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

Sections for Chapter 4  Section 4.1: pages 67 to 70: Forces in Machines: How do simple machines work?  Section 4.2: pages 71 to 72: The Lever: How does a lever work?  Section 4.3: pages 73 to 76: Designing Gear Machines: How do gears work?

Section 4.1: Forces in Machines pages  Mechanical systems and machines: page 67  Simple machines: page 68  Mechanical advantage: page 69  How a block and tackle works: page 70

Mechanical systems and machines: 4 parts (3 of 4) 1.The world without machines machines 2.What technology allows us to do? 3.What is a machine?  Ten thousands years ago, people lived in a much different world.  Today’s technology allows us to do incredible things.  A machine is a device with moving parts that work together to accomplish a task

Mechanical systems and machines: 4 parts (4 of 4) 4.The concept of input and output  The input includes everything you do to make the machine work, like pushing on the pedals.  The output is what the machine does for you, like going fast.

Quiz for page 67  How does the handbrake on a bike become a simple machine?  Does the handbrake require an input?  Does the handbrake accomplish an output?

Simple machine: 4 parts (2 of 4 parts) 1.The beginning of technology technology 2. Input force and output force  A simple machine is an unpowered mechanical device.  Input force is what you apply and the output force is what the machine applies to the task

Simple machine: 4 parts (2 of 4 parts) 3.The block and tackle 4.Machines within machines Ex: bicycles: wheels & axles, levers and gears Ex: bicycles: wheels & axles, levers and gears  Is another simple machine that uses ropes and pulleys to multiply forces.  Most machines we use today are made up of combinations of different types of simple machines.

Quiz for page 68  What are the input and output forces for a block and tackle?  What are two of the levers on a bicycle?  A motorcycle has the same devices that of a bicycle. Are parts of a motorcycle considered simple machines?

Mechanical advantage: 5 parts ( 2 of 5) 1.Definition of force 2.Units of force  Simple machines work by changing force and motion. Force is an action that has the ability to change motion, like a push or a pull.  Measured in Newtons (N.)

Mechanical advantage: 5 parts ( 1 of 5) 3.Simple machines and force  Simple machines are best understood through the concepts of input and output forces.

Mechanical advantage: 5 parts (1 of 5) 4.Mechanical advantage Figure 4.5 on page 69 The ratio of output force to input force. MA = F MA = F o F i F F o and F i are measured in Newtons (N) MA does not have a unit.

Mechanical advantage: 5 parts (1 of 5) 5.Mechanical engineers People who design machines are mechanical engineers. Machines have a greater output force than input force in order to accomplish the task.

Quiz for page 69  A block and tackle has an input force of 6N and an output force of 18N. What is the mechanical advantage?  What does the result in above problem mean?  What does force have to do with mechanical advantage?

How a block & tackle work: 5 parts (1 of 5) 1.The forces in ropes and strings  Ropes & strings carry tension forces (pulling forces) along their length. Ropes and strings do not carry pushing forces.

How a block & tackle work: 5 parts (1 of 5) 2.Every part of a rope has the same tension If FRICTION is very small, then the force in a rope is the same throughout the rope. Can place a scale anywhere on the rope and get same result throughout.

How a block & tackle work: 5 parts (1 of 5) 3.The forces in a block and tackle Refer to Figure 4.6 page 70  10N weight at the bottom is called a load.  Case A – two upward forces  Case B – three upward forces  Case C – four upward forces

How a block & tackle work: 5 parts (1 of 5) 4.Mechanical advantage  Case C demonstrates that four ropes gives an MA of 4 which means that the output force is four times bigger than the input force.

How a block & tackle work: 5 parts (1 of 5) 5.Multiplying force with the block and tackle Figure 4.6 page 70  If the output is four times more than the input force, the input force can be ¼ of the output force.  Example: 20N of output force means input force can be a minimum of 5N.

United Streaming video for MA of a pulley C:\Documents and Settings\gchong\My Documents\Chapter 4 videos\Calculating_the_Mechanical_Adva ntage_of_a_Pulley.asf C:\Documents and Settings\gchong\My Documents\Chapter 4 videos\Calculating_the_Mechanical_Adva ntage_of_a_Pulley.asf

Quiz page 70  Can the output force be lower then the input force? Why or why not?  A block and tackle has three ropes with 18N of output force. What is the minimum of input force needed?  Why is tension of a rope only pulling action and not a pushing action?

Section 4.2: The Lever pages  What is a lever?: page 71 – Four parts  The mechanical advantage of a lever: page 72 – Four parts

What is a lever? Four parts (2 of 4) 1.Levers are used everywhere 2.Your muscles and skeleton use levers  Levers still form the operating principle behind many common machines. Your bones and muscles work as levers to perform everything from chewing to throwing a ball.

Terms to remember:  Output arm/output force are normally called resistance load or resistance force.  Input arm/input force are normally called effort force.

United Streaming video of lever C:\Documents and Settings\gchong\My Documents\Chapter 4 videos\Lever.asf C:\Documents and Settings\gchong\My Documents\Chapter 4 videos\Lever.asf

What is a lever? Four parts (1 of 4) page 71 3.Parts of a lever a. Definition b.Input arm c. Output arm d. Changing position of fulcrum 3a. A stiff structure (the lever) that rotates around a fixed point called a FULCRUM. 3b.Input arm is the side of lever where the force is applied to the machine. 3c.Output arm is the side of lever where the force is applied by the machine to accomplish a task. 3d.Changing the position of the fulcrum will make a different class of lever.

What is a lever? Four parts (1 of 4) page 71 4.How it works Refer to Figure 4.7 on page 71  If the fulcrum is placed in the middle of the lever, the input and output forces are the same i.e. 100 N of input force makes 100 N of output force.

Mechanical advantage of a lever: 4 parts (1of 4) pg Input and output forces for a lever.  Input force is the force applied to the lever in the area of the input arm.  Output force is the force the machines applies in the area of the output arm.

Mechanical advantage of a lever: 4 parts (1of 4) pg The mechanical advantage of a lever Refer to page 72 Figure 4.8  Another way to say this is that the mechanical advantage of a lever is the ratio of lengths between the input arm and the output arm.

Mechanical advantage of a lever: 4 parts (1of 4) pg The output force can be less than the input force  The input arm is shorter than the output arm.  You might design a lever this way if you needed the motion on the output side to be larger than the motion on the input side.

United Streaming video: Calculating MA of a lever. C:\Documents and Settings\gchong\My Documents\Chapter 4 videos\Calculating_the_Mechanical_Adva ntage_of_a_Lever.asf C:\Documents and Settings\gchong\My Documents\Chapter 4 videos\Calculating_the_Mechanical_Adva ntage_of_a_Lever.asf

Mechanical advantage of a lever: 4 parts (1of 4) pg The three types of levers, as shown in Figure 4.9 page 72  1 st Class Lever – the fulcrum is in middle of input arm and output arm  2 nd Class Lever – the output arm is in the middle of input arm and the fulcrum.  3 rd Class Lever – the input arm is in the middle of the output arm and the fulcrum

United Streaming: Three classes of levers C:\Documents and Settings\gchong\My Documents\Chapter 4 videos\Three_Classes_of_Levers.asf C:\Documents and Settings\gchong\My Documents\Chapter 4 videos\Three_Classes_of_Levers.asf

Examples of Levers 1 st Class Lever 2 nd Class Lever 3 rd Class Lever  Pliers, scissors, screwdriver used to open a paint can, see-saw  Wheel barrow, door  Surfing fishing pole, rake, baseball bat, tennis racket, human arm, tweezers, ice thongs

Quiz for pages 71 to 72 1.________ is the pivot point of a lever. 2.The Classes of levers are decided by what three parts? 3.A woman is sitting eating lunch and fly lands on the table. The woman uses a flyswatter to dispose of the fly. What class of lever is the flyswatter? 4.Using lever to lift a 200N box, what class of lever is used and what would length of the output arm compared to the length of the input arm?

Section 4.3: Designing Gear Machines 1.Science and engineering page parts 2.Gears and rotating machines page 75 5 parts 3.Designing machines page 76 5 parts

Science and engineering: page 73-74: 7 parts (3 of 7) 1.Inventions solve problems 2.What is technology? 3. Science and technology  Most of the inventions came from a practical application of science knowledge.  The application of science to solve problems is called engineering or technology.  Engineers use scientific knowledge to create or improve inventions that solve problems.

Science and engineering: page 73-74: 7 parts (3 of 7) 4.A sample engineering problem 5. The importance of a prototype 6. Testing the prototype  Read page 74  Prototype is a working model of a design that can be tested to see if it works.  The evaluation of test results is a necessary part of any successful design.

Science and engineering: page 73-74: 7 parts (1 of 7) 7. Changing the design and testing again.  The process of design, prototype, test, and evaluate is the engineering cycle (Figure 4.11 pg. 74)

Gears and rotating machines: 5 parts ( of 5) 1.Why are gears used? 2.Gears change force and speed