only done if the object moves. Since the wall's displacement is 0 m0\text{ m}, the total work done is zero.

Problem 2:

A worker uses a ramp (inclined plane) to push a box to a height of 2 m2\text{ m} instead of lifting it straight up. Why is this easier?

Solution:

The inclined plane increases the distance over which the force is applied, reducing the effort required.

Explanation:

By using a slope, the worker applies a smaller force over a longer distance to achieve the same amount of work.

Problem 3:

Identify the simple machine used in a pair of scissors.

Solution:

Lever

Explanation:

A pair of scissors consists of two levers joined at a fixed point called the fulcrum. When you apply force at the handles, it cuts the paper at the other end.