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

Chapter 14.1 F d

Work Work Requires Motion  The force must act in the same direction that the object moves. If there is no movement, no work is done.

Work depends on direction!!

Work depends on direction!! No Work!!

Work depends on direction!!

Work = Force X distance W = F X d W = Newton X meter = N·m W = Joule (J)

Fd W = W W d F = F d W F d =

Power Work Time Power = P = t W

Pt W = W W t P = P t W P t =

Increase work done in same time. Same amount of work in less time. Increase Power Increase work done in same time. Same amount of work in less time.

Power Joules seconds = Watts Power = s J P = = W

Example You exert a vertical force of 72 N to lift a box to a height of 1.0 m in a time of 2.0 s. How much power is used to lift the box?

P = 36 J/s = 36 W Given: F =72 N d=1.0 m t = 2.0s Find: P =? Equation: P = W/t w = Fd P = Fd/t Solve: P = (72N x 1.0m)/2.0s P = 36 J/s = 36 W

James Watt - Horsepower 1 horsepower is equal to 746 watts

Homework Worksheet: 14-1 Due: 4/5/10

Chapter 14.2 Work = Force X distance Machines Can machines decrease work??? Work = Force X distance

Machines do Work

Machines do Work Work = Force X distance Machines make work easier to do. Work = Force X distance Change the size of a force needed The direction of a force. The distance over which a force acts.

Increasing Force

Direction of Force

Distance the force acts.

Work Input and Work Output

Work Input and Work Output

Work Input and Work Output Because of friction, the work done by a machine (output work) is always less than the work done on the machine (input work).

Work Input to a machine The force you exert on a machine is called the input force. The distance the input force acts through is known as the input distance

Work Input to a machine

Work Output from a machine The force exerted by a machine is called the output force. The distance the output force acts through is known as the output distance.

Work Output from a machine

Homework Worksheet: 14-1 Worksheet: 14-2 Due: 4/5/10

Chapter: 14-3 Mechanical Advantage And Efficiency

Actual Mechanical Advantage Actual Mechanical Advantage (MA) The number of times a machine multiplies the Input Force.

Actual Mechanical Advantage FI FO

Input Force - FI Output Force - FO

Actual Mechanical Advantage MA = Output Force Input force MA = FO FI

Experiment

Ideal Mechanical Advantage (IMA) IMA of a machine is the mechanical advantage in the absence of friction.

Ideal Mechanical Advantage DI Do

Ideal Mechanical Advantage - IMA IMA = Input Distance Output Distance MA = DI DO

Experiment

MA Example Example: Mr. Clune is trying to move a large stone in his yard. He uses a crow bar that gives him a Mechanical Advantage of 100. If the stone weighs 1000N, what force must Mr. Clune apply to move it?

Fe = 10N Find: Fe = ? Equation: Fe = Fr MA Solve: Fe = 1000N 100 Given: MA = 100 Fr = 1000N Find: Fe = ? Equation: Fe = Fr MA Solve: Fe = 1000N 100 Fe = 10N

Efficiency The measure of how much work put into a machine is changed to useful work put out by the machine Work Input (WIN) Work Output (WOUT)

WOUT WIN Efficiency = X 100% Fo • Do FI • DI Efficiency = X 100%

Experiment

Example: A sofa weighing must be placed in a truck bed off the ground. A worker uses a force of to push the sofa up an inclined plane that has a slope length of What is the of the inclined plane? 1500N 1.0m 500N 4.0m. efficiency

Fo = 1500N FI = 500N l = 4m (DI) h = 1m (Do)

Efficiency = 75% Given: Fo = 1500N Do = 1.0m FI = 500N DI = 4.0m Find: Efficiency = ? FI • DI Fo • Do Equation: Efficiency = X100% Solve: Eff. = X100% 1500N•1.0m 500N•4.0m Efficiency = 75%

Worksheet: 14-3 Math Practice: Page: 425 1-3 Page: 426 8-9 Due: 4/7/10 Homework Worksheet: 14-3 Math Practice: Page: 425 1-3 Page: 426 8-9 Due: 4/7/10

A student working in a grocery store after school pushes several grocery carts together along a ramp. The ramp is 3 meters long and rises 0.5 meter. What is the ideal mechanical advantage of the ramp?

A construction worker moves a crowbar through a distance of 0 A construction worker moves a crowbar through a distance of 0.50 m to lift a load 0.05 m off of the ground. What is the IMA of the crowbar?

The IMA of a simple machine is 2.5. If the output distance of the machine is 1.0 m, what is the input distance?

You have just designed a machine that uses 1000 J of work from a motor for every 800 J of useful work the machine supplies. What is the efficiency of your machine?      

If a machine has an efficiency of 40%, and you do 1000 J of work on the machine, what will be the work output of the machine?

Lever

Wheel and Axle

Pulley

Inclined Plane

Screw

Wedge

Work Work In = Work Out Work = Force · Distance

FI Do DI Fo

Wout = Win   Fo x Do = FI x DI  

Example: If the stone has to be moved to 0. 1m high, how far does Mr Example: If the stone has to be moved to 0.1m high, how far does Mr. Clune have to apply his force. Given: Fo = 1000N Find: de = ? dr = 0.1m Fe = 10N Equation: de = ( Fr x dr ) / Fe = ( 1000N x 0.1m ) / 10N de = 10m

Ideal Mechanical Advantage IMA Ideal Machine – A machine in which the work input equals work output. Win = Wout

A bar that is free to pivot The Lever A bar that is free to pivot about a fixed point.. Fi Fo Di Do Fulcrum..

Do IMA for the Lever IMAlever = input arm length output arm length IMAlever = Di Do

Given: Do = 0.50cm Find: IMA Di = 20cm Equation: MA = Di Do Example: A screwdriver is used to pry open the lid of a paint can. The output arm is 0.50cm long. The input arm is 20cm long. What is the mechanical advantage of the screwdriver? Given: Do = 0.50cm Find: IMA Di = 20cm Equation: MA = Di Do Solve: IMA = 20 cm 0.50cm IMA = 40

Classes of Levers First Class O I O I Second Class O I Third Class

Wheel and Axle A wheel and axle is a simple machine consisting of two wheels of different sizes that rotate together.

Wheel and Axle

No Power Steering!!

Wheel and Axle ra rw

rw ra IMAWheel&Axle= rw ra IMA of a Wheel and Axle IMA = radius of wheel radius of axle rw ra rw ra IMAWheel&Axle=

Solve: IMA = 20cm 2cm IMA = 10 Given: rw = 20cm Find: IMA = ? ra = 2cm Example: An antique car, with no power steering, has a steering wheel with a radius of 20cm. The wheel turns an axle that has a radius of 2cm. What is the Mechanical Advantage of this wheel and axle system? Given: rw = 20cm Find: IMA = ? ra = 2cm Equation: IMA = rw ra Solve: IMA = 20cm 2cm IMA = 10

A slanted surface used to raise objects Inclined Plane A slanted surface used to raise objects

IMA of an Inclined Plane h l h IMA Inclined Plane =

Example: A piano must be raised from the ground to the first floor, a distance of 0.5m. A 10m plank is used to help to movers pick the piano up. If the piano weighs 3000N, what force do the movers have to apply to the piano?

l = 10m Fo = 3000N h = .5m

Find: IMA = ? Fi = ? Given: length ( l ) = 10m height ( h ) = 0.5m Fo = 3000N Find: IMA = ? Fi = ?

Equation: IMA = l h Solve IMA = 10m 0.5m IMA = 20 Equation: Fi = Fo MA Solve Fi = 3000N 20 Fi = 150N

An inclined plane with either one or two sloping sides. Wedge An inclined plane with either one or two sloping sides. More IMA

IMAScrew – Number of Threads An inclined plane wound around a cylinder. More IMA IMAScrew – Number of Threads

Pulleys Fixed Pulley Movable Pulley

Fixed Pulleys

Fixed Pulleys Fixed Pulley I O I 1st Class Lever O

Movable Pulleys

Movable Pulleys R E 2nd Class Lever I Movable Pulley O

Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight. 30N 30N 30N IMA = 1

Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight. 15N 15N 15N 30N IMA = 2

Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight. 10N 10N 10N 10N 30N IMA = 3

The arrangement of several pulleys. Block and Tackle The arrangement of several pulleys.

A machine made by combining two or more simple machines together. Compound Machine A machine made by combining two or more simple machines together. Yo

Packet 14-4 Word Wise & Math Due: 4/13/10 Homework 14-4 Packet 14-4 Word Wise & Math Due: 4/13/10 Test: 4/15/10

The science of designing artificial replacements for parts Mending with Machines Bionics The science of designing artificial replacements for parts of the human body

Artificial replacements for human limbs. Prostheses Artificial replacements for human limbs.

Functional Neuromuscular Stimulation FNS Brain Touch Sensors Receiver Transmitter

Homework 7-4 Section Wrap-Up Page: 197 Due 01/7/05

Power is the rate at which work is done. Power = work time P = F • d t

Example : A figure skater lifts his partner, who weighs 450N, 1 Example : A figure skater lifts his partner, who weighs 450N, 1.0m in 3.0s. How much power is required. d = 1m t = 3s

P = 150W Given: F = 450N d = 1.0m t = 3.0s Find: Power F • d t Equation: P = F • d t 450N • 1.0m 3.0s Solve: P = P = 150W