View Single Post
Nov27-12, 01:25 AM
P: 5

getting confused about watt vs watt.hour

in the Watt's wiki page, an example is given on how to calculate wattage (power):

A person having a mass of 100 kilograms who climbs a 3 meter high ladder in 5 seconds is doing work at a rate of about 600 watts. Mass times acceleration due to gravity times height divided by the time it takes to lift the object to the given height gives the rate of doing work or power
So, (100kg x (9.81m/s2) x 3m) / 5s = 588 kg.m2/s3

this system needs aroud 600 watts of power to accomplish its task. ok.

Then, lower in the page, an example is given on how to calculate watt.hour(energy):

For example, when a light bulb with a power rating of 100W is turned on for one hour, the energy used is 100 watt-hours (Wh), 0.1 kilowatt-hour

Now, if I go back to my first example, it's being done in 5 seconds for 588,6 watts

if it was done in 1 second, it would be 2943 watts

if it was done in 3600 seconds, it would be 0,8175 watts

So, if I do the work on a 1 hour (3600 sec) time span, can say I use 0,8175 watt.hour?

And if I lift the thing in 1 second, but constantly, for 1 hour, do I use 2943 watt.hour?

This is confusing me a little, so I guess my question also is a little confused. I looked many places where it was promised that this confusion would evaporate after reading their explanations. Now I'm here because I'm still a little lost.

Phys.Org News Partner Physics news on
Symphony of nanoplasmonic and optical resonators produces laser-like light emission
Do we live in a 2-D hologram? New Fermilab experiment will test the nature of the universe
Duality principle is 'safe and sound': Researchers clear up apparent violation of wave-particle duality