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WORK, POWER & Simple Machines. WORK, POWER & Simple Machines. What is the hardest, most difficult job, task, or chore you have ever done? Who is the most powerful person in the world?. 3) Dictionary Mental or physical exertion.
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WORK,POWER & Simple Machines What is the hardest, most difficult job, task, or chore you have ever done? Who is the most powerful person in the world?
3) Dictionary Mental or physical exertion. Scientific the product of force applied to an object and the distance the object moves.
4) 3 examples of work Lifting, pushing, pulling
5) 3 requirements for work are: • A force must be applied. • Object must move. • Motion must be in the direction of the force.
Work or Not? • According to the scientific definition, what is work and what is not? • a teacher lecturing to her class • a mouse pushing a piece of cheese with its nose across the floor
Work or Not? • According to the scientific definition, what is work and what is not? • a teacher lecturing to her class • a mouse pushing a piece of cheese with its nose across the floor
What’s work? • A scientist delivers a speech to an audience of his peers. • A body builder lifts 350 pounds above his head. • A mother carries her baby from room to room. • A father pushes a baby in a carriage. • A woman carries a 20 kg grocery bag to her car?
What’s work? • A scientist delivers a speech to an audience of his peers. No • A body builder lifts 350 pounds above his head. Yes • A mother carries her baby from room to room. No • A father pushes a baby in a carriage. Yes • A woman carries a 20 km grocery bag to her car? No
Formula for work Work = Force x Distance • The unit of force is newtons • The unit of distance is meters • The unit of work is newton-meters • One newton-meter is equal to one joule • So, the unit of work is a joule
W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?
W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done? 200 joules (W = 20N x 10m)
8) How is work calculated? Work = force x distance W = Fd (draw a triangle) The unit is a newton x meter = 1 Nm A Nm is called a joule (J)
9) James Prescott Joule Foot-pound (ft-lb) Torque wrench
You your friend Mr. Blue WE ALL DO THE SAME AMOUNT OF WORK! Every body moves one metric ton of dirt 25 meters
12) NO! work = F x d time does not factor into scientific work. 13) POWER
15) If you said MR. Blue you are right. 16) Power = work / time P = W / t joule divided by a second WATT (W) (J/s or Nm/s)
Power • Power is the rate at which work is done. • Power = Work*/Time *(force x distance) • The unit of power is the watt.
18) James Watt (1736-1819) 19) Improved the steam engine & started the industrial revolution
Check for Understanding 1.Two physics students, Ben and Bonnie, are in the weightlifting room. Bonnie lifts the 50 kg barbell over her head (approximately .60 m) 10 times in one minute; Ben lifts the 50 kg barbell the same distance over his head 10 times in 10 seconds. Which student does the most work? Which student delivers the most power? Explain your answers.
Ben and Bonnie do the same amount of work; they apply the same force to lift the same barbell the same distance above their heads. Yet, Ben is the most powerful since he does the same work in less time. Power and time are inversely proportional.
2. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s/s a distance of 10 meters in 5 seconds? This problem requires you to use the formulas for force, work, and power all in the correct order. Force=Mass x Acceleration Work=Force x Distance Power = Work/Time
2. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s/s a distance of 10 meters in 5 seconds? This problem requires you to use the formulas for force, work, and power all in the correct order. Force=Mass x Acceleration Force=10 x 2 Force=20 N Work=Force x Distance Work = 20 x 10 Work = 200 Joules Power = Work/Time Power = 200/5 Power = 40 watts
19) Horsepower (hp) 20) 1 hp = 746 W
21) Lawnmower engine 3-100,000 hp
A schematic diagram of relaxation oscillator, camera motor, hairdryer, power tools, & electric train ( nW-MW)
23) What is a machine? Any device that makes work easier.
24) Machines multiply forces,multiply distance ( increase speed), or change the direction of the force 25)
26) Work input (Wi) is the work you do on the machine. Wi = Feffort x deffort 27) Work output (Wo) is the work the machine does on the object or load. Wo = Fresistance x dresistance
28) Efficiency (EFF) & Mechanical Advantage (MA) Efficiency is the ratio of use-ful work output to neces-sary work input. EFF = Wo/Wi x 100 = %
Transformer (98%), car (35%), & human brain (?)
30) complete the problem 31) It depends, friction/sound 32) Mechanical Advantage (AMA) is the number of times forces are multiplied. Ideal (theoretical) Mechanical Advantage (IMA) - is the number of times distances are multiplied
AMA = F resistance / F effortAMA = 10 000 N / 10 N =? IMA = d effort / d resistance IMA = 100 m / 10 m =?
AMA or IMA is unitless Note you may use a “x” like 100x, 2x, .5x etc An ideal machine is friction-less, weightless, massless, and impossible to build.
34) Stick, rock, club, pre-stone age, Africa 35) A simple machine does work with one movement. 36) 1) lever 2) inclined plane 3) wheel & axle 4) wedge 5) pulley 6) screw
Levers are rigid objects that move at a fulcrum (pivot point) to create MA.
Classes of Levers - First, Second and Third resistance Fulcrum is always between the effort & resistance
It is as easy as 1 2 3 F R E
Pulleys are ropes, belts, chains, etc. wrapped around a wheel & axle
Inclined Plane (IP) a slanted surface used to lift an object.
