Mechanical Advantage Multiplies Force, Never Work

Lab Brief #7

🎯 Your mission

Run the experiment. Find out what really happens.

⚡ The twist

The opposite of what you expect is often what happens.

What you'll learn

A machine can multiply force but it cannot create energy, so the output work can at best equal the input work. Multiply the force by four and you divide the distance by four: a 100 N pull moving 4 m puts in 400 J, and a mechanical advantage of four lifts 400 N through 1 m — also 400 J. Real machines fall short of that because friction dissipates some of the input, which is why efficiency is defined as useful output energy divided by total input energy and is always below 100%.

Key words

mechanical advantage
Output force divided by input force — how many times a machine multiplies the force applied to it.
efficiency
Useful output energy divided by total input energy, expressed as a percentage.

Make a hypothesis first

Predict: what happens if you double the force?

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

pulleys
string
newton meter
slotted masses
clamp stand
ruler

Get ready

⚠️ Safety first

Clamp the stand to the bench so it cannot topple, and keep feet clear of hanging masses.

Step 1 of 4 · Read

Think about what you just learned: say what "mechanical advantage" and "efficiency" mean in your own words before you start.

Step 2 of 4 · Do

Lift a 5 N load with a single pulley, then with a two-pulley and a four-pulley system. For each, measure the force on the string and the length of string you pulled through, and compare input work with output work to find the efficiency.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 3

A machine with a mechanical advantage of 4 lifts a load 1 m. The input force must move through:

How sure are you?😐 maybe

Question 2 of 3

Efficiency is defined as:

How sure are you?😐 maybe

Question 3 of 3

Why is a real machine's efficiency always below 100%?

How sure are you?😐 maybe

Mind = blown

🎢 You feel weightless on a roller coaster because you and the seat are falling at the same speed.

Nice work!

You got 0 of 3 right.

All lessons

🎯

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✨ More to explore

🌍 Where you see this in real life: You use this every time you flip a light switch, ride a bike, or kick a ball.

🏆 Stretch challenge (try it this week): Time how long a small ball rolls down something, then change the slope and try again.

👨‍👩‍👧 For the dinner table: “Show me something at home that uses this kind of energy.”

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Mechanical Advantage Multiplies Force, Never Work

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