Chapter 4: Machines & Mechanical Systems Three sections from page 67 to 76

Chapter 4: Machines Chapter 4: Machines & Mechanical & Mechanical SystemsSystems

Three sections from page 67 to 76Three sections from page 67 to 76

Sections for Chapter 4Sections for Chapter 4

Section 4.1: pages 67 to 70: Forces in Section 4.1: pages 67 to 70: Forces in Machines: Machines: How do simple machines How do simple machines work?work?

Section 4.2: pages 71 to 72: The Lever: Section 4.2: pages 71 to 72: The Lever: How does a lever work?How does a lever work?

Section 4.3: pages 73 to 76: Designing Section 4.3: pages 73 to 76: Designing Gear Machines: Gear Machines: How do gears work?How do gears work?

Section 4.1: Forces in Section 4.1: Forces in Machines pages 67-70Machines pages 67-70

Mechanical systems and machines: page Mechanical systems and machines: page 6767

Simple machines: page 68Simple machines: page 68 Mechanical advantage: page 69Mechanical advantage: page 69 How a block and tackle works: page 70How a block and tackle works: page 70

Mechanical systems and Mechanical systems and machines: 4 parts (3 of 4)machines: 4 parts (3 of 4)

1.1. The world without The world without machinesmachines

2.2. What technology What technology allows us to do?allows us to do?

3.3. What is a machine?What is a machine?

Ten thousands years Ten thousands years ago, people lived in a ago, people lived in a much different world.much different world.

Today’s technology Today’s technology allows us to do allows us to do incredible things.incredible things.

A machine is a A machine is a device with moving device with moving parts that work parts that work together to together to accomplish a taskaccomplish a task

Mechanical systems and Mechanical systems and machines: 4 parts (4 of 4)machines: 4 parts (4 of 4)

4.4. The concept of The concept of inputinput and and outputoutput

The The input input includes includes everything you do to everything you do to make the machine make the machine work, like pushing on work, like pushing on the pedals.the pedals.

The The outputoutput is what is what the machine does for the machine does for you, like going fast.you, like going fast.

Quiz for page 67Quiz for page 67

How does the handbrake on a bike How does the handbrake on a bike become a simple machine?become a simple machine?

Does the handbrake require an Does the handbrake require an inputinput??

Does the handbrake accomplish an Does the handbrake accomplish an outputoutput??

Simple machine: 4 parts Simple machine: 4 parts (2 of 4 parts)(2 of 4 parts)

1.1. The beginning of The beginning of

technologytechnology

2. Input force and 2. Input force and output forceoutput force

A simple machine is A simple machine is an an unpoweredunpowered mechanical device.mechanical device.

Input forceInput force is what is what you apply and the you apply and the output forceoutput force is what is what the machine applies the machine applies to the taskto the task

Simple machine: 4 parts Simple machine: 4 parts (2 of 4 parts)(2 of 4 parts)

3.3. The block and The block and tackletackle

4.4. Machines within Machines within machinesmachines

Ex: bicycles: wheels Ex: bicycles: wheels & axles, levers and & axles, levers and gearsgears

Is another simple Is another simple machine that uses machine that uses ropes and pulleys to ropes and pulleys to multiply forces.multiply forces.

Most machines we Most machines we use today are made use today are made up of combinations of up of combinations of different types of different types of simple machines.simple machines.

Quiz for page 68Quiz for page 68

What are the What are the input and output forcesinput and output forces for for a block and tackle?a block and tackle?

What are two of the What are two of the levers levers on a bicycle?on a bicycle?

A motorcycle has the same devices that A motorcycle has the same devices that of a bicycle. Are parts of a motorcycle of a bicycle. Are parts of a motorcycle considered simple machines?considered simple machines?

Mechanical advantage: 5 Mechanical advantage: 5 parts ( 2 of 5)parts ( 2 of 5)

1.1. Definition of Definition of forceforce

2.2. Units of forceUnits of force

Simple machines Simple machines work by changing work by changing force and motion. force and motion. ForceForce is an action is an action that has the ability to that has the ability to change motion, like a change motion, like a push or a pull.push or a pull.

Measured in Measured in Newtons (N.)Newtons (N.)

Mechanical advantage: 5 Mechanical advantage: 5 parts ( 1 of 5)parts ( 1 of 5)

3.3. Simple machines Simple machines and forceand force

Simple machines are Simple machines are best understood best understood through the concepts through the concepts of input and output of input and output forces.forces.

Mechanical advantage: 5 Mechanical advantage: 5 parts (1 of 5)parts (1 of 5)

4.4. Mechanical Mechanical advantageadvantage

Figure 4.5 on Figure 4.5 on page 69page 69

The ratio of output force to The ratio of output force to input force.input force.

MA = MA = FFo

Fi

FFo and Fi are measured in Newtons (N)

MA does not have a unit.

Mechanical advantage: 5 Mechanical advantage: 5 parts (1 of 5)parts (1 of 5)

5.5. Mechanical Mechanical engineersengineers

People who design People who design machines are machines are mechanical mechanical engineers.engineers.

Machines have a Machines have a greater output force greater output force than input force in than input force in order to accomplish order to accomplish the task.the task.

Quiz for page 69Quiz for page 69 A block and tackle has an input force of 6N A block and tackle has an input force of 6N

and an output force of 18N. What is the and an output force of 18N. What is the mechanical advantage?mechanical advantage?

What does the result in above problem What does the result in above problem mean?mean?

What does force have to do with mechanical What does force have to do with mechanical advantage?advantage?

How a block & tackle How a block & tackle work: 5 parts (1 of 5)work: 5 parts (1 of 5)

1.1. The forces in The forces in ropes and ropes and

stringsstrings

Ropes & strings carry Ropes & strings carry tension forces tension forces (pulling forces) along (pulling forces) along their length. their length. Ropes Ropes and strings do and strings do notnot carry pushing forcescarry pushing forces..


2.2. Every part of a rope Every part of a rope has the same tensionhas the same tension

If FRICTION is very If FRICTION is very small, then the force small, then the force in a rope is the same in a rope is the same throughout the rope. throughout the rope. Can place a scale Can place a scale anywhere on the anywhere on the rope and get same rope and get same result throughout.result throughout.


3.3. The forces in a The forces in a block and block and tackletackle

Refer to Figure Refer to Figure 4.6 page 704.6 page 70

10N weight at the bottom 10N weight at the bottom is called a is called a loadload..

Case A – two upward Case A – two upward forcesforces

Case B – three upward Case B – three upward forcesforces

Case C – four upward Case C – four upward forcesforces


4.4. Mechanical Mechanical advantageadvantage

Case C Case C demonstrates that demonstrates that four ropes gives an four ropes gives an MA of 4 which means MA of 4 which means that the output force that the output force is four times bigger is four times bigger than the input force.than the input force.


5.5. Multiplying Multiplying force with the force with the block and tackleblock and tackle

Figure 4.6 page Figure 4.6 page 7070

If the output is four times If the output is four times more than the input more than the input force, the input force force, the input force can be ¼ of the output can be ¼ of the output force.force.

Example: 20N of output Example: 20N of output force means input force force means input force can be a minimum of 5N.can be a minimum of 5N.

United Streaming United Streaming video for MA of a video for MA of a pulleypulley

C:\Documents and Settings\C:\Documents and Settings\gchonggchong\My Documents\Chapter 4 videos\\My Documents\Chapter 4 videos\Calculating_the_Mechanical_Advantage_Calculating_the_Mechanical_Advantage_of_a_Pulley.asfof_a_Pulley.asf

Quiz page 70Quiz page 70

Can the output force be lower then the input Can the output force be lower then the input force? Why or why not?force? Why or why not?

A block and tackle has three ropes with 18N A block and tackle has three ropes with 18N of output force. What is the minimum of of output force. What is the minimum of input force needed?input force needed?

Why is tension of a rope only pulling action Why is tension of a rope only pulling action and not a pushing action?and not a pushing action?

Section 4.2: The Section 4.2: The Lever pages 71-72Lever pages 71-72 What is a lever?: page 71 – Four What is a lever?: page 71 – Four

partsparts

The mechanical advantage of a The mechanical advantage of a lever: page 72 – Four partslever: page 72 – Four parts

What is a lever? Four What is a lever? Four parts (2 of 4)parts (2 of 4)

1.1. Levers are used Levers are used everywhereeverywhere

2.2. Your muscles and Your muscles and skeleton use leversskeleton use levers

Levers still form the Levers still form the operating principle operating principle behind many common behind many common machines.machines.

Your bones and muscles Your bones and muscles work as levers to work as levers to perform everything from perform everything from chewing to throwing a chewing to throwing a ball.ball.

Terms to remember:Terms to remember:

Output arm/output force are Output arm/output force are normally called normally called resistance load or resistance load or resistance forceresistance force..

Input arm/input force are normally Input arm/input force are normally called called effort forceeffort force..

United Streaming United Streaming video of levervideo of leverC:\Documents and Settings\C:\Documents and Settings\gchonggchong\My Documents\Chapter 4 videos\\My Documents\Chapter 4 videos\Lever.asfLever.asf

What is a lever? Four What is a lever? Four parts (1 of 4) page 71parts (1 of 4) page 71

3.3. Parts of a leverParts of a lever

a. Definitiona. Definition

b.b. Input armInput arm

c. Output armc. Output arm

d. Changing d. Changing position position

of of fulcrumfulcrum

3a3a. . A stiff structure (the lever) that A stiff structure (the lever) that rotates rotates around a fixed point around a fixed point called a called a FULCRUMFULCRUM..

3b.3b. Input armInput arm is the side of lever is the side of lever where the force is applied to the where the force is applied to the machine.machine.

3c.3c. Output armOutput arm is the side of lever is the side of lever where the force is applied by the where the force is applied by the machine to accomplish a task.machine to accomplish a task.

3d3d .. Changing the position of the Changing the position of the fulcrum will make a different class fulcrum will make a different class of lever.of lever.

What is a lever? Four What is a lever? Four parts (1 of 4) page 71parts (1 of 4) page 71

4.4. How it worksHow it works

Refer to Figure 4.7 Refer to Figure 4.7 on page 71on page 71

If the fulcrum is If the fulcrum is placed in the middle placed in the middle of the lever, the input of the lever, the input and output forces are and output forces are the same i.e. 100 N the same i.e. 100 N of input force makes of input force makes 100 N of output 100 N of output force.force.

Mechanical advantage of a Mechanical advantage of a lever: 4 parts (1of 4) pg. lever: 4 parts (1of 4) pg. 7272

1.1. Input and output Input and output forces for a lever.forces for a lever.

Input forceInput force is the is the force applied to the force applied to the lever in the area of lever in the area of the input arm.the input arm.

Output forceOutput force is the is the force the machines force the machines applies in the area of applies in the area of the output arm.the output arm.

Mechanical advantage of a Mechanical advantage of a lever: 4 parts (1of 4) pg. 72lever: 4 parts (1of 4) pg. 72

2.2. The mechanical The mechanical advantage of a advantage of a leverlever

Refer to page 72 Refer to page 72 Figure 4.8Figure 4.8

Another way to say Another way to say this is that the this is that the mechanical mechanical advantage of a lever advantage of a lever is the ratio of lengths is the ratio of lengths between the input between the input arm and the output arm and the output arm.arm.


3. The output force 3. The output force can be less than can be less than the input forcethe input force

The input arm is shorter The input arm is shorter than the output arm.than the output arm.

You might design a lever You might design a lever this way if you needed the this way if you needed the motion on the output side to motion on the output side to be larger than the motion be larger than the motion on the input side.on the input side.

United Streaming video: United Streaming video: Calculating MA of a Calculating MA of a lever.lever.

C:\Documents and Settings\C:\Documents and Settings\gchonggchong\My Documents\Chapter 4 videos\\My Documents\Chapter 4 videos\Calculating_the_Mechanical_Advantage_Calculating_the_Mechanical_Advantage_of_a_Lever.asfof_a_Lever.asf


4.4. The three types of The three types of levers, as shown in levers, as shown in Figure 4.9 page 72Figure 4.9 page 72

11stst Class Lever – the Class Lever – the fulcrumfulcrum is in middle is in middle of input arm and of input arm and output armoutput arm

22ndnd Class Lever – the Class Lever – the output arm is in the output arm is in the middle of input arm middle of input arm and the and the fulcrumfulcrum..

33rdrd Class Lever – the Class Lever – the input arm is in the input arm is in the middle of the output middle of the output arm and the arm and the fulcrumfulcrum

United Streaming: United Streaming: Three classes of leversThree classes of levers

C:\Documents and Settings\C:\Documents and Settings\gchonggchong\My Documents\Chapter 4 videos\\My Documents\Chapter 4 videos\Three_Classes_of_Levers.asfThree_Classes_of_Levers.asf

Examples of LeversExamples of Levers

11stst Class Lever Class Lever

22ndndClass LeverClass Lever

33rdrd Class Lever Class Lever

Pliers, scissors, screwdriver Pliers, scissors, screwdriver used to open a paint can, used to open a paint can, see-sawsee-saw

Wheel barrow, doorWheel barrow, door

Surfing fishing pole, rake, Surfing fishing pole, rake, baseball bat, tennis racket, baseball bat, tennis racket, human arm, tweezers, ice human arm, tweezers, ice thongsthongs

Quiz for pages 71 to 72Quiz for pages 71 to 721.1. ________ is the pivot point of a lever.________ is the pivot point of a lever.

2.2. The Classes of levers are decided by what three The Classes of levers are decided by what three parts?parts?

3.3. A woman is sitting eating lunch and fly lands on A woman is sitting eating lunch and fly lands on the table. The woman uses a flyswatter to the table. The woman uses a flyswatter to dispose of the fly. What class of lever is the dispose of the fly. What class of lever is the flyswatter?flyswatter?

4.4. Using lever to lift a 200N box, what class of lever Using lever to lift a 200N box, what class of lever is used and what would length of the output arm is used and what would length of the output arm compared to the length of the input arm?compared to the length of the input arm?

Section 4.3: Designing Section 4.3: Designing Gear MachinesGear Machines

1.Science and engineering page 73-74 1.Science and engineering page 73-74

7 parts7 parts

2.Gears and rotating machines page 752.Gears and rotating machines page 75

5 parts5 parts

3.Designing machines page 763.Designing machines page 76

5 parts5 parts

Science and engineering: Science and engineering: page 73-74: 7 parts (3 of 7)page 73-74: 7 parts (3 of 7)

1.Inventions 1.Inventions solve problemssolve problems

2.What is 2.What is technology?technology?

3. Science and 3. Science and technologytechnology

Most of the inventions came from a Most of the inventions came from a practical application of science practical application of science knowledge.knowledge.

The application of science to solve The application of science to solve problems is called problems is called engineeringengineering or or technology.technology.

Engineers use scientific knowledge to Engineers use scientific knowledge to create or improve inventions that solve create or improve inventions that solve problems.problems.


4.A sample engineering 4.A sample engineering problemproblem

5. The importance of a 5. The importance of a prototypeprototype

6. Testing the 6. Testing the prototypeprototype

Read page 74Read page 74

Prototype is a working Prototype is a working model of a design that model of a design that can be tested to see if can be tested to see if it works.it works.

The evaluation of test The evaluation of test results is a necessary results is a necessary part of any successful part of any successful design.design.


7. Changing the 7. Changing the design and testing design and testing again.again.

The process of The process of design, prototype, design, prototype, test, and evaluate is test, and evaluate is the the engineering engineering cyclecycle (Figure 4.11 (Figure 4.11 pg. 74)pg. 74)

Gears and rotating Gears and rotating machines: 5 parts ( of 5)machines: 5 parts ( of 5)

1.1. Why are gears Why are gears used?used?

2.2. Gears change force Gears change force and speedand speed