P. Sci. Unit 3 Machines

2 What’s work?  A scientist delivers a speech to an audience of his peers.  No  A body builder lifts 350 pounds above his head.  Yes  A mother carries her baby from room to room.  No  A father pushes a baby in a carriage.  Yes  A woman carries a 20 km grocery bag to her car?  No

Machine – a device that makes doing work easier by… Copy this

 increasing the force that can be applied to an object. (car jack) Copy this

 increasing the distance over which the force can be applied. (ramp) Copy this

 by changing the direction of the applied force. (opening the blinds) Copy this

 increasing the speed in which the work is done. Copy this

Six Simple Machines  The six simple machines are: Lever Lever Wheel and Axle Wheel and Axle Pulley Pulley Inclined Plane Inclined Plane Wedge Wedge Screw Screw Copy this

Forces involved:  Input Force FIFIFIFI  Force applied to a machine  Output Force FOFO  Force applied by a machine Copy this

Two forces, thus two types of work  Work  Work Input work work done on on a machine =Input force x the distance through which that force acts (input distance)  Work Output Work done by a machine =Output force x the distance through which the resistance moves (output distance) Copy this

Can you get more work out than you put in?  Work output can never be greater than work input.

Ideal machine W in = W out 100% energy transfer. 100% energy transfer. There is no such thing as an ideal machine – you always lose some energy (through friction, air resistance, etc.) Copy this

Efficiency – a measure of how much of the work put into a machine is changed into useful output work by the machine. (less heat from friction) Copy this

efficiency = efficiency = (W out / W in ) x 100% (W out / W in ) x 100% W in is always W in is always greater than W out greater than W out Copy this

Mechanical Advantage How much a machine multiplies force or distance How much a machine multiplies force or distance output force (F R ) output force (F R ) MA = input force (F E ) MA = input force (F E )Or input distance output distance Copy this

The Lever The Lever  A bar that is free to pivot, or move about a fixed point when an input force is applied.  Fulcrum = the pivot point of a lever.  There are three classes of levers based on the positioning of the effort force, resistance force, and fulcrum. Copy this

Lever MA = Length of effort arm Length of resistance arm Length of resistance arm Remember that Length is the same as distance or input distance output distance Copy this

INPUT FORCE (EFFORT FORCE) OUTPUT FORCE (Resistance Force) INPUT ARM (EFFORT DISTANCE) OUTPUT ARM (RESISTANCE DISTANCE) FULCRUM

Inclined Planes  Imagine how hard it would be to walk up the side of a steep hill.  It would be MUCH easier to follow a gentle slope of a winding trail….why is this? What is happening to input distance if you decide to take the curvy trail instead of going straight up the hill? Because input distance is greater than output distance, in this case, the input force is decreased…..so it’s easier for you! Copy this

Inclined Plane MA = effort distance effort distance Resistance distance Resistance distanceor input distance output distance Copy this

Inclined Planes  Inclined plane: a slanted surface along which a force moves an object to a different elevation Input distance Output distance Copy this

Inclined Planes  What is the MA of the following inclined plane? 6m 1 m Mechanical Advantage = 6 MA for inclined plane will NEVER be less than 1

Wedges  Similar to inclined planes BUT sloping surfaces can move.  Wedge: a V-shaped object whose sides are two inclined planes sloped toward each other. Examples: knife, axe, razor blade Copy this

The Screw The Screw  An inclined plane wrapped around a cylinder.  The closer the threads, the greater the mechanical advantage  Examples: bolts, augers, drill bits Copy this

The Pulley The Pulley  A chain, belt, or rope wrapped around a wheel.  Can either change the direction or the amount of effort force  Ex. Flag pole, blinds, stage curtain Copy this

Pulley The MA of a pulley or pulley system is equal to the number of pulleys supporting the load being lifted. The MA of a pulley or pulley system is equal to the number of pulleys supporting the load being lifted. A single fixed pulley only changes the direction so MA = 1 A single fixed pulley only changes the direction so MA = 1 Copy this

MA = Count # of pulleys in a row Fe

Wheel & Axle  Consists of 2 discs or cylinders, each one with a different radius. wheel axle Copy this

 A combination of two or more simple machines.  Cannot get more work out of a compound machine than is put in. Copy this

Rube Goldberg Machines Rube Goldberg machines are examples of complex machines. All complex machines are made up of combinations of simple machines. Rube Goldberg machines are usually a complicated combination of simple machines. By studying the components of Rube Goldberg machines, we learn more about simple machines

When you slip on ice, your foot kicks paddle (A), lowering finger (B), snapping turtle (C) extends neck to bite finger, opening ice tongs (D) and dropping pillow (E), thus allowing you to fall on something soft. Safety Device for Walking on Icy Pavements