Work, Energy and Power

Overview

Students investigate how work transfers energy when a force moves an object, then use evidence and calculations to distinguish work from power. The lesson builds on prior learning about forces, energy stores and energy transfers.

Learning intentions

• WALT describe work as energy transferred by a force acting through a distance.
• WALT calculate work done using (W = Fd).
• WALT calculate power using (P = \frac{W}{t}).
• WALT explain how force, distance and time affect work and power.

Success criteria

• I can identify the force, distance and direction of movement in a situation.
• I can use correct units and calculate work done and power.
• I can explain the difference between doing more work and doing work more quickly.
• I can use evidence from an investigation to support my explanation.

Curriculum links

• Demonstrate understanding of a physical system using energy concepts: energy transfer, conservation of energy, mechanical energy and calculations.
• Demonstrate understanding of a physical phenomenon through investigation: collecting numerical data, processing it in tables or calculations, and explaining relationships.
• Science capabilities: thinking critically, using scientific language and symbols, and interpreting evidence.
• Key Competencies: thinking; managing self; participating and contributing; using language, symbols and texts.

Lesson structure (50 minutes)

1. 0–5 min · Hook and prior knowledge. Display a short comparison on the opening comparison of two students climbing stairs: one student climbs slowly and another quickly, then ask, “Who does more work? Who has greater power?” Students make an individual prediction and justify it to a partner using force, distance, energy or time.

2. 5–13 min · Direct teach: work. Use the work and energy transfer teaching slides to establish that mechanical work is done when a force causes an object to move in the direction of the force, with (W = Fd), measured in joules. Students annotate the work and power investigation worksheet by identifying force, displacement and units in two worked examples; clarify that holding an object still requires force but does not involve mechanical work because there is no displacement.

3. 13–28 min · Practical investigation. Set up groups of three with a spring balance, trolley or weighted object, metre ruler and stopwatch. Students use the worksheet table to investigate one or more lifts or pulls: measure the force, distance and time, calculate work done and power, and repeat measurements where possible. Assign roles of equipment manager, measurer and recorder, then rotate roles. Circulate and check that students read the spring balance correctly, measure displacement rather than path length, and record units.

4. 28–36 min · Process and compare data. Students complete calculations on the calculation and results section, including (W = Fd) and (P = \frac{W}{t}). Groups compare results with another group and discuss: “If the same work is done in half the time, what happens to power?” “Would a larger force always mean greater power?” Students identify one pattern and one limitation, such as friction, inconsistent timing or inaccurate measurements.

5. 36–45 min · Explain and apply. Model one calculation from a group’s data using correct substitution, units and significant figures appropriate to the measured data. Students answer the application questions on the explanation and application questions, including a staircase or lifting scenario. They write a CER response: claim, evidence from their data, and reasoning using work and power. Invite selected groups to share explanations and address common errors, especially confusing joules with watts.

6. 45–50 min · Plenary and exit check. Return to the final recap and exit-question slide and revisit the opening prediction. Students complete the final three questions on the exit check: define work, calculate the power when 600 J is transferred in 5 s, and explain why two people doing the same work can have different powers. Collect responses to identify next-lesson needs.

Resources

• the work, energy and power slide deck
• the work and power investigation worksheet
• Spring balances or force meters
• Trolleys or small weighted objects
• Metre rulers or tape measures
• Stopwatches or timer apps
• Calculators
• Clear floor or bench space
• Safety glasses if using additional equipment

Assessment

• Questioning during the hook and direct teaching checks whether students distinguish force from work and work from power.
• Observe group measurements, unit use and calculations; provide immediate feedback on displacement, repeated measurements and formula substitution.
• Use the exit check to assess whether students can calculate power and explain the relationship between work and time. Look for: work in joules, power in watts, and a clear evidence-based explanation.

Differentiation

• Provide a formula box, symbol-and-unit table, one fully worked example and sentence starters: “The work done is… because…” and “The power is greater when…”.
• Pair students strategically and allocate practical roles. Offer pre-recorded timer readings or teacher-measured values for students who need reduced equipment demands.
• Use dyslexia-friendly formatting: uncluttered worksheet layout, sans-serif font, generous spacing, high contrast, short instructions, diagrams beside text, and allow students to hear instructions or use text-to-speech.
• Support EAL learners with a visual word bank for force, displacement, work, energy, power, joule and watt; accept labelled diagrams and oral rehearsal before written responses.
• Advanced learners derive (P = \frac{Fd}{t}), investigate whether changing force or distance has the greater effect in a controlled comparison, and evaluate uncertainty using percentage difference between repeated trials.

Extension

• Challenge students to design a fair test comparing two ways of completing the same task, keeping work approximately constant while changing power.
• Ask students to explain why a highly powerful machine does not necessarily transfer more energy overall, using work, time and efficiency in their response.