2. POWER

3. Power What is power and how is it calculated? If you consider the amount of time it takes to do a particular amount of work, you are now talking about a concept of work called power. To calculate power you can consider what you already know about work, that W=f x d. Now put into the equation time and you have the formula. p = f x d t or p = w tw t

4. Units of Power If power is equal to work divided by time and work is measured in newton meters or joules and time is measured in seconds then the units for power would be Nm / s or J / s 1 Nm / s = 1 J / s either of these is equal to a unit of power called the watt (W) so = 1 W

5. Calculating Power #1. If 500 N of force is used to move a crate a distance of 20 m, and the job takes a total of 5 seconds, how much power is used?

6. The Answers #1 p= f x d t p = 500 N x 20 m 5 sec p = 2000 Nm/s or J (joules) or 2000 W

7. #2. If 2,000 watts of power are used to accomplish 40,000 J of work. How much time is needed to do this task?

8. The Answers #2 t = W p t = 40,000 J 2000 W t = 20 sec

9. Work and Power Reviewed Two criteria for work: - an object must move - force must be applied in the direction that the object moves Formulas For Work w = f x d For Power p = fxd t orp = w t Units Nm/s, J/s W (watts)

10. Work and Power Reviewed (units) for Work Force is in newtons (N) Distance is in meters (m). Work is in newton meters (Nm) Joule (J) 1 Nm = 1 J for Power Work is in Nm or J Time is in seconds (s) Power is in Nm/s or J / s or watts (W)

11. The End !