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Work and Machines What Is Work? How Machines Do Work Simple Machines Table of Contents

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Work and Machines Calculating Power A tow truck exerts a force of 11,000 N to pull a car out of a ditch. It moves the car a distance of 5 m in 25 seconds. What is the power of the tow truck? What quantity are you trying to calculate? The Power (P) the tow truck uses to pull the car = __ What formula contains the given quantities and the unknown quantity? Power = Work/Time = (Force X Distance)/Time Perform the calculation. Power = (11,000 N X 5.0 m)/25 s Power = (55,000 Nm)/25 s or 55,000 J/25 s Power = 2,200 J/s = 2,200 W 1 Joule per second = 1 Watt 1000 Watts = 1 kilowatt or 1000 W = 1 kW - What Is Work?

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Work and Machines Calculating Power A tow truck exerts a force of 11,000 N to pull a car out of a ditch. It moves the car a distance of 5 m in 25 seconds. What is the power of the tow truck? Look Back and Check Does your answer make sense? The answer tells you that the tow truck used 2,200 W to pull the car. This value is about the same power that three horses would exert, so the answer is reasonable. - What Is Work?

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Work and Machines Calculating Power Practice Problem A motor exerts a force of 12,000 N to lift an elevator 8.0 m in 6.0 seconds. What is the power produced by the motor? (12,000 N x 8.0 m)/6.0 s = 16,000 W or 16 kW - What Is Work?

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Work and Machines Calculating kilowatt-hours & Cost Suppose you use your DVD player & TV with a combined power rating of 250 W for 40 hours over the course of a month. How many kilowatt-hours did you add to the electric bill? Remember to convert units. How much money did you add to the electric bill if the electric company charges 7 cents ($0.07) per kWh? 250 W = 0.250 kW Amount of kWh = 0.250 kW x 40 hours = 10 kWh Cost = 10 kWh x $0.07 per kWh = $0.70 or 70 cents - What Is Work?

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Work and Machines Experiment Problem from the Forces Test Suzie and Markie are attempting to discover how to make moving large objects easier. They both believe that lighter objects are easier to move across a surface. They design an experiment to test out their prediction using a small wooden cart, a force sensor, and weights. Hypothesis- Lighter objects are easier to move across a surface. Ind. Variable- weight or mass Dep. Variable- frictional force or force required to move the object or distance moved in a certain amount of time Constants- same surface, same incline, same distance moved, same force sensor, same amount of pull/time for each measurement

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Work and Machines Experiment Problems Determine the hypothesis, independent variable, dependent variable, and 2 or more constants for the experiment: A student believes that bacteria grows quicker in warmer environments and slower in a cooler environment. This student is using petri dishes (little plastic dishes) and incubators of varying temperatures to cultivate the bacteria. Hypothesis- Bacteria will grow quicker the warmer it gets (as temperature goes up). Ind. Variable- Temperature Dep. Variable- Amount of bacteria grown Constants- Same size petri dishes, same amount of bacteria in each dish to start with, same amount of light, etc.

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Work and Machines Plant Experiment Determine the independent variable(s), dependent variable, 2 or more constants, and the control group: Flowers in a greenhouse are fertilized with a mixture of nitrogen (N), phosphorus (P), and potassium (K). A student has used different amounts of these parts of fertilizer to determine which component is most responsible for good growth. Examine the table. Ind. Variables- Amount of different fertilizers (N, P, & K) Dep. Variable- Amount of Plant growth Constants- Amount of soil, amount of water added to the plant, amount of sunlight Control Group- Plant C (b/c it doesn’t have any fertilizer, so the student is seeing how much the plant would grow normally- without fertilizer) Plant APlant BPlant CPlant D N = 90N = 5N = 0N = 5 P = 5P = 90P = 0P = 5 K = 5 K = 0K = 90

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Work and Machines Noggin Knockers

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Work and Machines Electricity Usage and Power The amount of money you add to the electric bill can be determined by how long you use certain appliances and the power rating of those appliances. Power is the rate at which the work gets done, so power is the amount of work done in a certain amount of time. Power = Work/Time or (Force x Distance)/Time And Power = strength of the electric current x voltage Power is measured in Watts (W) or kilowatts (kW). Examples- Light Bulbs range from 40 W to 100 W. 1 Watt = 1 (N x m)/s or 1 J/s 1000 Watts = 1 kilowatt

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Work and Machines Electricity Usage and Power Electric companies charge about 7 cents ($0.07) per kilowatt-hour (kWh). So, if use an appliance with a 1000 W (or 1 kW) power rating for 100 hours over the course of a month, then you used 1 kW x 100 hours = 100 kWh. To determine the money added to the bill, multiply the kWh by the money per kWh… 100 kWh x 0.07 dollars/kWh = $7.00

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Work and Machines Which of the following is NOT an example of doing work? A.Pushing a cart around in the grocery store. B.Lifting your books. C.Holding a person straight above your head. D.Pulling a person out of quicksand. E.Me in 10 years.

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Work and Machines If a 100 N force to the right is used to move a couch 5 m to the right, then how much work was done? A.500 N x m or 500 Joules B.20 N x m or 20 Joules C.500 N D.No work was done.

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Work and Machines The rate at which work gets done is A.Very slow if I’m in charge. B.Force. C.Work. D.Power.

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Work and Machines To calculate power, you divide work (or force x distance) by A.Work. B.Time. C.Force. D.Distance.

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Work and Machines Which of the following are units for power? A.Newton x meters (N x m) B.Newtons C.Joules (J) or Joules x seconds (J x s) D.Watts (W) or kilowatts (kW)

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Work and Machines 2000 W = ___________ kW A.2 kW B.20 kW C.200 kW D.2 cans of A & W

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Work and Machines How much power is required of you if you use 50 N to lift your books 1 m in 2 seconds? A.100 W B.50 W C.25 W D.0 W

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Work and Machines Your electric bill is determined by multiplying a cost of about 7 cents ($0.07) for every A.Watt-seconds. B.Kilowatt-hour. C.Kilowatt-seconds. D.Watt-minutes.

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Work and Machines Suppose you play Call of Duty: Modern Warfare 3 for 700 hours over the course of a month. The combined power rating of the TV and the X-Box is 500 Watts. What is the number of kWh for your gaming? Remember to convert units if needed. A.350,000 kWh B.1200 kWh C.350 kWh D.0.350 kWh

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Work and Machines So if you had to pay 7 cents ($0.07) per kWh and your gaming racked up 350 kWh, then how much money did you add to the electric bill due to your gaming addiction? A.$24.50 B.$2.45 C.$2450 D.$50.00

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Work and Machines Homework- p. 113: 1a, 1b, 1c, 2b, 2c, 3b, & 4 1a- Work is when you apply a force on an object and this causes the object to move a certain distance. 1b- The object has to move in the same direction in which the force is applied. 1c- Work is done for rolling a bowling ball and kicking a football. 2b- Work = Force x Distance (in same direction as the force) 2c- Same amount of work b/c 2 N x 3 m = 6 J and so does 3 N x 2 m 3b- Power is Work divided by the time it takes to get the work done. 4- P = (Force x Distance)/Time = (22 N x 3.0 m)/6.0 s = 11 Watts

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Work and Machines Noggin Knockers

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Work and Machines Learning Objectives 1.Identify when work is done on an object. Force, Movement in the same direction as the force 2.Calculate the work done on an object. 3.Define and calculate power.

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Work and Machines - What Is Work? The Meaning of Work Work is done on an object when the object moves in the same direction in which the force is exerted. Work = Force x distance

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Work and Machines Calculating Work A tow truck exerts a force of 11,000 N to pull a car out of a ditch. It moves the car a distance of 5 m. What is the work done by the tow truck? Work = Force x distance (in the direction of the force) Work = 11,000 N x 5.0 m = 55,000 N x m (Newton meters) 1 N x m = 1 Joule = 1 J So, Work of the tow truck = 55,000 Joules or 55,000 J - What Is Work?

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Work and Machines Calculating Work Suppose you get super strong exert a force of 500 N by moving a person 2 m out of the way of a moving truck. How much work did you do? Work = 500 N x 2 m = 1000 N x m (Newton-meters) So, Work = 1000 Joules or 1000 J - What Is Work?

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Work and Machines Learning Objectives 1.Explain how machines make work easier. Lowering the applied force and/or Changing direction 2.Determine the mechanical advantage of a machine (relative to 1). 3.Calculate the efficiency of a machine.

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Work and Machines - How Machines Do Work Input and Output Forces Examine the input and output forces for a shovel. The input force is also called the applied force.

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Work and Machines Rise of the Machines Activity In your lab notebook (this is not a FULL lab write-up): ramp gear system of a bike 1.Determine which of the following are machines: ramp, pliers, screwdriver, baseball, ruler, coat zipper, paper, tweezers, gear system of a bike. 2.For the ones that are machines, draw a diagram of the machine and draw the input (or applied) force and output force arrows.

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Work and Machines Diagrams- Ramp & Pliers

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Work and Machines Diagrams- Screwdriver & Coat Zipper

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Work and Machines Diagrams- Tweezers & Bike

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Work and Machines - How Machines Do Work What Is a Machine? A machine makes work easier by LOWERING the amount of force you exert (by increasing the distance over which you exert your force), or the direction in which you exert your force. Examples: 1.Lowering the applied force- Turning the knob to turn the hose on 2.Changing Direction- Lifting weights using a pulley

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Work and Machines Rise of the Machines (Part 2) Determine if the machine lowers the applied force OR changes direction: ramp, pliers, screwdriver, coat zipper, seesaw, & putting up a flag on a flag pole. H int: If it’s difficult to use your hands for a task (making it so you need to use the machine for a task), then that machine probably lowers the applied force. Ramp- lowers the applied force (output force is greater than the input force of pushing an object up a ramp) Pliers- lowers the applied force (output force>input force) Screwdriver- lowers the applied force (output force>input force) Coat Zipper- lowers the applied force (input force is low compared to the output force pushing outward) Seesaw & Flag pole- Changing directions (pull/push downward & the flag or other side of the seesaw goes up)

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Work and Machines Which of the following is a simple machine? A.Diagram 1 B.Diagram 2 C.Diagram 3 D.Diagram 4 E.Diagram 5

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Work and Machines The force you apply when you first use a machine is called the A.Output force. B.Input or Applied force. C.Inner force. D.Jedi Knight force.

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Work and Machines Machines make work easier by A.Lowering the initial effort required to do the work. B.Lowering the applied force. C.Changing directions. D.All of the above.

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Work and Machines Which of the following machines USUALLY causes a change in direction? A.pulleys B.Saying mean things to someone stronger than you C.ramps D.tweezers

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Work and Machines Which of the following lowers the applied force? A.A bike in high gear compared to lower gears B.tweezers C.screwdriver D.A pulley

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Work and Machines Which of the following is true about why a steering wheel connected to an axle is used in vehicles? A.More force on the steering wheel is needed over a shorter distance to make the vehicle turn. B.Less force on the steering wheel is needed over a larger distance to make the vehicle turn. C.More force on the steering wheel is needed over a larger distance to cause the vehicle to turn. D.Less force on the steering wheel is needed over a shorter distance to cause the vehicle to turn. Arrows show distance traveled, not force!

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Work and Machines Suppose you are using a screwdriver, and the output force is 100 N. Which of the following is a possible applied force? Hint: Keep in mind how this machine makes work easier and double check to ensure your answer makes sense. A.200 N B.150 N C.40 N D.0 N

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Work and Machines Learning Objectives 1.Calculate the mechanical advantage of a machine. /Output Force/Input Force, Relative to 1 (Less than 1, Equal to 1, Greater than 1)

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Work and Machines - How Machines Do Work Input and Output Work The amount of input work done by the gardener equals the amount of output work done by the shovel. Mechanical Advantage of a machine = output force/applied force M.A. = F o /F a

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Work and Machines Mechanical Advantages of Ramps Goal: Determine the mechanical advantage for inclined planes (ramps) with varying steepness by using M.A. = F o /F a equation for M.A Hypothesis: For the inclined planes, determine if you believe the mechanical advantage will be greater than 1, equal to 1, or less than 1. Explain why you predict this based upon how the machines work and the equation for M.A. Background: 2.5 N. Output force = the ____________ of the cart = 2.5 N. Procedure (Organize your results in a Table- on the next slide): 3 different steepnesses 1.Determine the applied force (by pushing the go-car up the ramp with the force sensor) and output force for 3 different steepnesses of the ramp. 2.Calculate the mechanical advantage for the 3 ramp setups.

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Work and Machines Conclusions (answer in complete sentences): 1.Which ramp had the greatest mechanical advantage? Explain why. 2.Did any setup have a mechanical advantage less than 1? Explain why or why not. Hint- Use the M.A. equation & the terms applied force & output force. lowers the applied force 3.Based upon your data, determine which M.A. corresponds to the machine that lowers the applied force: 0.6, 2.0, & 1.0. Machine/SetupOutput Force F o (Weight in N) Applied Force F a (N) Mechanical Advantage (F o /F a ) Ramp- slightly steep Ramp- mid-steepness Ramp- high steepness Data Table & Conclusions

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Work and Machines Mechanical Advantage of a Fixed Pulley After the Conclusions from the previous experiment (Mechanical Advantages of Ramps), record your data and conclusions for the M.A. of a fixed pulley. Background: The output force (once again) = the _________ in N. Setup: Tie a long piece of string to the force sensor hook. Make sure the weights are not hanging and the string is loose with some slack. Next, tie the untied end of the string to the rubber band around the weights. Determine the output force. Then untie the string and thread it through the pulley track. Tie it to the weights. Results: 1.Measure the applied force by pulling the force sensor down (which should pull the weight up). (F o /F a ). 2.Calculate the mechanical advantage (F o /F a ). Conclusions: 1.Was the mechanical advantage close to 1? If so, then explain why in terms of the input force compared to the output force. lowering the applied forcechanging direction 2.So if the M.A. = about 1, then the machine probably makes work easier by which of the following: lowering the applied force OR changing direction.

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Work and Machines Mechanical Advantages of Machines Procedure (In groups) Record the following in your lab notebook with the title above. Record the following in your lab notebook with the title above. Determine if the machine lowers the applied force OR changes the direction of the force; then determine which is greater- the output or the applied force; lastly, determine it’s M.A. relative to 1 (, or =) for… –Inclined Plane (a ramp)- Refer to the ramp experiment. –A fixed pulley (like a flagpole)- Refer to the Fixed Pulley experiment. –A wedge (like a coat zipper or an ax) –Wheel and axle (like a screwdriver) –A screw (a winding inclined plane)- Refer to the ramp experiment.

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Work and Machines Graphic Organizer (Table) for Machines Type of Machine Lowers the Applied Force OR Changes the Direction of the Force Output Force (>, <, or =) Applied force Mechanical Advantage relative to 1 (> 1, < 1, = 1) Inclined Plane (Ramp) Lowers the applied force >> 1 Fixed Pulley Changes DirectionAbout == 1 Wedge (ax, zipper) Lowers the applied force >> 1 Wheel & Axle (screwdriver, doorknob) Lowers the applied force >> 1 A screw Lowers the applied force >> 1

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Work and Machines Input Work vs. Output Work Ramp example containing data from the experiment: Applied Force = 1.0 NOutput force = 3.0 N Input Distance = 1 mOutput distance = 0.33 m Input Work = 1.0 N x 1 m = 1 N x m or 1 J Output Work = 3.0 N x 0.33 m = 1.0 J Input Work = Output Work without friction

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Work and Machines Calculating Efficiency You do 250,000 J of work to cut a lawn with a hand mower. If the work done by the mower is 200,000 J, what is the efficiency of the lawn mower? What is the main force that will resist the motion of the parts of a machine and cause the efficiency to be less than 100%? FRICTION What information have you been given? Input Work (W input ) = 250,000 J Output Work (W output ) = 200,000 J - How Machines Do Work

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Work and Machines Calculating Efficiency You do 250,000 J of work to cut a lawn with a hand mower. If the work done by the mower is 200,000 J, what is the efficiency of the lawn mower? Plan and Solve What quantity are you trying to calculate? The efficiency of the lawn mower = __ What formula contains the given quantities and the unknown quantity? Efficiency = Output work/Input work X 100% Perform the calculation. Efficiency = 200,000 J/250,000 J X 100% Efficiency = 0.8 X 100% = 80% The efficiency of the lawn mower is 80 percent. - How Machines Do Work

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Work and Machines Calculating Efficiency You do 250,000 J of work to cut a lawn with a hand mower. If the work done by the mower is 200,000 J, what is the efficiency of the lawn mower? Look Back and Check Does your answer make sense? An efficiency of 80 percent means that 80 out of every 100 J of work went into cutting the lawn. This answer makes sense because most of the input work is converted to output work. - How Machines Do Work

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Work and Machines Real vs. Ideal Machines Ideal machines would operate at 100% efficiency, while real machines operate at less than 100% efficiency due to friction. Real Machine < 100% EfficiencyIdeal Machine = 100% Efficiency

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Work and Machines the machine exerts on an object The force the machine exerts on an object is called the ___________ force. A.Output B.Input C.Applied D.Same

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Work and Machines The output force divided by the applied force is the A.Efficiency of the machine. B.Mechanical advantage of the machine. C.Ratio of good to bad parts of the machine. D.Only calculation that has to be greater than 1.

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Work and Machines Which of the following will have a mechanical advantage = 1? A.Shovel B.Screwdriver C.A fixed pulley D.Broom or 3 rd class lever

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Work and Machines If the output force is greater than the input or applied force, then the M.A. is A.Less than 1 like a broom B.Greater than 1 like a screwdriver C.Equal to 1 like a fixed pulley D.None of the above are completely true.

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Work and Machines The efficiency of a ramp is 76%. Why is it not 100% since input work is supposed to equal output work? A.The reaction force of the machine on the person causes this difference. B.It is 100%, the first statement is a lie! C.Friction causes the output work to be less than the input work. D.Gravity causes the output work to be less than the input work.

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Work and Machines Contrast real and ideal machines. A.Real machines < 100% efficiency, while ideal machines = 100% efficiency. B.Real Machines = 100% efficiency, while ideal machines < 100& efficiency. C.Real Machines > 100% efficiency, while ideal machines = 100% efficiency. D.Real Machines keep it real, while the only ideal machine is my 8 th grade science teacher.

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Work and Machines End of Section: How Machines Do Work

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Work and Machines Noggin Knockers/Hwk.- p. 113- 1c, p. 121: 1b, 1c, 2b, 2c, 3c 12 pts. total- 2 points each) 1- Rolling a bowling ball & kicking a football. 2- Screwdrivers lower the applied force (the amount of force or effort you exert). 3- M.A. = 1 4- M.A. = 80 N/40 N = 2 5- Real Machines have less than 100 % efficiency due to friction. 6- ( (( (b) 70 N (applied force/force you exert on the ax should be less than the output force/force the ax exerts on the piece of wood)

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Work and Machines Learning Objectives 1.Describe the 6 types of simple machines including the different pulley setups and different classes of levers. (See Mechanical Advantages of Machines in your lab notebook) 2.Describe the mechanical advantage (relative to 1) for each simple machine in terms of output vs. applied force. (See Mechanical Advantages of Machines in your lab notebook)

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Work and Machines Pulley Demo (2 Pulley- Fixed and Movable/Block & Tackle) Output Force = the object’s ___________. Note that every time a machine lifts/moves an object to a different location, the object’s weight is the output force. Applied Force = Person’s ________ on the rope downward. Results: Output force is (greater than, less than, or equal to) the input force. Conclusion: So, the Mechanical Advantage of this pulley system and others with 2 or more pulleys is (greater than, less than, or equal to) 1.

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Work and Machines - Simple Machines Pulley A pulley is a simple machine made of a grooved wheel with a rope or cable wrapped around it.

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Work and Machines - Simple Machines Inclined Plane An inclined plane is a flat, sloped surface.

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Work and Machines - Simple Machines Screws A screw can be thought of as an inclined plane wrapped around a cylinder.

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Work and Machines - Simple Machines Wedge A wedge is a device that is thick at one end and tapers to a thin edge at the other end.

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Work and Machines - Simple Machines Wheel and Axle A wheel and axle is a simple machine made of two circular or cylindrical objects fastened together that rotate about a common axis.

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Work and Machines - Simple Machines Levers A lever is a ridged bar that is free to pivot, or rotate, on a fixed point. 1 st class lever

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Work and Machines Lever Experiment Goal- Draw and model the 3 classes of levers shown below & determine how they make work easier by comparing the input or applied force to the output force (weights = 2.8 N). Results- Record the applied force for each lever and calculate the M.A for each class of lever. lower the applied force changing the direction both If so, which one(s)? Conclusion- State which levers lower the applied force and which levers make work easier by changing the direction of the force. Are there any levers that do both (lower the applied force and change the direction of the force)? If so, which one(s)? 1 st class 2 nd class 3 rd class

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Work and Machines Lever Experiment Extension (No lab write-up) Goal- Determine how lifting a bunch of books (with a heavy load weight) compares to using a 1 st class lever to lift the books. Procedure 1.Lift the books and remember how much force it felt like you were exerting. 2.Then repeat using a 1 st class lever. Results/Conclusions make it easier applied force Did the lever make it easier to lift the books? If so, then how? Hint- Compare your applied force using the lever to the amount of force that it took to just lift the books (output force/weight).

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Work and Machines - Simple Machines Levers Levers are classified according to the location of the fulcrum relative to the input and output forces.

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Work and Machines Identification of Real World Examples Identify the following examples of simple machines as 1 of the 6 previously discussed (be specific with any levers): 1.Shoving a shovel straight into the ground 2.Steering system of a bike or car 3.Ramp or a screw 4.Wheelbarrow 5.Pliers 6.A construction crane

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Work and Machines - Simple Machines Simple Machines in the Body Most of the machines in your body are levers that consist of bones and muscles.

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Work and Machines More Simple Machines in the Body Teeth- Wedges Turn your forearm at the elbow- Wheel & Axle Muscle used to raise your eyes- Pulley

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Work and Machines - Simple Machines Compound Machines compound machine A compound machine is a machine that utilizes two or more simple machines.

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Work and Machines If the input force for the lever below is 100 N, then the output force or load weight would have to be A.Less than 100 N. B.Greater than 100 N. C.Equal to 100 N. D.Equal to 0 N.

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Work and Machines For a 1 st class lever to lower the applied force, where must the fulcrum or pivot point be? A.Closer to the input force. B.Closer to the output force. C.Directly in the middle. D.At the other end.

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Work and Machines If the weight of the load is 100 N, then which of the following is a possible value for the input or applied force? A.50 N B.100 N C.150 N D.200 N

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Work and Machines Your body includes several simple machines such as A.Teeth acting as wedges. B.Eye raising via a pulley. C.Rotating your forearm is an example of a wheel and axle. D.Lifting an object up using your arm and bending your elbow is an example of a lever. E.All of the above are examples of simple machines in your body.

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Work and Machines A machine composed of 2 or more simple machines is a A.Simpler machine. B.Complex machine. C.Compound machine. D.Machine that operates at 100% efficiency.

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Work and Machines Which of the following is an example of a compound machine? A.Using a meter stick as a 1 st class lever B.Fixed pulley C.Ramp D.Scissors

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Work and Machines Work & Machines Quiz Answers 1.C- pushing a box up a ramp (object moves in the direction of the force) 2.E- lowering applied force and changing the direction of the force 3.D- 100% machine efficiency (output work = input work) 4.A- output force greater than input force (M.A. = F o /F a ; ex.- 3/1 = 3 which is greater than 1) 5.D- 3.0 (see example above- applied force is the lesser force) 6.A- Equal to 1 (output force = input force; ex.- 2/2 = 1) 7.C- less than 10 N (Refer to Lever Expt.) 8.C- Smaller input force over a larger distance etc. (Examine diagram) 9.B- 30 N (only force greater than 20 N, since F o > F a )

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Work and Machines Work & Machines Quiz Answers 10.B- pulley that changes the direction fo the force (pull down and flag goes up) 11.A- Diagram 1 has the most pulleys 12.A- inclined plane (refer to notes) 13.B- screw (refer to notes) 14.B- Lever (hammer head is the pivot point/fulcrum) 15.D- Lever decreases the amount of force (AKA the applied force) required to lift the load (Refer to Lever Expt.) 16.A- inclined plane (ramp) and wheel and axle (from wheelchair) 17.C- Teeth (cut through food) 18.B- the human body (consists of levers- neck, foot, arm; pulley- eye raising, wedges- teeth, etc.)

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Work and Machines Work & Machines Practice Quiz Answers 1.When a force is applied to an object and it moves in the same direction as the force. 2.Friction 3.Applied force is lower for machines with M.A.’s greater than 1. 4.Greater than 5 N (because the applied is lower than the output force) 5.M.A. = 1, then that machine ONLY changes the direction of the force. 6.1 st class lever: lowers the applied force and changes the direction of the force. 2 nd class lever: lowers the applied force. 7.Applied force is less than 100 N (because the applied force is lower than the output force/load weight). 8.A LOWER applied force is exerted over a GREATER distance (on the wheel) while a larger output force is over a shorter distance (on the axle).

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Work and Machines Work & Machines Practice Quiz Answers 9.Multiple pulleys result in a lower applied force (so it would be easier to lift an object with a heavier weight) 10.(a) Ramp (b) Screw (c) Door stopper, knife, ax, teeth (d) Doorknob, steering wheel, rotating your forearm (e) Seesaw, pliers, scissors, lifting your head (f) Wheelbarrow, door, lifting your heel (g) Raising a flag on a flagpole, construction cranes, eye raising 11.A compound machine is 2 or more simple machines put together. (examples include scissors, the human body, wheelbarrow)

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Work and Machines Previewing Visuals Before you read, preview Figure 17. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions. Three Classes of Levers Q. What are the three classes of levers? A. The three classes of levers are first-class levers, second-class levers, and third-class levers. Q. How do the three classes of levers differ? A. They differ in the position of the fulcrum, input force, and output force. - Simple Machines

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Work and Machines Levers Click the Video button to watch a movie about levers. - Simple Machines

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Work and Machines Pulleys Click the Video button to watch a movie about pulleys. - Simple Machines

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Work and Machines End of Section: Simple Machines

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Work and Machines Graphic Organizer Wheel and axle Simple Machine Mechanical Advantage Example Inclined plane Length of incline ÷ Height of incline Ramp Radius of wheel ÷ Radius of axle Screwdriver Wedge Length of wedge ÷ Width of wedge Ax Screw Length around threads ÷ Length of screw Screw Lever Distance from fulcrum to input force ÷ Distance from fulcrum to output force Seesaw Pulley Number of sections of supporting rope Flagpole

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Work and Machines End of Section: Graphic Organizer

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Chapter 12 Work and Machines

Chapter 12 Work and Machines

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