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Fizyka - program rozszerzony I

Lekcja 7: Moc

Podsumowanie wiadomości na temat mocy

Kluczowe pojęcia i definicje związane z pojęciem mocy. Różnica pomiędzy mocą i pracą.

Term (symbol)	Meaning
Power ( $P$ ‍)	Rate at which work is done (or energy is transferred). SI units of $Watts (W)$ ‍
Watt ( $W$ ‍)	Power equivalent to transferring $1 joule$ ‍ of energy per second. SI units of $\frac{kg \cdot m^{2}}{s^{3}}$ ‍

Equation	Symbols	Meaning in words
$P = \frac{Δ E}{Δ t}$ ‍	$P$ ‍ is power, $Δ E$ ‍ is change in energy, and $Δ t$ ‍ is change in time.	Power is the change in energy over the change in time.
$P = \frac{W}{Δ t}$ ‍	$W$ ‍ is work	Power is the work done over the change in time.

Some people confuse energy with power. Energy is a measurement of work done, while power is how energy changes with time.
Sometimes people forget that we can measure power by the work done by a force. We can substitute the work done by a force $W = F Δ x \cos θ$ ‍ instead of change in energy into the equation

\begin{aligned} P & = \frac{Δ E}{Δ t} \\ = \frac{W}{Δ t} \\ = \frac{F Δ x \cos θ}{Δ t} \end{aligned}

If the force is along the direction of motion, then

\cos θ = 1

and the equation can be re-written

P = F \bar{v}

where

F

is a constant force, and a change in distance over time is average velocity,

\bar{v}

For deeper explanations, see our video introducing power.

To check your understanding and work toward mastering these concepts, check out the exercise on relating power and energy.

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