Work formula...

[Externet]

Hi.
The formula for work I found in my old notes says:

W = P x t

Where W is work in Joules/second;
P is power in Watts;
t is time in seconds.

Is that right?

This other one I think is fine:

E = P x t

Where E = energy in Joules;
P = power in Watts;
t = time in seconds.

Miguel

<small>[ December 01, 2005, 09:14 PM: Message edited by: Externet ]</small>

[dyarker]

They can't both be right.
Both have Watts times Seconds on right side, Joules per Second on left for one and just Joules in the other.

[Chris Smith]

From the introduction to Physics:

"The work is done by a force that acts on a object as the object moves through a displacement".

Take you pick......[There are others]
Newton X Meter
Dyne X Centimeter
Pound X Foot

However time is not needed in the equation to formulate the equation of “Work”

[maja]

Power (P) is the amount of work done per unit of time.
It can be modeled as an energy flow equivalent to rate of change of the energy in a system, or the time rate of doing work. Power is in general terms defined:

P=dE/dt=dW/dt ; [watt]=[joule]/[second]

SI unit of E and W is joule

Miguel the mistake you have up there is: "Where W is work in Joules/second;" ie Unit of work is in joules and units are not written capitalized as names of the inventors are by standard that is.

<small>[ December 02, 2005, 03:46 AM: Message edited by: Maja ]</small>

[Will]

Your first expression is correct i.e. W = P x t
What is not correct is your definition of the units i.e. P x t is not equal to Joules/seconds which means Joules per second it is simply Joules i.e P = power = the rate of doing work = Watts = Joules/sec W = P x t = (Joules/sec)* seconds = Joules.
One Watt = one Joule per sec and one Joule - one Newton.metre i.e. the work done when a force of one Newton (The force required to accelerate one kilogram at the rate of one metre per second per second) acts through a distance of one metre.

[josmith]

If you multiply watts times seconds you get watt-seconds. One watt-second is the same as one joule. Work and energy have the same definition so you're good to go in both cases.

[Chris Smith]

Work is force times distance or displacment.

Quantitive work is force times distance over time.