chapter 9.1 work, power, and machines. work is defined as a quantity that measures the effects of a...

Chapter 9.1Work, Power, and Machines

Work is defined asa 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 = NewtonsDistance = meters,

kilometersWork – 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/s2

• 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 or input distance

• input force output distance

• INPUT is what you do• OUTPUT is the work that gets done,• thanks to the machine’s help!

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 moves0.5 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.

The ideal mechanical advantage is equal to the lengthof the run divided by the height of the rise.

2 m10 m

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