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**Work, Power, and Simple Machines**

Chapter 14 Work, Power, and Simple Machines

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**Force acting through a distance**

Work Must be movement Work = force x distance Joule meters Newton

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**If the direction of the movement is Not the same as the force… NO work is done!**

applied force Motion Motion Applied force

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Is Work Done?

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SI unit of Work Joule = Newton x meter (J) = N x m

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**A weight lifter lifts a 1600 newton barbell over his head**

A weight lifter lifts a 1600 newton barbell over his head. The barbell is lifted to a height of 2.0 meters. Calculate the work done. Work = Force x Distance

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**A student rows a boat across a still pond with a force of 72 newtons**

A student rows a boat across a still pond with a force of 72 newtons. The student travels a distance of 13 meters Calculate the work done. Work = Force x Distance

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Involves time Power How fast is work done? Power = Work / time Watts Joules seconds Large amounts of power are measured in kilowatts

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**Doing work faster requires more power.**

You can increase the amount of work done in a given time. OR You can do a given amount of work in less time.

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SI unit of Power Watt = Joule second (W) = J/s

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A truck pulls a trailer at a constant velocity for 100 m while exerting a force of 480 N for 1 minute (60 s). Calculate the work done and the power. Work = Force x Distance Power = Work time

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**Complete the Math Practice on page 415**

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Horse-power equal to 750 watts 1 strong horse can move a 750 N object 1 meter in 1 second 1 hp = small electric motor family car = 100 hp diesel train = 10,000 hp

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**Energy, Work, Power, and Energy Worksheet Answers**

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Part 1: Work and Power 1. Amy uses 20-N of force to push a lawn mower 10meters. How much work does she do?

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Part 1: Work and Power 2. Frank does 2400-J of work in climbing a set of stairs. If he does the work in 6 seconds, what is his power output?

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Part 1: Work and Power 3. A girl weighing 420 Newtons takes 55 seconds to climb a flight of stairs 18 meters high. What is her power output vertically?

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Part 1: Work and Power 4. How much work does an elephant do while moving a circus wagon 20 meters with a pulling force of 200-N?

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Part 1: Work and Power 5. A 40 N force is used to push a 2.00 kg cart a distance of 5 meters. What is the work done on the cart?

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Part 1: Work and Power 6. A 900-N mountain climber scales a 100 meter cliff. How much work is done by the mountain climber?

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Part 1: Work and Power 7. A small motor does applies a 200N force over 10m in 20 seconds. What is the power of the motor in watts?

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Section 14:2 WORK AND MACHINES Yes…machines do work

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**makes work easier increase force increase distance**

Machine increase force increase distance change the direction Work Input Work applied to the machine by you Work Output Work done by the machine

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Work Input = Input Force x Input Distance Work Output = Output Force x Output Distance

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**14:3 Mechanical Advantage**

Number of times a machine multiplies the force applied Ex. Cracking Pecans

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**Actual Mechanical Advantage**

The mechanical advantage determined by measuring the actual forces acting on a machine. Actual Mechanical Advantage = Output Force Input Force

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**Ideal Mechanical Advantage**

The mechanical advantage in the absence of friction. Ideal Mechanical Advantage = Input Distance Output Distance

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**A woman drives her car onto wheel ramps to perform some repairs**

A woman drives her car onto wheel ramps to perform some repairs. If she drives a distance of 1.8 meters along the ramp to raise the car 0.3 meter, what is the ideal mechanical advantage (IMA) of the wheel ramps? IMA = Input Distance Output Distance

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**Complete the Math Practice on Page 425.**

6 10 m

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**Part 2: Machines and Mechanical Advantage**

1.

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2.

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3.

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Part 3: Torque The drawing above represents a wrench. The left end of the wrench is attached to a bolt. Four equal forces of 100N are applied as indicated in the drawing. A. A 100N force would cause the most torque if it was placed at which letter above? (Why) B. What is the torque at A C. What is the torque at C

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**4. What is the boy weight in order for the see-saw to be in equilibrium?**

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**5. How far is the boy from the fulcrum in the see-saw in equilibrium below?**

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**How much work input is used to create work output**

Efficiency Eff. = Work output x 100% Work input Ex. Gas mileage = Miles driven Gallons of gas

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**Complete the Math Practice on Page 426.**

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**14:4Simple Machines Does work with one movement Six Types:**

√ Lever √ Wheel & Axle √ Inclined Plane √ Wedge √ Screw √ Pulley

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Lever bar that is free to pivot around a fixed point called a ________. fulcrum Classified in 3 categories

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fulcrum 1st class: The _______ is located between the ______ and the _________. effort resistance Output Force Input Force Fulcrum Ex. Seesaw, crowbar

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**2nd class: The ________ is located between the ______ and the _______. **

resistance fulcrum effort Output Force Input Force Fulcrum Ex. Wheelbarrow, hole punch

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effort 3rd class: The ________ is located between the ______ and the __________. fulcrum resistance Output Force fulcrum Input Force Ex. Baseball bat, rake

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**Wheel and Axle _______ sized wheels rotating together.**

Different Ex: door knob, tires, can opener

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**Inclined Plane Sloping surfa ce Ex: ramp, slide IMA = length/height 12**

Sloping surfa ce Ex: ramp, slide IMA = length/height 12 5 4 4

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Wedge An inclined plane that moves Ex. Axe, sledgehammer

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**Screw An inclined plane wrapped around a cylinder**

An inclined plane wrapped around a cylinder Ex. Light bulb, bolts, lids

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**Let’s make our own screw**

Take out a sheet of paper. Fold it at an angle. Tear along the crease. Slowly wrap it around your pen or pencil. Turn your pen/pencil.

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**PULLEYS _______ with a rope, chain, or cable. Three different types**

Cylinder _______ with a rope, chain, or cable. Three different types

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**A wheel is attached in a fixed location.**

Fixed Pulley A wheel is attached in a fixed location. Rotate in place. Ex. flagpole

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**Attached to the moving object.**

Movable Pulley Attached to the moving object. Ex. Sails

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Pulley System Combines fixed and movable pulleys Ex. Crane

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**Bill Nye simple machines**

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Compound Machines Combination of two or more simple machines that operate together. Ex. Car, watch, washing machine

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