Work and Power Notes

What is work ?  The  The product of the force applied to an object and the distance through which that force is applied.

Is work being done or not?  Mowing  Mowing the lawn  Weight-lifting  Moving  Moving furniture up a flight of stairs  Pushing  Pushing against a locked door  Swinging  Swinging a golf club  YES  NO  YES

Calculating Work All or part of the force must act in the direction of the movement.

Work Triangle Formulas  W=?  W=F x d  F=?  F = W / d  d=?  d = W / F

Do you do more work when you finish a job quickly?  Work does NOT involve time, only force and distance.  No work is done when you stand in place holding an object.  Labeling work: w = F x d  Newton X meter (N m)  Which also = (kg x m 2 ) s 2 s 2

The Joule  1 newton-meter is a quantity known as a joule (J).  Named after British physicist James Prescott Joule.

 How quickly work is done.  Amount of work done per unit time.  If two people mow two lawns of equal size and one does the job in half the time, who did more work?  Same work. Different power exerted.  POWER = WORK / TIME

Power Triangle Formulas  P=?  P = W / T  W=?  W = P x T  T=?  T = W / P

The watt  A  A unit named after Scottish inventor James Watt.  Invented  Invented the steam engine.  P  P = W/t  Joules/second  1 watt = 1 J/s

watts  Used to measure power of light bulbs and small appliances  An electric bill is measured in kW/hrs.  1 kilowatt = 1000 W

Horsepower (hp) = watts  Traditionally associated with engines. (car,motorcycle,lawn-mower)  The term horsepower was developed to quantify power. A strong horse could move a 750 N object one meter in one second. 750 N

WorkPower Defined as “Applying a force a given distance“ Equation Work = Force x Distance Newton Meter which is a Kgm 2 /s 2 Short Name “JOULE” Defined as “Rate at which work gets done” Equation Power = Work / Time In other words Power = (F x D) ÷ time Units are Joules per second  “Watts” US units  Horsepower 1HP = 746 Watts