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Simple Machines- Year 8 Science

Diagnostic test, work, simple machine types, classes, force/speed multipliers, mechanical adv.
by

Cass Comyns

on 1 November 2012

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Transcript of Simple Machines- Year 8 Science

Don't think cranes... How simple are we talking? Don't think robots... Not printers... Not laptops or computers... Not fridges or ovens... Not cars... Not trains or buses... or iPods! Think more simple... Refresh your knowledge of forces... A 'force' is any influence that causes an object to undergo change... What does a force DO? A force may push, prod, poke, pull, stretch, spin, rotate, slide, shoot, slow down, speed up, drag... do many kinds of things to an object! In general, there are 4 main things a force can DO to an object... A force may make an object STOP or SLOW DOWN A force may make an object START or SPEED UP A force may change an objects SHAPE A force may change an objects DIRECTION Forces are not always BALANCED... There are 6 main types of forces....! Non contact Forces Contact Forces Mechanical Force (cc) photo by theaucitron on Flickr (cc) photo by theaucitron on Flickr Friction Buoyancy Gravity Static Electricity Magnetism Drawing Force Diagrams Arrows are used to indicate the force Does force always result in movement? Get into pairs...
One person should do the action
Observe if the object moves. If it does move, estimate the distance Person 1. stretch a rubber band open using two hands. Hold it open!!! Person 1: stand with your back against the wall
Person 2: use your hands an (gently) push on your partners shoulders.
Observe; does Person 1 move a distance? Person 1- Push against a work bench (not a table)
Person 2. Observe...does the table move a distance? Person 1; now push against a table...
Person 2; observe. Does the table move a distance? HOLD IT!!!!!!!!!! Release.
Discuss with your partner what you could do to hold a rubber band open WITHOUT using your own body Would your suggestion make the task easier for us? When a force is applied, if there is a change in DISTANCE, then WORK is done. Work Work = (effort force) x (distance)
W = Fd Simple Machines help make our lives easier... We know that WORK equals force multiplied by distance...
Therefore WORK only happens when there has been a change in distance Quick Quiz!!! A teacher applies a force to a wall and becomes tired. Work? A book falls off a table and freefalls to the ground. Work? A rocket accelerates through space. Work? A pokemon ball is thrown at Schmarizard (I made that up). Work? Increase the DISTANCE so the effort force needed is LESS! There are 5 types of Simple Machines we will be looking at... Wheels/axles Levers Gears Pulleys Ramp or Inclined Plane (cc) image by nuonsolarteam on Flickr Simple Machines... On your computer... Write this in your workbook-
Join group tqrc8x on Edmono
Find the link to Ed heads...
Find the link to the Ed heads PowerPoint
Save the PowerPoint to your drive
Open the PowerPoint and follow the instructions Simple Machines have different effects FORCE MULTIPLIER: Devices that REDUCE the FORCE needed to travel. ***Advantage***: lifting heavy objects or doing other things that require large amounts of force They may decrease FORCE needed to move the object... ...Or they they may increase the speed or distance the object travels They do this by INCREASING the DISTANCE traveled. SPEED MULTIPLIER: -Devices that INCREASE the SPEED or DISTANCE traveled. - Need a LOT of effort force! ***Advantage***: the load moves over a greater distance or at a higher speed. If there is a change in DISTANCE when FORCE is applied, then WORK is done. Work Work =
(effort force) x (distance)
W = Fd Remember... A teacher applies a force to a wall and becomes tired. Work? A book falls off a table and freefalls to the ground. Work? A rocket accelerates through space. Work? A pokemon ball is thrown at Schmarizard (I made that up). Work? Test your understanding! (Remember this guy?) Ramps/ Inclined Planes... ...they were used to build the pyramids! Used when we need to get a heavy object up to a higher level. To do WORK, we have to move an object a distance... **Imagine** carrying a heavy box onto a platform... To get the box on the platform we could hold the box and JUMP! Lots of effort Short distance Or... we could use a step? Or a ramp? When we do this... We increase the distance... BUT THE EFFORT FORCE IS smaller... Inclined Planes.... One type of ramp is ... a WEDGE - An inclined plane that moves through another object, splitting the object as it moves through. EXAMPLES: Another type of ramp is ... A SCREW - Screw is also like a ramp ... it spirals around a metal cylinder
- A MASSIVE distance is covered... very little force is required... but lots of turning... Distance is INCREASED...
Force is DECREASED..
Work remains the SAME. Wheel/Axles... We need to know what a FULCRUM is... What would you call this? The support on which a lever PIVOTS... Who is stronger? ARM WRESTLE! Pair up!
Arm wrestle!
Think about who is winning. How can you prove this? How can you measure this... what UNIT do you use?
mm? mL? L? g? cm? kG? Force is measured using a SPRING BALANCE.
The unit force is measured in is NEWTONS (N). (Like a RULER measuring distance in CENTIMETRES) Levers... Remember... Mechanical Advantage Calculate the mechanical advantage of... A LEVER is any stiff rod made to turn around a FULCRUM (or a pivot)
The LOAD is placed somewhere along the rod... The effort FORCE is applied and causes movement. The fulcrum can be placed at different spots along the rod. This gives us 3 different types of levers Look around the room. How many levers can you spot? In a FIRST ORDER LEVER, the load is at one end, the effort force is at the other, and the fulcrum is in the middle. FLE 123 In a SECOND ORDER LEVER, the effort force is at one end, the fulcrum is at the other, and the LOAD is in the middle. FLE 123 In a THIRD ORDER LEVER, the load is at one end, the fulcrum is at the other, and the effort force is in the middle. FLE 123 Measures how much easier a simple machine makes a task. Calculated by dividing the LOAD by the EFFORT FORCE 1) The load is 12N and the effort force is 6N
2) The load is 18N and the effort force is 6N
3) The effort force is 3N and the load is 18N
4) The load is 5kg (about 50N weight force) and the effort is 10N

Which of the 4 above would be
the best machine? Extension activity (when you are done with your worksheet): look at your pictures. Which class of levers always MULTIPLIES force? And which always multiplies SPEED? I know of a tool that you're going to like,
If you skate on a board or pedal your bike,
Using it turns heavy loads into light,
It's a well-rounded worker, a handy device,
Tell me the name of this machine,
The one that moves weight so easily?
It's a ____________ and ___________ A Simple Machine made of two parts:
The AXLE is a small wheel, attached to a larger WHEEL.
These two parts must move together to be classified as a simple machine. Wheel/Axle as a FORCE MULTIPLIER If a small force is applied to the rim of the wheel, to make it move a great distance...
It is transformed into a large force at the axle, to move a smaller distance What is a force multiplier? How may a wheel/axle be a FORCE multiplier? Wheel/Axle as a SPEED MULTIPLIER If a large force is applied to the rim of the axle, to make it move a small distance...
The wheel will move very quickly, covering a great distance with less force. What is a speed multiplier? How may a wheel/axle be a SPEED multiplier? Gears... When one more than one pair of gears are used together. How... Can you use one wheel to move or turn another? A wheel with identical TEETH around it's edge.
When two gears are interlocked, if one spins, so will the other.
Gears can be used to change the speed, spinning force, or the direction of rotation. If the AXLE is turning the gear... this gear is called the DRIVING GEAR.
If the teeth of another gear (the 'follower') mesh with the driving gear it will also turn! If gears are identical in size they move at the same speed, in different directions. Identical sized Gears... If the driving gear is the largest... The smaller gear will rotate faster. This is called 'gearing up' If the driving gear is the smallest... The larger gear will rotate slower. This is called 'gearing down' Compound Gear Train: Pulleys A PULLEY is a grooved wheel that turns on an axle. A system of pulleys is called a block and tackle 1) 2
2) 3
3) 6
4) 5 Types of Pulleys...
There are 3! A SINGLE FIXED PULLEY Changes the direction of the force. Mechanical Advantage (MA) = 1 A SINGLE MOVEABLE PULLEY Moves in the same direction as the force and multiplies the force by 2. Mechanical Advantage (MA) = 2 A BLOCK & TACKLE Changes the direction of the force and multiplies the force MANY times. Mechanical Advantage (MA) = number of strands (except the one being pulled.) A pulley may... 1. Change the direction of the effort force.
2. Multiply the effort force.
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