Overview
This lecture explains how energy is transferred as work, the meaning of power, and how to calculate power using work done and time.
Energy Transfer and Work
- Work done on an object is a way energy is transferred.
- Energy allows work to be done in physical systems.
Power and Its Calculation
- Power is the rate at which energy is transferred or work is done.
- Power is measured in watts (W), where 1 W = 1 joule per second (J/s).
- The equation for power is: Power = Work done ÷ Time taken (P = W / t).
- A device with higher power transfers more energy every second.
Worked Example
- Lifting a 2 N weight by 10 m requires 20 J of work (W = F × d = 2 × 10).
- Motor one does this in 5 s: Power = 20 J ÷ 5 s = 4 W.
- Motor two does this in 10 s: Power = 20 J ÷ 10 s = 2 W.
- Motor one is twice as powerful as motor two because it transfers energy faster.
Example Problem
- A hairdryer transfers 48,000 J in 1 minute (60 s): Power = 48,000 ÷ 60 = 800 W.
Key Terms & Definitions
- Energy — The ability to do work or cause change.
- Work done (W) — Energy transferred when a force moves an object (in joules, J).
- Power (P) — The rate of energy transfer or work done per unit time (in watts, W).
- Watt (W) — Unit of power; equals one joule per second (J/s).
- Joule (J) — Unit of energy or work.
Action Items / Next Steps
- Practice calculating power using the formula P = W / t with different values.
- Review the next section on efficiency for further understanding.