Chapter 9 1 Work Power and Machines Work

Chapter 9. 1 Work, Power, and Machines

Work is defined as a quantity that measures the effects of a force acting over a distance – if nothing gets moved from one place to another, there is NO WORK DONE!

Work Equation W=F X d Work = force x distance Units: Force = Newtons Distance = meters, kilometers Work – Joules

Power is calculated • Power = work/time • • P = __W___ T • and is measured in watts (W) • make sure it’s a capital “W”

What is a JOULE? • Just like Newton means kg m/s 2 • Joule means the same as 1 N–M • (1 Newton-Meter) meaning the amount of work done lifting something with a weight of 1 Newton through a distance of 1 meter.

Power • defined: quantity that measures the rate at which work is done. • i. e. , (how fast!) • If we both do the same work, but you do it faster, you are more “powerful”

Mechanical Advantage • Simply put, it’s how much help we get from the machine. • How much the machine “multiplies” our • efforts. • Or how much it increases our distance. • (think about how little your wrist moves when bat, and how wide the other end of the bat swings through the air.

Mechanical Advantage Equation • either • output force • input force or • INPUT is what you do • OUTPUT is the work that gets done, • thanks to the machine’s help! input distance output distance

Example Problem: A crate of bananas weighing 3000 N is lifted using a pulley. If 500 N of force is applied (the effort force), what is the mechanical advantage of the pulley? M. A. (mechanical advantage) = Force out / Force in So, M. A. = 3000 N / 500 N = 6 This means that the force needed to lift the crate is reduced by 6 times the weight of the crate.

Example : A screwdriver is used to open a can of paint. The distance that the arm is moved downward is 4 cm, while the lid moves 0. 5 cm before popping open. M. A. = distance in / distance out M. A. = 4 cm /. 5 cm = 8

The Inclined Plane (Ramp or screw) - reduces the effort force needed by increasing the distance through which the force is applied. 10 m 2 m The ideal mechanical advantage is equal to the length of the run divided by the height of the rise. M. A. = 10 m / 2 m = 5

Another way to calculate the mechanical advantage: M. A. = Force out / Force in Example: A 3500 N piano is moved up a small fight of stairs by using a ramp. If the piano movers only push with a force of 500 N, what is the mechanical advantage? M. A. = 3500 N / 500 N = 7