14 1 Work And Power
- 1. 14.1 Work and Power When Does a Force Do Work? How Are Work and Power Related?
- 2. What is Work? Work is the product of force and distance For a force to do work on an object Some force must act in the same direction as the object moves. No movement = No work done Work requires motion
- 3. Work Depends on Direction Any part of force that does not act in the direction of motion Does no work on an object Work = Force X Distance Units of work = Joule Derived unit of Newton x Meter (N x m) (Name after James Prescott Joule 1818-1889)
- 4. What Is Power? Power = is the rate of doing work. Doing work at a faster rate requires more power. Increasing your power increases amount of work done in a given time.
- 5. Examples of Power Ex. Using a Snow blower compared to shoveling a walkway… Which is faster? The size of engine used by a machine indicates its power.
- 6. Calculate Power! Calculate Power: Power = Work / Time Units for Power = Watt (W) 40-watt light bulb requires 40 joules each second that it is lit. The same amount of energy is used to raise your book 1 meter high in half a second
- 7. James Watt and Horsepower Horsepower is another unit of power Horsepower (hp) is = to 746 watts James Watt first defined Watt was looking for a comparison for the steam engines he had invented. Used horse as they were used most in the 1700s
- 8. James Watt and Horsepower Defined the Horsepower based on the power output of a very strong horse. Ex. If you have a 4hp Rototiller it would get as much work done as a plow pulled by 4 horses.