Power Is Energy Divided by Time

Lab Brief #3

🎯 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

Power P = E/t is measured in watts, one watt being one joule per second. A 500 N student climbing 3 m of stairs does 1,500 J of work whether they stroll or sprint; taking 10 s means 150 W, taking 5 s means 300 W. Work measures the job done and power measures how quickly it was done — the same distinction that lets a small motor lift a heavy load eventually, but only a large one lift it fast.

Key words

power
The rate of energy transfer, equal to energy divided by time and measured in watts.
watt
The unit of power: one joule of energy transferred every second.

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

bathroom scales
tape measure
stopwatch
staircase

⚠️ Safety first

Use the handrail and do not run on wet or crowded stairs.

Step 1 of 4 · Read

Think about what you just learned: say what "power" and "watt" mean in your own words before you start.

Step 2 of 4 · Do

Measure your weight in newtons, then the vertical height of a staircase. Time yourself walking up and then running up, and calculate the work done and your power output in watts for each. Compare the two powers and check the work done is the same.

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 student does 1,500 J of work in 5 s. Their power output is:

How sure are you?😐 maybe

Question 2 of 3

One watt is equal to:

How sure are you?😐 maybe

Question 3 of 3

Walking and running up the same stairs differ in:

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.

Next: Efficiency and the Sankey Picture All lessons

🎯

Next Smart Experiment

We'll pick an experiment that matches exactly how you're thinking right now.

✨ More to explore

🌍 Where you see this in real life: This is why airplanes can fly and why rockets reach space.

🏆 Stretch challenge (try it this week): This week, find one thing in your house that turns one kind of energy into another.

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

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