How Machines do WORK A Machine – is a device that allows you to do work in a way that is easier or more effective. INPUT FORCE – is the force you exert on the machine. The distance the machine moves due to this force is the INPUT DISTANCE. OUTPUT FORCE – is the force a machine exerts on an object. The distance the machine exerts a force on is the OUTPUT DISTANCE.

INPUT WORK = input force x input distance OUTPUT WORK = output force x output distance AND INPUT WORK = OUTPUT WORK SO input force x input distanceoutput force x output distance =

There are 3 ways a machine can help make work easier : 1 – Machine increases Force: *A machine can lower the input force and increase the output force. *But there is an increase in input distance INPUT WORK = OUTPUT WORK SMALL INPUT FORCE LARGE OUTPUT FORCE LARGE INPUT DISTANCE SMALL OUTPUT DISTANCE EXAMPLES: using a ramp increases the total distance that has to be covered but decreases the input force.

2 – Machine Increases Distance: *A machine can raise the input force and decrease the output force. *But there is an increase in output distance INPUT WORK = OUTPUT WORK LARGE INPUT FORCE SMALL INPUT DISTANCE SMALL OUTPUT FORCE LARGE OUTPUT DISTANCE EXAMPLES: Riding a bike in high gear, swinging a baseball bat, using chopsticks

3 – Machine Changes Direction: *Input and output forces remain the same *input and output distances remain the same *only DIRECTION changes ! INPUT WORK = OUTPUT WORK EXAMPLE: Using a weight machine makes it easier to lift weights because it is easier to pull down than lift up.

MECHANICAL ADVANTAGE Mechanical Advantage - is the number of times a machine increases a force you exerted on it. Mechanical Advantage = Output Force Input Force OR Load Effort

Increasing Force: When the output force is greater than the input force, the mechanical advantage is greater than 1. Output Force = 30 N = 3 Input Force 10 N Increasing Distance: When the machine increases the distance, the mechanical advantage is less than 1. Output Force = 5 N = 0.5 Input Force 10 N

Changing Direction: When the output force is the same as the input force, the mechanical advantage is always equal to 1. Output Force = 30 N = 1 Input Force 30 N

Efficiency of Machines *In reality, the output work of a machine is always less that the input work because of FRICTION! *In every machine, some work is wasted overcoming the force of friction. The less friction there is, the closer the outcome work is to the input work. Efficiency = Output work x 100% Input work *The higher the percent, the more efficient a machine is!!!

Calculating Efficiency of Machines 1 – You do 20 J of work while using a hammer. The hammer does 18 J of work on a nail. What is the efficiency of the hammer? Efficiency = Output work x 100% Input work 18J x 100% = 90% 20J

Real and Ideal Machines Ideal machine: Efficiency = 100% Real machine: Efficiency ‹ 100% Because there is always some work wasted on overcoming friction