Explanation of the concepts **work**, **energy** and **power** known from physics.

# Work (Arbeit)

- Unit: J (joule), Nm (newton-metre), cal (calorie), Ws (watt-second), kWh (kilowatt-hour)
- “Moving a mass over a distance”
- $W = F \, s$ (work is force times distance)
- Example:
- Force: $F = 10 \text{N}$
- Distance: $s = 2 \text{m}$
- Work: $W = F \, s = 20 \text{Nm} = 20 \text{J}$

- Equivalences: $1 \text{J} = 1 \text{Nm} = 1 \text{Ws}$
*Analogy with distance (120 km)*

# Energy (Energie)

- Unit: J (joule), Nm (newton-metre), cal (calorie), Ws (watt-second), kWh (kilowatt-hour)
- “Capacity to do work”
- Equivalent to work

# Power (Leistung)

- Unit: W (watt), hp (horsepower), dBm (decibel-milliwatt)
- “Amount of work done per time”
- “Rate of doing work”
- “Energy consumed per time”
- “Light bulb wattage: rate at which the light bulb converts electrical energy into light and heat”
- $P = \frac{W}{t}$ (power is work divided by time)
- Examples:
- Doing 500 Nm work in 5 sec.: $P = \frac{500\text{Nm}}{5\text{s}} = 10\text{W}$
- Doing 500 Nm work in 1 hour: $P = \frac{500\text{Nm}}{3600\text{s}} = 0.134\text{W}$
- 40 W light bulb: amount of energy used in 1 hour: $E = 40\text{W} \cdot 3600 \text{s} = 144000 \text{J}$

- Equivalences:
- $W = \frac{\text{J}}{\text{s}}$
- $1 \text{hp} \approx 740 \text{W}$

*Analogy with speed (30 km/h)*