lesson
Rate of transfer differs from amount transferred
1 · Learn
Work done by a force along a displacement is force times distance in that direction in the simple constant-force case. Power is energy transferred per second. A device can transfer the same total energy more quickly by operating at greater power.
Joules measure energy and watts measure power. A high power rating does not by itself state total energy use without an operating time.
2 · Worked example
Transferring 600 J in 20 s gives average power 30 W. The same energy in 10 s gives 60 W.
3 · Your turn
A device transfers 900 J in 30 s. Find its average power.
Check your answer
30 W.
4 · Apply your learning
Compare two devices using both power and duration, explicitly stating the idealised constant-power assumption.
Adult guidance and safety
Use supplied evidence and approved models. Practical science needs a qualified adult, appropriate equipment and a risk assessment. Do not attempt chemical reactions, heating, mains electricity or solar observation independently. Never request personal health or genetic disclosures.
Open your writing and drawing pad
Write, draw or show your working. Use a mouse, pen or finger. This pad is not a submitted answer.
Not saved to your account. Download your drawing as PNG and your typed notes as TXT before leaving or refreshing. They are separate files. Do not enter private information.
Open a picture saved on this device to draw on it again. Opening replaces the drawing, but Undo can restore it. PNG only, up to 4 MB and 4096 × 4096 pixels. The picture stays in this browser; it is not uploaded. Paper lines in a saved picture become part of that picture.
Clear the drawing? Your typed notes will stay. You can undo this action.
Your pad is empty.
Open a UTF-8 TXT file from this device, up to 40 KB and 10,000 characters. It stays in this browser. Opening can be undone until you type again. Downloads keep a new copy; they do not change the file you opened.
Replace the notes on this page with the opened file? Download the current notes first if you want to keep them.
Typed notes are not submitted answers.
Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
My observation notebook
Follow your teacher's approved method and safety instructions. Record the sample or supplied dataset, conditions, measurements with units and uncertainties where appropriate. Distinguish observations from explanations. A described experiment is not permission to carry it out; do not improvise equipment or invent missing results.
Ask your teacher for support with the method and recording. A prediction is what you think might happen; an observation is what you actually see, hear or feel safely.
Keep your notebook: use Download notebook before leaving. Nothing is sent to the website or saved to your account. Reopen the downloaded notebook here to add another day's record. Do not include names, addresses or other private information.
Your records on this page
No observations recorded yet. Look first, then add one.
Reopening adds records; it does not replace your current records. Up to 50 records per notebook. Keep your downloads somewhere private. Editing this notebook does not submit work or complete a lesson.
Practice this lesson
Lesson resources
Browse the available practice activities and worksheets for this lesson.
Your progress