WORK,WORK, POWER POWER & & Simple Simple MachinesMachines

WORK,WORK, POWER POWER & & Simple MachinesSimple Machines

1)1) What is the hardest, What is the hardest, most difficult job, task, most difficult job, task, or chore you have ever or chore you have ever done?done?

2)2) Who is the most Who is the most powerful person in the powerful person in the world?world?

3) Dictionary 3) Dictionary Mental or Mental or physical exertion.physical exertion.

Scientific Scientific the product of the product of force applied force applied to an object to an object and the and the distance the distance the object moves.object moves.

 

 

4) 3 examples of work4) 3 examples of work

Lifting, Lifting, pushing, pushing, pulling pulling

5) 3 requirements for 5) 3 requirements for work are:work are:

1)1) A A forceforce must be must be applied.applied.

2)2) Object must Object must move.move.

3)3) Motion must be in the Motion must be in the direction of the direction of the forceforce..

Work or Not?Work or Not?

According to the According to the scientific definition, scientific definition, what is work and what is work and what is not?what is not? a teacher lecturing a teacher lecturing

to her classto her class a mouse pushing a a mouse pushing a

piece of cheese piece of cheese with its nose across with its nose across the floorthe floor

Work or Not?Work or Not?

According to the According to the scientific definition, scientific definition, what is work and what is work and what is not?what is not? a teacher lecturing a teacher lecturing

to her classto her class a mouse pushing a a mouse pushing a

piece of cheese piece of cheese with its nose across with its nose across the floorthe floor

What’s work?What’s work? A scientist delivers a speech to an A scientist delivers a speech to an

audience of his peers. audience of his peers. A body builder lifts 350 pounds A body builder lifts 350 pounds

above his head. above his head. A mother carries her baby from room A mother carries her baby from room

to room. to room. A father pushes a baby in a carriage.A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag A woman carries a 20 kg grocery bag

to her car? to her car?

What’s work?What’s work? A scientist delivers a speech to an A scientist delivers a speech to an

audience of his peers. audience of his peers. NoNo A body builder lifts 350 pounds A body builder lifts 350 pounds

above his head. above his head. YesYes A mother carries her baby from room A mother carries her baby from room

to room. to room. NoNo A father pushes a baby in a carriage. A father pushes a baby in a carriage. YesYes A woman carries a 20 km grocery A woman carries a 20 km grocery

bag to her car? bag to her car? NoNo

Formula for workFormula for work

Work = Force x DistanceWork = Force x Distance

The unit of force is newtonsThe unit of force is newtons The unit of distance is metersThe unit of distance is meters The unit of work is newton-metersThe unit of work is newton-meters One newton-meter is equal to one jouleOne newton-meter is equal to one joule So, the unit of work is a So, the unit of work is a joulejoule

W=FDW=FD

Work = Force x Work = Force x DistanceDistance

Calculate: If a man Calculate: If a man pushes a concrete pushes a concrete block 10 meters block 10 meters with a force of 20 with a force of 20 N, how much work N, how much work has he done?has he done?

W=FDW=FD

Work = Force x Work = Force x DistanceDistance

Calculate: If a man Calculate: If a man pushes a concrete pushes a concrete block 10 meters block 10 meters with a force of 20 with a force of 20 N, how much work N, how much work has he done? has he done? 200 200 joulesjoules(W = 20N x 10m)(W = 20N x 10m)

NOT WORK!NOT WORK!

8) How is work 8) How is work calculated?calculated?

Work = force x distanceWork = force x distance W = Fd (W = Fd (draw a triangle)draw a triangle)

The unit is a The unit is a

newton x meternewton x meter = 1 Nm= 1 Nm

A Nm is called a joule (J)A Nm is called a joule (J)

9) James 9) James Prescott JoulePrescott Joule

Foot-pound Foot-pound (ft-lb)(ft-lb)

Torque Torque wrenchwrench

YouYou your friend your friend Mr. Mr. BlueBlue

WE ALL DO THE SAME AMOUNT WE ALL DO THE SAME AMOUNT OF WORK! Every body moves OF WORK! Every body moves one metric ton of dirt 25 meters one metric ton of dirt 25 meters

12) NO! work = F x d 12) NO! work = F x d time does not factor into time does not factor into scientific work.scientific work.

13) POWER13) POWER

15) If you said MR. Blue 15) If you said MR. Blue you are right.you are right.16) Power = work / time16) Power = work / time

P = W / tP = W / tjoule divided by a second joule divided by a second

WATT (W) WATT (W) (J/s or Nm/s)(J/s or Nm/s)

PowerPower Power is the rate at which work is Power is the rate at which work is

done. done.

Power = WorkPower = Work**/Time/Time **(force x distance)(force x distance)

The unit of power is the watt.The unit of power is the watt.

18) James Watt (1736-1819)18) James Watt (1736-1819)19) Improved the steam engine & 19) Improved the steam engine & started the industrial revolutionstarted the industrial revolution

Check for UnderstandingCheck for Understanding1.1.Two physics students, Ben and Bonnie, are Two physics students, Ben and Bonnie, are in the weightlifting room. Bonnie lifts the 50 in the weightlifting room. Bonnie lifts the 50 kg barbell over her head (approximately .60 kg barbell over her head (approximately .60 m) 10 times in one minute; Ben lifts the 50 m) 10 times in one minute; Ben lifts the 50 kg barbell the same distance over his head kg barbell the same distance over his head 10 times in 10 seconds. 10 times in 10 seconds.

Which student does the most work? Which student does the most work?

Which student delivers the most Which student delivers the most power?power?

Explain your answers. Explain your answers.

Ben and Bonnie Ben and Bonnie do the same amount do the same amount of work; they apply of work; they apply the same force to lift the same force to lift the same barbell the the same barbell the same distance above same distance above their heads. their heads.

Yet, Ben is the Yet, Ben is the most powerful since most powerful since he does the same he does the same work in less time. work in less time.

Power and time Power and time are inversely are inversely proportional.proportional.

  

2. How much power will it take to 2. How much power will it take to move a 10 kg mass at an move a 10 kg mass at an acceleration of 2 m/s/s a distance of acceleration of 2 m/s/s a distance of 10 meters in 5 seconds? This 10 meters in 5 seconds? This problem requires you to use the problem requires you to use the formulas for force, work, and power formulas for force, work, and power all in the correct order.all in the correct order.

Force=Mass x Acceleration Force=Mass x Acceleration

Work=Force x DistanceWork=Force x Distance

Power = Work/TimePower = Work/Time

2. How much power will it take to move a 10 kg 2. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s/s a distance of mass at an acceleration of 2 m/s/s a distance of 10 meters in 5 seconds? This problem requires 10 meters in 5 seconds? This problem requires you to use the formulas for force, work, and you to use the formulas for force, work, and power all in the correct order.power all in the correct order.

Force=Mass x Acceleration Force=Mass x Acceleration Force=10 x 2Force=10 x 2Force=20 NForce=20 N

Work=Force x DistanceWork=Force x DistanceWork = 20 x 10Work = 20 x 10

Work = 200 JoulesWork = 200 Joules

Power = Work/TimePower = Work/TimePower = 200/5Power = 200/5

Power = 40 wattsPower = 40 watts

19) Horsepower (hp)19) Horsepower (hp)

20) 1 hp = 746 W20) 1 hp = 746 W

21) Lawnmower engine21) Lawnmower engine

3-100,000 hp3-100,000 hp

A schematic diagram of relaxation oscillator, A schematic diagram of relaxation oscillator, camera motor, hairdryer, power tools, & camera motor, hairdryer, power tools, &

electric train ( nW-MW)electric train ( nW-MW)

23) What is a 23) What is a machine?machine?

Any device that makes work easier.Any device that makes work easier.

24) Machines multiply forces,24) Machines multiply forces,multiply distance ( increase multiply distance ( increase

speed), or speed), or change the direction of the change the direction of the

forceforce25) 25)

26) Work input (W26) Work input (Wii) is the ) is the work you do on the work you do on the machine.machine.

WWii = F = Fefforteffort x d x defforteffort 27) Work output (W27) Work output (Woo) is the ) is the work the machine does on work the machine does on the object or load. the object or load. WWoo = F = Fresistanceresistance x d x dresistanceresistance

28) Efficiency (EFF) & 28) Efficiency (EFF) & Mechanical Advantage Mechanical Advantage (MA)(MA)

Efficiency is the ratio of Efficiency is the ratio of use-ful work output to use-ful work output to neces-sary work input.neces-sary work input.

EFF = WEFF = Woo/W/Wii x 100 = % x 100 = %

Transformer (98%), car (35%), Transformer (98%), car (35%), & human brain (?) & human brain (?)

30) complete the 30) complete the problemproblem31) 31) It depends, friction/soundIt depends, friction/sound

32) Mechanical Advantage (AMA)32) Mechanical Advantage (AMA)

is the number of times forces are is the number of times forces are multiplied.multiplied.

Ideal (theoretical) Mechanical Ideal (theoretical) Mechanical Advantage (IMA) - is the number Advantage (IMA) - is the number of times distances are multipliedof times distances are multiplied

AMA = F AMA = F resistanceresistance / F / F effort

AMA = 10 000 N / 10 N =? IMA = d IMA = d effort / d / d resistanceresistance

IMA = 100 m / 10 m =?

AMA or IMA is unitless AMA or IMA is unitless Note you may use a “x” Note you may use a “x”

like like 100x, 2x, .5x etc100x, 2x, .5x etc

An ideal machine is An ideal machine is friction-less, weightless, friction-less, weightless, massless, and massless, and impossible to build. impossible to build.

A perpetual motion A perpetual motion machine is an machine is an

exampleexample

What makes a machine What makes a machine simple?simple?

34) Stick, rock, club, pre-stone 34) Stick, rock, club, pre-stone age, Africaage, Africa

35) A simple machine does 35) A simple machine does work with one movement.work with one movement.

36) 1) lever36) 1) lever 2) inclined 2) inclined plane plane

3) wheel 3) wheel && axle 4) wedge axle 4) wedge5) pulley5) pulley 6) screw 6) screw

LeverLeverss

Levers are rigid objects that Levers are rigid objects that move at a fulcrum (pivot move at a fulcrum (pivot point) to create MA.point) to create MA.

Classes of Levers - First, Classes of Levers - First, Second and ThirdSecond and Third

Fulcrum is always between Fulcrum is always between the effort & resistancethe effort & resistance

resistance

                                                               

The resistance The resistance is always is always

between the between the fulcrum and fulcrum and

the effortthe effort

                                             

                  

                                                                

                                                               

                                              

                                       

       

                                       

       

                                             

                  

                                             

                   

                                             

                  

                                              

                                             

 

                                              

The effort is The effort is always always

between the between the fulcrum & fulcrum & resistanceresistance

                 

                                          

     

                

                                        

       

                

                              

                 

                             

                 

                             

It is as easy It is as easy asas

1 2 31 2 3

F R EF R E

wheelswheels

Wheel & Wheel & axle is axle is a a rotatinrotating lever.g lever.

pulleyspulleys

Pulleys are ropes, belts, Pulleys are ropes, belts, chains, etc. wrapped chains, etc. wrapped around a wheel & axlearound a wheel & axle

Inclined Plane (IP) a Inclined Plane (IP) a slanted surface used to slanted surface used to lift an object.lift an object.

Wedge are moving IP’s.Wedge are moving IP’s.

Screws are IP’s wrapped Screws are IP’s wrapped around a cylinder. around a cylinder.

Work and Simple Work and Simple MachinesMachines

What is work?What is work?

In science, the word In science, the word workwork has a has a different meaning than you may be different meaning than you may be familiar with.familiar with.

The scientific definition of work is: The scientific definition of work is: using a force to move an object a using a force to move an object a distance (when both the force and distance (when both the force and the motion of the object are in the the motion of the object are in the same direction.)same direction.)