W O R K&S I M P L EM A C H I N E S

The right tool for the right job.

W O R K

• Work is defined as a force applied over a distance.

• W = F • d• Work in Joules (N•m) = Force in

Newtons (N) • distance in meters (m)

• NOTE: If the object does not move in the direction of the force, NO WORK IS ACCOMPLISHED.

How much work is accomplished by moving a 600N crate 7 m?

1. 85.7 J2. 0.012 J3. 4200 J4. 593 J5. 607 J6. 657979.9 J

How much work is accomplished by a 4500N piledriver falling 25 m?

1. 180 J2. 112500 J3. 0.005 J4. 4475 J5. 4525 J6. 3.2 x 1014 J

How far do you have to push a 300 N crate toaccomplish 6000 J of work?1. 1800000 m2. 0.05 m3. 20 m4. 5700 m5. 6300 m

Which of these unit combinations represents one Joule of work?

1. kg●m2. kg●m/s2

3. N●m/s2

4. kg●m2

5. N●m6. kg 2 ●m/s2

How much work is accomplished by an 80kg person walking 10 m upstairs?1. 800 J2. 8 J3. 0.125 J4. 7840 J5. 70 J6. 90 J

M A C H I N E S

• Machines are devices that help us accomplish work. They can do this by:– Redirecting a force– Multiplying a force– Both redirecting & multiplying a force

W O R K on M A C H I N E S• The force you put into a machine is the

Input or Effort Force (Fe or Fi).

• The distance the machine moves because of the Effort Force is the Effort Distance (de).

• The Effort Force multiplied by the Effort Distance gives you the Work Input (WIN) for the machine.

Fe ● de = WIN

W O R K on M A C H I N E S

• The force the machine applies to another object is the Output or Resistance Force (Fr or Fo).

• The distance the machine moves the other object because of the Resistance Force is the Resistance Distance (dr).

• The Resistance Force multiplied by the Resistance Distance gives you the Work Output (WOUT) for the machine.

Fr ● dr = WOUT

T R A D E – O F F

• In normal operations, – the person using the machine moves the

machine with little force (Fe) through a large distance (de).

– The machine moves an object with a large force (Fr) over a small distance (dr).

• In essence, you are moving the machine an extra distance so the machine will apply extra force.

Which force do you supply to a machine?

1. Effort Force

2. Effort Distance

3. Input Force

4. Resistance Force

5. Resistance Distance

6. Output Force

How far does the machine move another object?

1. Effort Force

2. Effort Distance

3. Input Force

4. Resistance Force

5. Resistance Distance

6. Output Force

Which components comprise the Work Output?

1. Effort Force

2. Effort Distance

3. Resistance Force

4. Resistance Distance

Which of these do you increase on a machine?

1. Effort Force

2. Effort Distance

3. Resistance Force

4. Resistance Distance

Which of these does the machine increase?

1. Effort Force

2. Effort Distance

3. Resistance Force

4. Resistance Distance

Mechanical Advantage

• Mechanical Advantage describes the number of times a machine multiplies the force you apply to it.

MA = Fo/ Fi

What is the mechanical advantage of a machine that applies 35 N for the 25 N of force put into it?0%

0%

0%

0%

0%

1. 8752. 0.73. 1.44. -105. 10

What is the MA of a machine that applies 100 N for the 15 N of force put into it?0%

0%

0%

0%

0%

1. 0.152. 6.73. 15004. -855. 85

What is the Force Output of a machine with a MA of 12 when you put 9 N of force into it?0%

0%

0%

0%

0%

1. 21 N2. -3 N3. 1.3 N4. 0.75 N5. 108 N

Simple Machines

• A Simple Machine accomplishes the work in one motion.

• A Compound Machine is made up of two or more simple machines. Most machines are compound machines.

The Lever• A Lever is comprised of a bar that moves

around a fixed point. The fixed point, or pivot point, is called the fulcrum. – The distance from where the effort force is

applied to the fulcrum is the Effort Arm of the lever.

– The distance from the fulcrum to where the resistance force is applied is the Resistance Arm.

MALEVER

• The MA of a lever is calculated as:MALever = Effort Arm

Resistance Arm

(both in units of length, so there are no MA units)

The longer the effort arm, the more the MA

1st Class Lever

• See-Saw (Teeter-Totter)

• Prying up a lid by pushing down on a bar

• Pairs: Scissors, Pliers, Hedgeclippers

2nd Class Lever

• Door• Wheelbarrow• Pairs: Shears,

Nutcracker

3rd Class Lever

• WARNING: MA < 1• Increases

distance, not force• Anything you

swing– Bat, sword, stick,

golf club

• Brooms, rakes, mops

What is the MA of a lever with an Effort Arm of 6 m and a Resistance Arm of .3 m?

1. 2

2. .2

3. 1.8

4. 0.05

5. 20

6. 200

Which type of lever does not increase the force output of the machine?

0%

0%

0%

0%

1. 1st class2. 2nd class3. 3rd class4. 4th class

If a lever has a MA of 9, and a force of 6 N is applied, how much force will the lever apply?

1. 0.67 N

2. 1.5 N

3. 54 N

Wheel-and-Axle

• A simple machine made of two circles of different diameters that rotate together.

• The outer circle (wheel) is turned with less force over a larger distance so that the inner circle (axle) turns with more force over a shorter distance.

MAWheel-and-Axle

• MA = rWheel

rAxle

Explains how to steer larger vehicles with less force

Ex. Steering wheels, door knobs, faucet handles

What is the MA of a Wheel with a 50 cm radius connected to an Axle with a 2.5 cm radius?

1. 125

2. 20

3. 0.05

Pulley• The Pulley is a

simple machine comprised of a wheel with a rope or chain running around it.

• The MA of a pulley system is equal to the number of supporting ropes.

2 Types of Pulleys

• There are two kinds of pulleys, fixed and moveable.

• Fixed pulleys do not move, and only redirect force.

• Moveable pulleys are attached to the object being moved and multiply force.

The Block-and-Tackle

• A Block and Tackle system is a multiple-pulley system where large amounts of distance are converted into force.

What is the MA of this pulley system?

1. 1

2. 2

3. 3

4. 4

5. 5

6. 6

7. 7

8. 8

9. 9

10. 10

What is the Force Output of this pulley system?

1. 10 N

2. 100 N

3. 50 N

4. 500 N

5. 5000N

Inclined Plane• The Inclined Plane

is a sloping surface used to lift objects.

• It is easier to apply a small force over the slope of the ramp than to lift the object straight up the height of the ramp.

What is the MA of a ramp that is 12 m long but only 4 m tall?

0%

0%

0%

0%

1. 482. 0.333. 34. 8

The Wedge

• The Wedge is comprised of a moving inclined plane or two or more inclined planes put back-to-back.

The Screw

• A Screw is an inclined plane wrapped around a cylinder.

• MA is increased by increasing the pitch (slope) of the threads or the number of threads per unit length.

More on the screw

• A screw works when a material is pushed up the inclined plane formed by the threads

• As more material is in contact with the threads, the overall amount of friction increases

• Screws pull objects together (apart) and can hold more force than a nail of equal size

2 Types of Simple Machines?

• In essence, the pulley and the wheel-and-axle are types of levers

• The wedge and screw are types of inclined planes

What is the function of an inclined plane?

1. Slide objects2. Raise objects up3. Transport

objects over a long distance

What is the MA of an inclined plane with a height of 3 m and a length of 6 m?1. 32. 203. 0.54. 95. 2

Which type of pulley multiplies force?

1. Fixed2. Taffy3. Moveable4. Shank

What is the MA of a handle with a diameter of 9 cm if the post has a diameter of 3 cm?1. 272. 123. 64. 35. 0.333

Which of these is an example of a lever?1. Inclined Plane2. Pulley3. Wedge4. Screw5. Knife edge6. Bolt

Which of these is an example of an inclined plane?1. Wheel-and-Axle2. Pulley3. 2nd Class lever4. Wedge5. Bicycle

Efficiency

• Describes how well machine converts the energy put into it

• Always shown as a percentage

• 100% efficient means that all of the energy put into the machine is applied to the object being worked on

2nd Law of Thermodynamics

• States that whenever energy is converted from one form to another, some energy is always lost as heat due to friction

no machine can be 100% efficient (an “Ideal Machine”)

Efficiency Formula

• WOUTPUT = Fr x dr

• WINPUT = Fe x de

• If you wind up with an answer at If you wind up with an answer at

more than 100%, you have your more than 100%, you have your

fraction upside-downfraction upside-down

X 100%

Converting percentages

• A whole number becomes a decimal out of 100

48% = 0.48 6% = 0.06• A decimal becomes a whole

number, adding the percentage sign

0.21 = 21% 0.75 = 75%

What is the efficiency of a machine that produces 89 J of work for the 100 J of work put into it?0%

0%

0%

0%

0%

1. 8900 J2 2. 1.123. 0.894. 112%5. 89%

What is the efficiency of a machine that produces 6100 J of work for the 9000 J of work put into it?0%

0%

0%

0%

0%

1. 1.48 2. 68%3. 148%4. 0.6775. 54900000 J2

What is the Work Output of a 62% efficient machine when 1000 J of work is put into it?

0%

0%

0%

0%

0%

1. 0.62 J2. 16.13 J3. 620 J4. 1612.9 J5. 62000 J

How much work must be put into a 21% efficient machine to generate 34 J of useable work?0%

0%

0%

0%

1. 7.14 J2. 161.9 J3. 714 J4. 1.619 J

P O W E R

• Power is the rate at which work is accomplished

P = W t W

P t

Power – Power – Power

• Power is measured in Joules per second, called Watts (W)

• For the same amount of work, less time requires more power

How much power applies 600 J of work in 9s?

1. 66.7 W2. 5400 W3. 0.015 W

Applying 21000 W of power produces how much work in 7 s?

1. 3000 J2. 0.0003 J3. 147000 J