Warm Up: 1/14/13  Give an example of a machine you use on a daily basis. Then say how you thinks it helps to make work easier.

MACHINES Chapter 8, Sections 2

What is a machine?  a device that makes work easier by changing the size or direction of a force.  Imagine trying to change a tire without a jack or tire iron  Everyday machines: Wheel chair Chopsticks Scissors

Work and Machines  Work Input: the work that you do on a machine  You apply an input force through a distance on a machine.  Work Output: the work done by the machine  The machine applies an output force through a distance  Example: We use a can opener to help open a jar. What is the input? What is the output?

Do machines for work for us??  No, Work output is ALWAYS less than work input.  Machines do not make work less, just EASIER.  How?  Some machines allow force to be applied over a greater distance, so less force is needed to do the work. But you have to go a longer distance so you still have to do more work than the machine!  EX: when loading something into a truck. If you push it up a ramp it will be easier. You need less force but must go a farther distance.

Why is work output always less than work input?  All machines have moving parts that create friction as they move.  SO: some work input always goes into overcoming friction in the machine therefore reducing the work output.

How do machines make work easier?  When using a machine 3 things could happen…  1. The machine could increase your force by decreasing your distance. (ex. Ramp)  2. The machine could decrease your force but increase your distance. (ex. Baseball Bat or Feather Duster)  3. The machine could change the direction of your input force. (ex. Flagpole)

Mechanical Advantage  The number of times the machine multiplies the force. It compares the output and input force.  MA = output force / input force  MA > 1 means the machine makes lifting or moving a heavy object easier.  MA < 1 means the machine can still help, it just reduces the output force.

Mechanical Efficiency  A comparison of a machines work output to its work input.  ***the less work a machine must do to overcome friction, the more efficient it is.  ME = (work output/work input) x 100 Your answer will be a percentage  Ideal efficiency would be 100% However due to friction this cannot be done. What can be done to REDUCE friction? Use lubricants such as oil or grease

1 meter 3 meters 2000 N Effort Force = 800 N Work Input = F i x D i Work Ouput = F o x D o

Calculating Advantage and Efficiency  Efficiency = (Work Output/Work Input) x 100  E = (2000/2400) x 100  E = 0.83 x 100  E = 83.3 %  Mechanical Advantage = Force Output/Force Input  MA = 2000N/800 N  MA = 2.5

Machines Help us in 3 Ways  The machine may: 1. Multiply the input force by increasing the input distance 1. Meaning you use less force but more distance – the machine uses more force and less distance 2. Multiply the input distance by increasing the input force 1. Meaning you use more force and less distance – the machine uses less force and more distance 3. Change the direction of the input force

☺ Lever ☺ Pulley ☺ Wheel and Axle ☺ Inclined Plane ☺ Wedge Types of Simple Machines Chapter 8, Section 3

The Pulley  A machine that consists of a grooved wheel that holds a rope or cable.  A load is attached to one end of the rope, an input force applied to the other end.

Fixed Pulley  This pulley is attached to something that does not move.  It changes the direction of the input force.  Pulling down on the rope pulls the load up.

Movable Pulley  This pulley is attached to the object being moved.  It does NOT change the direction of the force  It increases force by increasing the distance the work is done over.

Block and Tackle Pulley  When a fixed pulley and a moveable pulley are used together.  The mechanical advantage depends on the number of rope segments.

Wheel and Axle  Consists of two circular objects of different sizes  MA = radius of wheel / radius of axle  MA >1 means the radius of the wheel is larger than the axle.  Multiplies input force!

Inclined Plane  straight, slanted surface that helps us to do work.  Multiplies input force by spreading the work over a greater distance!  MA = length of ramp / height of ramp  The greater the ratio the greater the mechanical advantage

The Wedge  A type of inclined plane.  Consists of a pair of inclined planes that move.  Applies an output force that is greater than the input force, but the input force is over a greater distance.

Screw  An inclined plane wrapped around a cylinder.  Applies a small input force over a long input distance.  This increases output force but decreases distance.

The Lever  A simple machine that consists of a bar that pivots at a FIXED point, called a fulcrum.  There are 3 types…

1 st Class Lever  The fulcrum is between the input force (you) and the load (the work to be done)  This lever changes the direction of the input force  It may also increase force OR distance depending on the location of the fulcrum. Fulcrum Load Effort

2 nd Class Lever  The load is between the fulcrum and the input force.  This lever does NOT change the direction of the input force.  Allows you to apply less force over a longer distance.  Multiplies input force! Fulcrum EffortLoad

3 rd Class Lever  The input force is between the fulcrum and the load.  Does NOT change the direction of the input force or increase the size of the input force.  Allows for a small input distance but a large output distance.  Reduces input force in exchange for a greater output distance. Effort Load Fulcrum

Compound Machine  A machine made up of two or more simple machines.

Warm Up: 1/22/13  You apply a 90 N force on a lever which moves the lever 1.5 m. If the bookshelf weighs 175 N and it moves.75 m, what is the efficiency of the lever?