Simple Machines

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Simple Machines Preparation Grade Level: 3-8 Group Size: 25-30 Time: 50 Minutes Presenters: 3-4 This lesson has extension activities. Select the most appropriate version depending upon the curriculum objectives. Objectives This lesson will enable students to: Describe and define simple machines. Identify simple machines in their world. Define and experience the definition of work. Identify a pulley, lever, gear, wheel and axle. Explain how pulleys, levers, gears, wheels and axles work to give us greater power. Standards This lesson aligns with the following National Science Content Standards: Unifying Concepts and Processes in Science, K-12, 5-8 Physical Science, K-4, 5-8 Science and Technology, K-4, 5-8 Note: While we strive to make the lessons as safe as possible, there are risks inherent in using certain equipment or materials. Safety guidelines have been published where necessary within each lesson. Please ensure you have adequately reviewed the lesson and have the information and materials necessary to perform it safely. Micron is not liable for any injuries that result from use of these lessons. Some of the equipment used in the Machines lesson can pose a safety hazard if used incorrectly. Follow all safety guidelines and instructions as noted within the text of the lesson to avoid potential injury. Materials Introduction “Machines” PowerPoint - http://www.micron.com/k12/resources.aspx Overhead projector and screen Car jack Class set of pencils and rulers – optional Revision Date: 8/27/2007 1 © 2000 Micron Technology Foundation, Inc. All Rights Reserved

Transcript of Simple Machines

Simple MachinesPreparationGrade Level: 3-8 Time: 50 Minutes Group Size: 25-30 Presenters: 3-4

This lesson has extension activities. Select the most appropriate version depending upon the curriculum objectives.

Objectives

This lesson will enable students to:

Describe and define simple machines.

Identify simple machines in their world.

Define and experience the definition of work. Identify a pulley, lever, gear, wheel and axle. Explain how pulleys, levers, gears, wheels and axles work to give us greater power.

Standards

This lesson aligns with the following National Science Content Standards: Physical Science, K-4, 5-8

Unifying Concepts and Processes in Science, K-12, 5-8 Science and Technology, K-4, 5-8

Note: While we strive to make the lessons as safe as possible, there are risks inherent in using certain equipment or materials. Safety guidelines have been published where necessary within each lesson. Please ensure you have adequately reviewed the lesson and have the information use of these lessons. Some of the equipment used in the Machines lesson can pose a safety of the lesson to avoid potential injury. and materials necessary to perform it safely. Micron is not liable for any injuries that result from hazard if used incorrectly. Follow all safety guidelines and instructions as noted within the text

Materials

Introduction

Machines PowerPoint - http://www.micron.com/k12/resources.aspx Overhead projector and screen Car jack

Class set of pencils and rulers optional

Revision Date: 8/27/2007

2000 Micron Technology Foundation, Inc. All Rights Reserved

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Lever Station

Arm/rod

Fulcrum/pivot

20 lbs of weight

Lever poster Appendix A

Pulley Station

Fixed pulley

Additional pulleys Rope

6- 8 A frame ladder request from school Scale

20 lbs of weight

Pulley poster Appendix B

Gear, Wheel, and Axle Station Bike with gears Bike stand or trainer

Gears posters Appendix C

Wheel and Axel poster Appendix D Chalk, masking tape, or rubber band

PreparationSet up the stations for the activities with the equipment needed.Lever Center the arm/rod on the fulcrum. Tie the two weight plates flush around the bolt on the end of the arm/rod. Place the poster against the fulcrum for the introduction. Pulley - Ask the teacher for the A frame ladder.

Straddle the fixed pulley across the folding hinges of the ladder. Place the weight plates and semi-circle around them during the introduction. Gears, wheel, and axle Mount the bike on the stand on top of a table. Put a piece of masking tape or chalk mark stand in a semi-circle around them. around the back tire as a rotation marker. Place posters in an area that students can sit or

rope on the floor beneath the fixed pulley. Position the posters where the students can form a

Caution: If bike is set up on a table, make sure the table is stable, level, and wide

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enough to hold the entire stand and bike. Failure to do so could cause the bicycle to

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fall and possible injuries.

Lever and gear - optional station

Ask the teacher to divide the class in the appropriate number of groups. The students will rotate through each of the stations at the end of the introduction.

Place the car jack in an area of the room where four to eight students can gather.

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IntroductionHave all of the volunteers introduce themselves and give a brief description of their jobs. Use the Machines PowerPoint slides for the introduction. Slides are available athttp://www.micron.com/k12/resources.aspx .

We are here to have fun with simple machines and learn how they work, how we use them, the different types, the importance of simple machines, and what work is.

Display only the title of the What is a Machine? slide. Cover the remainder of the overhead with a piece of paper.Q: What is a machine?

A: A system or device which uses energy to perform a task. A system that will help you do work.

Q: What is a simple machine?

A: A machine with few or no moving parts.

Display only the title of the Types of Simple Machines slide. Cover the remainder of the overhead with a piece of paper.Q: What types of simple machines can you name?

A: Levers, pulleys, gears, wheel and axle, inclined plane, screw, and wedge. There are seven main simple machines that are combined to form complex machines. Complex machines combine two or more simple machines to perform a task, or do work.

Show the slide of the crane and ask students to identify the simple machines that have been combined to make this complex machine: wheel, axle, gears, and levers.Today we are going to focus on four of the seven simple machines: levers, pulleys, gears, wheel and axle. Before we divide into small groups to conduct hands-on experiments using simple machines to do work, we need to define what work is.

Show the title of the What is Work slide.Q: What is work?

A: Answers will vary. W= F X D

Work is a force applied through a distance.

Work = Force multiplied by the Distance

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Simple machines make work easier by decreasing the amount of force needed at the expense of greater distance.

Work Demonstration Activities

There are two activities to illustrate the work equation. Select the most appropriate activity.Option one Pencil, Ruler and Book: W= F X D

To make more sense of this definition we are going to use a ruler, a pencil, and a text book. Work (lifting the weight) = Force (how hard you had to push down on the ruler) multiplied by the Distance (how far down you push the ruler).

Place the book on a flat surface with the binding facing your left hand. Slide the ruler under the edge of the book binding up to the half inch mark. Position the pencil under the ruler at the six inch mark. Press down on the twelve inch mark of the ruler until the book is completely lifted. Do this once again and observe the distance between the table and the twelve inch marker on the ruler.

Move the pencil to the four inch marker on the ruler and use your little finger to lift the book. Q: What difference did you notice in the amount of force necessary to lift the book? A: It was a bit less.

Q: What has happened to the distance between the table and the ruler since we moved the pencil to the four inch marker? A: The distance doubled.

Finally, move the pencil to the two inch marker on the ruler and use your little finger to lift the book.

Q: What difference did you notice in the amount of force necessary to lift the book? A: It got even easier and took a lot less force.

Q: What has happened to the distance between the table and the ruler since we moved the pencil to the two inch marker? A: Again, the distance doubled. The lever made it much easier to lift the book, as the distance increased the amount of force

needed decreased. This is an example of how we use multiplication in our every day activities.

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Option Two Car Jack:

Note: Ask the teacher or adult volunteer in advance to review to the following safety participating.

information regarding the car jack demonstration and ask if he or she is comfortable

Important: To insure adequate safety, you will need four volunteers for this activity.

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Two volunteers standing on each side of the individual being lifted to allow the volunteer to remain steady while the fourth volunteer operates the car jack.

Q: How many of you think you can lift your teacher 10 off the ground? A: Answers will vary.

Facilitate having a student attempt to lift the teacher/volunteer without any assistance from a machine.Q: What simple machine could we use that would allow us to complete the job? A: Answers will vary. We could use a lever.

I have an example of a lever that is frequently used to lift heavy, bulky, or awkward items short distances a car jack.

Have the teacher stand on the plate on the car jack and allow the student to operate the jack to lift the teacher. Ask two students to stand alongside the teacher to help steady the teacher. Using the car jack talk about how the force needed to lift the teacher is minimized, but how the distance that you were required to move to get the jack up is great. For example: the distance and number of times you are required to move the jack handle up and down.Q: How did the force needed change when you used the car jack? machine.

A: The force was much less than when you tried lifting the teacher/volunteer without a

Q: How was the distance that you moved impacted? A: When using the car jack the distance was much greater because you had to pump the handle multiple times.

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Activity Stations and SafetyUse the Activity Stations and Safety slide to introduce the stations.Now we are going to work! Each of you will have an opportunity to use all of the simple

machines set up around the room. When you start each station, gather around the poster(s) and listen closely to the volunteer who will give you an introduction to the activity. It is very safety first to ensure team members are not injured. We want to do the same today. Here are a few safety guidelines that you need to follow: Listen to instructions carefully. Wait your turn. Keep your hands to your sides. Do only what you are instructed to do. important to be safe when using simple machines. At Micron when working, we always put

You will be going to the different stations:

At the lever station we will investigate how weight can be lifted with very little effort. At the pulley station we will learn about how pulleys are used in machines where direction of movement must be changed.

At the gear, wheel, and axel station with the bicycle we will talk about your bicycle as a machine and the gears, wheel, and axle it has. items. At the car jack station you will see how simple machines are used to lift large or bulky

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Lever Station

Prop the Lever poster Appendix A against the fulcrum. Have students form a semi-circle around the poster.Q: What is a lever used for? cut or open objects.

A: A lever is a simple machine used to lift objects and can be modified so that it can be used to

A lever is made up of four parts: rod (sometimes called an arm), fulcrum (or pivot), load, and effort.

Q: Which part of our lever is the load?

A: The weight plates (object being lifted). Q: Which is the arm? A: The long 2X4

Q: Which is the fulcrum?

A: The pivot support in the center. The fulcrum is sometimes called the pivot. It can be described as a fixed point upon which the arm or rod will pivot. Some fulcrums are stationary and others can be moved. Seesaws have stationary fulcrums.

Q: What was the fulcrum in our experiment with the book? A: It was a pencil.

Q: Was it fixed or moveable? A: Moveable

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The fulcrum that we are going to use to lift the weight is moveable. Q: Where is the effort?

A: Point of force applied to move the load. Pay close attention as we lift the weight to the change in force and distance when we move the fulcrum during our experiment.

Have students line up on one side of the lever. The fulcrum should be in the center of the arm, equal distance between the load and the effort. Demonstrate how to apply force to the arm, how to move the weight slowly up and then down, and where to stand to avoid being bumped with the end of the lever arm when lowering the weights. Instruct the students to participate one at a time, and to return to the line when finished.Caution: The load must be lowered slowly to avoid possible injury from the weights

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or the lever arm. Have the students return to the line to avoid injury when the next student is participating

After each student has a turn, ask the following question.Q: How do you think the effort will change when we move the fulcrum closer to the load?

Encourage all responses. Allow time for students to respond. Let them test their predictions. Move the arm on the fulcrum. Have each student take a turn at lifting the load.A: It will change the amount of effort required.

Q: Was the work you did this time different than before?

A: Yes, the force required to lift the load was less, but the distance that arm moved was greater.

Continue to move the arm on the fulcrum closer to the load one notch at a time allowing each student to experience how the effort/force required changes. Each time you move the arm draw the students attention to how the force decreases and the distance that the arm increases. Evaluate the amount of time left before rotation. Brainstorm with the students examples of levers: hinges, seesaw, hammer, bottle opener, fork, nutcracker, crowbar, fishing rod, wheelbarrow, wrench, stapler, scissors, and shovel. Time permitting discuss the difference between first, second, and third level levers.The position of the fulcrum determines the class of the lever and how much effort is required to move the object.

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First Class

One end will lift an object up just as far as the other end is pushed down. The fulcrum is in the middle. Examples include scissors and a seesaw. Seesaw: The load is the person who goes up, and the effort applied is the weight of the person who goes down. The rod is the board that you sit on and the fulcrum is the center pivot.

Second Class

The load is nearer to the fulcrum. The effort needed to lift the load is less than that of a first class lever. Examples include a bottle cap opener and a wheelbarrow. load is between them. Wheelbarrow: The axle of the wheel is the fulcrum, the handles take the effort, and the

Third Class

The effort is in the center. Regardless of the distance the load is from the fulcrum, the effort used to lift the load has to be greater than the load. Examples include a stapler, hockey stick, broom, and a fishing pole.

Fishing pole-the load is the fish; the handle end is the fulcrum. When the pole is given a tug, one end stays still but the other end flips in the air catching the fish.

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Pulley Station

Prop the poster against the wall or ladder. Have students sit or stand in a semi-circle around the poster. Introduce the concepts of fixed, moveable, and combined pulley systems. Explain that we will be experimenting with both fixed and combined pulleys. Explain to the students that it is important to pull up or down on the rope in direct alignment with the direction of the pulley. To ensure that the ladder does not tip, have a volunteer or the teacher stand on the bottom rung of the ladder. Do not allow students to climb the ladder. Demonstrate how to lower the weight using the hand-over-hand technique, and instruct the students not to allow the weight to swing during the activity. Insure that students position themselves so that they could not be injured by the weights.Caution: Pulling the rope from the side may cause the ladder to tip, especially if the

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ladder is not properly secured. Lowering the weights improperly could cause slight injury to the student or the floor.

injury from the pulleys or the rope. Allowing the weights to fall rapidly could cause

Single pulleys are used in machines where the direction of movement must be changed. An

example is an elevator, where the upward movement of the elevator is linked to the downward movement of a counterweight. This change of direction can be arranged with a wheel and a rope. The wheel is fixed to a support, and the rope is run over the wheel to the load. A pull downward on the rope can lift the load as high as the support. The load moves the same distance as the rope is pulled.

Show the students the black bag of weight.

Q: How much weight do you think is in the bag? Use your knowledge of size to guess.

Encourage each student to make a prediction.A: 20 lbs

Show the students the two ten pound plates in the bag.

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Tie or clip one end of the rope to the bag of weight and thread the other end of the rope through the pulley attached to the board. The pulley board is straddling folding hinges of the ladder. This is a fixed pulley.Q: What type of pulley have we created?

Encourage students to look back at the poster to find the answer.

A: We have created a fixed pulley. One pulley attached to a stable arm. Q: Do you think that the force required to lift the bag will be less than, equal to, or more than the twenty pounds of weight in the bag? A: Slightly more force.

Encourage each student to make a prediction.

Make a slip knot in the rope. Loop the scale through the knot hole. Have the student pull downward using the handle on the scale. Look at the dial and identify how many pounds of force are needed to lift the bag.Q: What do you think will happen to the amount of force needed to lift the bag if we add another pulley? A: It will get easier.

Thread the rope through the pulley on the bag. The rope will be pulled in an upward direction with two pulleys (opposite the direction you were pulling with the fixed pulley only). Use the scale again to pull on the rope in an upward direction lifting the weighted bag.Q: Did it take more force or less force than when we had one fixed pulley? A: Using a combined pulley (two pulleys) we used less force. Q: How many pounds of force did the scale read? A: Ten pounds

Q: By how much did the amount of force required change?

A: The amount of force needed to do the same amount of work was cut in half.

Point out to students that the distance that the rope had to travel through the two pulleys increased significantly. This will help to reinforce that the force required decreases at the expense of the distance.We started out having to apply 20+ pounds of force to lift the bag with one pulley. When we used two pulleys the amount of force needed dropped by half to ten pounds.

Q: How much force do you think will be required to lift the bag if we add a third pulley? 12

A: Five pounds of force will be needed. Lets test your prediction.

Thread the rope through the second pulley on the cross-board. The rope will be pulled in a downward direction with three pulleys. Use the scale again to pull on the rope to lifting the weight bag.Q: Was our prediction correct? A: Yes

Refer back to the poster. Summarize and reinforce:

Fixed pulley -- one pulley attached to a stable arm.

Requires more force to lift the load than the load itself.

The single pulley changes the direction of the lifting force. You can pull down on the needed as would be without a pulley, but it feels less because you are pulling down.

rope to lift the object rather than lifting up or pushing up. The same amount of effort is

Moveable pulley

The pulley moves with the load.

Allows the effort to be less than the weight of the load.

Combination pulley - combination of a fixed and moveable pulley pulley.

When you add the second and third pulley at the pulley station you create a combined The amount of effort required is half the load.

Brainstorm with the students examples of pulleys: flag pole, mini-blinds, elevator, winch, wishing well, crane, window washing platform, sail rigging on a sailboat, swing at the Discovery Center.

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Gears, Wheel, and Axle Station

Form a semi-circle around the mounted bike. Gather students around the bike posters. Instruct students about the importance of keeping away from the gear cam and spokes to avoid getting their fingers, hair, clothing, jewelry, etc. caught. Position the students so they are away from the bicycle when they are not the active participant to avoid injury. Ensure the active participant moves the pedals only when instructed.Caution: The bike spokes and gear cam present a potentially serious pinch point. Stress the importance of staying clear of these points, whether moving or not.

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Failure to keep clear of these could result in serious injury. Also refer to the Caution statement on page 2 regarding the proper set-up of the gear station.

Q: Did you know that your bicycle is a machine?

A: The chain connecting the pedals of your bicycle to the rear wheel acts as a belt to make the that is larger than the driven gear, attached to the rear wheel.

wheel turn faster than your feet. The chain goes around a drive gear--attached to the pedals--

On a bicycle with more than one gear, as in a "three-speed," "ten-speed" or "18-speed" bicycle, the different sizes of gears make it easier to go up and down hills. The gears also let you change the distance that the bike moves forward with each pedal stroke. Lets experience this. Q: What three simple machines are combined to make a bike? A: Gears, wheel, and axle.

Use the Gear posters Appendix C to illustrate the following questions.Q: What is the gear setting that will require less force to pedal on a flat road or downhill? high speed.

A: The rear wheel gear (driven gear) needs to be smaller than the front gear (chain wheels) for

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Rotate students through holding onto the pedal and turning the pedal one full rotation and have the group count the number of times the back wheel turns. SAFETY: Reinforce the importance of keeping hands away from the gear cam and spokes. Also have the students move back from the student turning the pedal.NOTE: Position the back wheel so the marker is centered at the top. This will make it easier to around the wheel.

count the wheel rotations. The marker can be the valve stem, a piece of tape, or a rubber band

Q: What is the setting that will require less force to pedal uphill so that the driven gear (rear wheel) turns with less speed, but more force? A: The rear gear (driven gear) needs to be bigger than the front gear (chain wheels). A small motion of the pedal will give us a large motion of the wheel.

Rotate students through holding onto the pedal and turning the pedal (use hand) one full rotation. Have the group count the number of times the back wheel turns. Compare the number of wheel rotations to the earlier gear setting. Discuss how the work changes as the gears manipulate the force applied and distance that the bike would move forward. Brainstorm with the students examples of gears: clock, automobile, drill, motorcycle, and bicycle. Brainstorm with the students examples of wheels and axle: pencil sharpener, rolling pin, windmill, roller blades, and dishwasher rack rollers, bike wheel, car wheel, wagon wheel, door knob, and skateboard.

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Additional Lever Station Car JackQ: What simple machines are combined in a car jack? A: Lever and gears.

You saw the demonstration with the car jack in the the jack out.

introduction. Now all of you will have the opportunity to try

Important: To insure adequate safety, you will

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need four volunteers for this activity. Two

lifted so that he or she can steady themselves while the fourth volunteer operates the car jack.

volunteers stand alongside the individual being

Position one student squarely on the metal plate, using the other students for balance. Demonstrate to another student how to operate the car jack. Have the students take turns with the tasks. Using the car jack talk about how the force needed to lift the teacher is minimized, but how the distance that you were required to move to get the jack up is great. For example, the distance and number of times you are required to move the jack handle up and down.Q: How did the force needed change when you used the car jack? machine.

A: The force was much less than when you tried lifting the teacher/volunteer without a

Q: How was the distance that you moved impacted? multiple times.

A: When using the car jack the distance was much greater because you had to pump the handle

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ConclusionUse the Machines presentation for the review questions.Q: Simple machines make work easier. A: True

We can call this the mechanical advantage. Using simple machines we use less force at the expense of distance to make work easier.

Are you ready for a challenge? Lets see what you have learned.

Levers

Casey and Kelly both work at Micron. It is their job to move 100 lbs of memory devices into a testing machine for 12 hours a day. Each has a lever to help them do the lifting. Q: Who will be less tired at the end of the day? A: Kelly

Q: Why is it easier for Kelly? the load is decreased.

A: It is easier for Kelly because the fulcrum is closer to the load, thus the effort required to lift

Q: What makes up a lever?

A: Fulcrum, rod, load, and effort

Review examples of levers.

Pulleys100 lbs.

Sammy and Robin both work at Micron washing windows. Their window washing supplies weigh

Q: Which team member is going to have to use more muscle and apply more force to do the same amount of work? A: Sammy

Q: How much harder does Sammy have to work?

A: Sammy has to work twice as hard when washing windows because he has to lift 100 lbs of pulley system with two pulleys.

supplies all day and Robin only has to lift 50 lbs of supplies because she is using a combined

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Q: What is a pulley?

A: A grooved wheel that turns around an axle with a rope passing through it. Q: How many types of pulleys are there? A: Three Fixed

Moveable

Combination (Refer to the slide of Sammy & Robin: Sammy has a fixed pulley and Robin has a combined pulley.)

Review examples of pulleys.

Gears

Pat and Logan are both pedaling on a flat surface. Q: Who will use more force? A: Pat

Q: Why is less force required by Logan?

A: Logan is in a higher gear. The larger gear in back and the smaller gear in front will allow her to go a greater distance with less effort. Q: What is a gear?

A: Toothed or pegged wheels that mesh together Q: If a gear with 10 teeth and another with five teeth turns, after the big gear turns once around, the small gear will turn _______ rounds. A: Two

Q: Which part of the wheel and axle is the fulcrum? A: Axle

Review examples of gears, axle, and wheel. Pass out pencils and parts to the students.

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Machines ExtensionGearsGears are measured by counting the number of teeth they have. When used with an axle, gears are an example of the simple machine called the wheel and axle. Gears can mesh together in many different ways to transfer motion and increase or decrease force, torque, and speed, or change direction. Mechanical Advantage (MA) = number of teeth on rear gear

number of teeth on front gear

Determine the Mechanical Advantage of the gear ratios shown. Front Gear 32 teeth 32 teeth 32 teeth Rear Gear 12 teeth 18 teeth 30 teeth MA

1. What is the MA of the smaller rear gear to the front gear? 2. What is the MA of the largest rear gear to the front gear? 3. What gear selection offers the greatest mechanical advantage and why?

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LEVER

Fresistance Lresist Lapplied

Fapplied

Fulcrum Fr Resistance FORCE or the weight of the load being lifted. Fa Applied FORCE or the force being applied to lift the load. Lr Resistance LEVER ARM length from resistance force to fulcrum. La Applied LEVER ARM length from the applied force to the fulcrum. Fulcrum Point of support or pivot point of a lever. Equilibrium The point where the opposing forces (moments) are balanced. MA Mechanical Advantage is the degree by which the applied force is multiplied. Step 1: Calculate the applied force (Fa) required to lift a 30 lb load (Fr) at the following

resistance lever arm intervals: 4ft, 2ft, 1ft. The total length of the lever is 8ft, so we need to calculate the applied lever arm first. Fill in the values La and Fa in the worksheet below. Equilibrium equation: Fa x La = Fr x Lr So, Fa = Fr x (Lr / La)

Step 2: Calculate the mechanical advantage (MA) at each of the resistance lever arm (Lr) intervals. Fill in the MA values in the worksheet below. Mechanical Advantage equation:

Fa x MA = Fr

So, MA = Fa / Fr

Step 3: Test out the answers on the demonstration lever. Resistance Force (Fr) 30 lbs 30 lbs 30 lbs Resistance lever arm (Lr) 4 ft 2 ft 1 ft Applied lever arm (La)8 ft - (4 ft) = 4 ft

Applied

Force (Fa)30 x (4/4)=30

Mechanical

Advantage (MA) 30 / 30 = 1

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Lever Questions: 1. Do the calculated applied forces from the worksheet exactly match the actual tested applied forces determined in the demonstration? Why or Why not?

2. Why is the mechanical advantage of a lever so useful?

3. What do we give up (or tradeoff) for the benefits of mechanical advantage?

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PULLEY

Pf

Pf

Feffort Fresist

Feffort

Pf

Pm

Pf

Fresist

Pf Fixed PULLEY - attached to something that does NOT move i.e. a wall or ladder.

They are used only to change rope direction and/or location of load or effort force.

Pm Moveable PULLEY - capable of movement and used in conjunction w/ a fixed pulley. They are used to create mechanical advantage. Fr Resistance FORCE or the weight of the load being lifted. Fe Effort FORCE or the force being applied to lift the load. Equilibrium The point where the opposing forces are balanced. MA Mechanical Advantage is the degree by which the effort force is multiplied. Step 1: On the two fixed pulley setup, measure the effort force (Fe) required to lift a 20 lb resistance load (Fr). Record results in the table below.

Step 2: Add the moveable pulley and repeat step one.

Record results in the table below.

Step 3: Calculate the actual mechanical advantage using the equation below and record results in the table. Pulley Mechanical Advantage equation: Fe x MA = Fr So, MA = Fr / Fe

Tip

The ideal mechanical advantage of a pulley system can also be found by counting every rope supplying an upward force on the resistance.

# of pulleys Two fixed Two fixed + one moveable

Resistance Force (Fr) 20 lbs 20 lbs

Effort Force (Fe)

Mechanical Advantage (MA)

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Questions1. Is there an advantage to using two fixed pulleys vs. a single fixed pulley? Explain.

2. What happened when we added the moveable pulley?

3. What do we give up (or tradeoff) for the benefits of mechanical advantage?

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Gears Answer KeyMechanical Advantage (MA) = number of teeth on rear gear number of teeth on front gear Front Gear 32 teeth 32 teeth 32 teeth Rear Gear 12 teeth 18 teeth 30 teeth MA 0.4 0.6 0.9

1. What is the MA of the smaller rear gear to the front gear? 0.4

2. What is the MA of the largest rear gear to the front gear? 0.9

3. What gear selection offers the greatest mechanical advantage and why? The smaller rear gear (0.4) because you are applying less force.

LEVER Answer Key

Resistance Force (Fr) 30 lbs 30 lbs 30 lbs

Resistance lever arm (Lr) 4 ft 2 ft 1 ft

Applied

lever

Applied Force (Fa) 30 x (4/4)=30 30 X (2/6)=10 30 X (1/7)=4.3

Mechanical Advantage (MA) 30/30 = 1 30/10 = 3 30/4.3 = 7

arm (La) 8 ft - (4 ft) = 4 ft 8 ft (2 ft) = 6 ft 8 ft (1 ft) = 7 ft

1. Do the calculated applied forces from the worksheet exactly match the actual tested applied forces determined in the demonstration? Why or Why not? the friction variable. No, because the resistance lever arm distances may not be exactly the same and you have

2. Why is the mechanical advantage of a lever so useful?

It enables the user to lift more than would be possible unassisted.

3. What do we give up (or tradeoff) for the benefits of mechanical advantage?

A greater mechanical advantage decreases the total distance that the load is lifted.

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Pulleys - Answer Key# of pulleys Two fixed Two fixed + one moveable Resistance Force (Fr) 20 lbs 20 lbs Effort Force (Fe)20

Mechanical Advantage (MA) 20/20 = 1 = no advantage 20/6.66 = 3

1/3 = 6.66

1. Is there an advantage to using two fixed pulleys vs. a single fixed pulley? Explain. No. The effort force is equal to the resistance force. 2. What happened when we added the moveable pulley? The ropes and the pulley start supporting the weight thus the perceived amount of resistance force is less.

3. What do we give up (or tradeoff) for the benefits of mechanical advantage? The greater the mechanical advantage, the more rope is required to add pulleys, increasing the amount (distance) you have to pull to move the object.

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Appendix A Simple Machines

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Appendix B Simple Machines

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Appendix C Simple Machines

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Appendix C Simple Machines

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Appendix C Simple Machines

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Appendix D Simple Machines

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