Weight Is Not Mass

Lab Brief #4

🎯 Your mission

Predict it first. Then prove yourself right (or wrong).

⚡ The twist

The opposite of what you expect is often what happens.

What you'll learn

Mass is the amount of matter, in kilograms, and does not change with location. Weight is the gravitational force on that mass, in newtons, and equals mg. A 60 kg astronaut still has 60 kg of mass on the Moon but weighs about a sixth as much.

Key words

weight
The force of gravity on a mass, W = mg, measured in newtons.
gravitational field strength
The force per kilogram at a point, about 9.81 N/kg on Earth.

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

newton meter
slotted masses
clamp stand
graph paper

⚠️ Safety first

Secure the clamp stand with a counterweight so it cannot topple.
Keep feet clear beneath hanging masses.

Step 1 of 4 · Read

Think about what you just learned: say what "weight" and "gravitational field strength" mean in your own words before you start.

Step 2 of 4 · Do

Hang known masses from a newton meter and record the reading for each. Plot weight against mass, find the gradient, and identify it as the local gravitational field strength.

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 2

A 60 kg astronaut travels to the Moon. Her mass there is:

How sure are you?😐 maybe

Question 2 of 2

Weight is measured in:

How sure are you?😐 maybe

Mind = blown

🔥 A bolt of lightning is 5 times hotter than the surface of the sun.

Nice work!

You got 0 of 2 right.

Next: Free-Body Diagrams 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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