Back to Energy

**Table of Contents**

##### Energy and Power

*Power*is the rate of doing work or, equivalently, the rate of using or producing energy.- Power is
*Energy or Work divided by Time*. - Power can also be expressed as
*Force times Velocity*,:**Power = (F x D) / T = F x (D/T) = F x V.**

- Power is
- Sentences referring to
*energy*and*work*:- We used 500 Kilowatt-hours of electrical energy last month
- It takes 600 foot-pounds of work to lift a 100 pound weight 6 feet in the air

- Sentences referring to
*power*:- This 10 watt LED bulb uses electrical energy at the rate of 10 joules per second
- My portable electric generator has a power output of 1600 watts, that is, 1600 joules per second.

- Analogies for distinction between
*energy*and*power*- How far you ran (energy) vs how fast you ran (power)
- How much you ate (energy) vs how fast you ate (power)
- Energy is stuff. Power is how fast you make or use the stuff.

**Units of Energy**

**Joule (J)**- force x distance (N x m)
- 1 joule = 1 newton x 1 meter

- mass x velocity
^{2}- 1 joule = 1 kg x 1 (m/s)
^{2 }

- 1 joule = 1 kg x 1 (m/s)

- force x distance (N x m)
**Foot-pound (ft-lb)**- force x distance = (lbf x ft)
- 1 ft-lb = 1 pound-force x 1 foot = 1.356 joules

- force x distance = (lbf x ft)
**Kilowatt-hour (kW⋅h)**- power x time = (energy / time) x time = (kW x h)
- 1 kW⋅h = 1000 watts x (60 x 60) seconds = 3.6 million joules

- power x time = (energy / time) x time = (kW x h)
**Electron volt (eV)**- volt x electric charge = (energy / charge) x charge

**Units of Power**

**Units of Power**

**Watt (W**)- Energy / time (J/s)
- 1 W = 1 joule of work done per second
- 1 W = 1 joule of energy produced or used per second

- Energy / time (J/s)
**Horsepower (hp)**- Energy / time (ft-lb/minute)
- 1 hp = 33,000 foot-pounds of work per minute
- 1 hp = 745.7 watts

- Energy / time (ft-lb/minute)

**Calculators**

**Calculators**- Energy
- Power