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Forces and Energy - Simple Machines and Work

Grade 5IB

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

🔑Concepts

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Work is done when a force acts upon an object to cause a displacement. In science, if the object does not move, no work is done, regardless of how much force is applied.

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Force is a push or a pull exerted on an object, measured in Newtons (NN).

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Simple machines are devices with few or no moving parts that make work easier by changing the direction of a force or the amount of force needed.

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

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Mechanical Advantage is the trade-off between force and distance. For example, an inclined plane allows you to lift a heavy load using less force, but you must move it over a longer distance (dd).

📐Formulae

W=F×dW = F \times d

1J=1N×1m1 J = 1 N \times 1 m

F=WdF = \frac{W}{d}

💡Examples

Problem 1:

A student pushes a heavy box with a force of 20N20 N over a distance of 5m5 m. How much work has the student performed?

Solution:

W=20N×5m=100JW = 20 N \times 5 m = 100 J

Explanation:

To find the work done, we multiply the force (F=20NF = 20 N) by the distance (d=5md = 5 m). The resulting unit for work is Joules (JJ).

Problem 2:

If a machine performs 50J50 J of work to move an object 2m2 m, what was the force applied?

Solution:

F=50J2m=25NF = \frac{50 J}{2 m} = 25 N

Explanation:

By rearranging the work formula to solve for force, we divide the total work (W=50JW = 50 J) by the distance (d=2md = 2 m) to get a force of 2525 Newtons (NN).

Problem 3:

An inclined plane is used to slide a crate. If the crate weighs 100N100 N and is lifted 1m1 m vertically, compare this to sliding it 4m4 m along the ramp with a force of 25N25 N.

Solution:

Wvertical=100N×1m=100JW_{vertical} = 100 N \times 1 m = 100 J and Wramp=25N×4m=100JW_{ramp} = 25 N \times 4 m = 100 J

Explanation:

The total work done is the same (100J100 J) in both cases. However, the simple machine (inclined plane) makes the task easier by allowing a smaller force (25N25 N instead of 100N100 N) to be used over a longer distance (4m4 m instead of 1m1 m).