# Work, Power, and Simple Machines

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Work, Power, and Simple Machines
Chapter 14 Work, Power, and Simple Machines

Force acting through a distance
Work Must be movement Work = force x distance Joule meters Newton

If the direction of the movement is Not the same as the force… NO work is done!
applied force Motion  Motion  Applied force 

Is Work Done?

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

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

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

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

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.

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

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

Complete the Math Practice on page 415

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

Energy, Work, Power, and Energy Worksheet Answers

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

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?

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?

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?

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?

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?

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?

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

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

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

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

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

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

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

Complete the Math Practice on Page 425.
6 10 m

Part 2: Machines and Mechanical Advantage
1.

2.

3.

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

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

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

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

Complete the Math Practice on Page 426.

14:4Simple Machines Does work with one movement Six Types:
√ Lever √ Wheel & Axle √ Inclined Plane √ Wedge √ Screw √ Pulley

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

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

2nd class: The ________ is located between the ______ and the _______.
resistance fulcrum effort Output Force Input Force Fulcrum Ex. Wheelbarrow, hole punch

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

Wheel and Axle _______ sized wheels rotating together.
Different Ex: door knob, tires, can opener

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

Wedge An inclined plane that moves Ex. Axe, sledgehammer

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

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.

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

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

Attached to the moving object.
Movable Pulley Attached to the moving object. Ex. Sails

Pulley System Combines fixed and movable pulleys Ex. Crane

Bill Nye simple machines

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