Mechanical Systems

Machines are tools that help humans do work

Machines help people use energy more effectively.

Machine :

A device that helps us to do work.

An example of technology developing is a combine harvester.


Simple Machines – Meet Human Needs

Early machines

1)    Were very simple devices

2)    Depended on people & animals for their source of energy.

3)    Example: Plow


   How did earlier civilizations get water to their homes?

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(I) Roman Aqueducts

Used for transporting water for many kilometres to supply cities.

Had 3 parts:  Pump – raise water into reservoirs.

                     Channels – on a slope to carry the water.

                     Distribution system – distributes water within a city.

 

(II) Sakia (Persian wheel)

  • Series of buckets attached to a long rope, draped over a wheel.
  • Wheel is turned by animals which raises the buckets of water.
  • After water is raised it is stored in tanks.
  • Gravity moves water through pipes and into homes.

(III) Archimedes Screw

  • A screw picks up the water and carries it up to the top of the tube.
  • Originally powered by hand, then later by gas or electric motors.
  • Leonardo da Vinci later used 2 Archimedes screws to increase efficiency

(IV) Present Day

  • Pumps keep the water flowing and are powered by motors.

Simple Machines

Simple Machine:

A tool or device made up of one basic machine.

  • There are 6 simple machines that help us do work.
  • Each machine has its own advantages and disadvantages.
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1)  Lever:

A rigid bar or plank that can rotate around a fixed point called a pivot or fulcrum.

Enables the user to move a larger load than without.

But the user must move a greater distance than the load.

3 types:

            Determined by the location of the fulcrum and the load being moved.

(I) First class lever – fulcrum between the load and the point of effort.

(II) Second class lever – load is between the effort and the fulcrum.

(III) Third class lever – has the effort between the load and the fulcrum.

 

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2) Inclined Plane:

A flat surface that is at an angle to another flat surface, such as the ground.

  • Enables the user to move a larger load than without.
  • But the user must move a greater distance than the load.
  • The ramp cannot be too steep in order to work.
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3)Wedge:

Similar to an inclined plane, but is forced into an object.

  • By pressing on the wide end, the narrow end splits the object.
  • Can only be used in one direction, to push objects apart.
  • Enables the user to apply a greater force on an object.
  • But the user must move a greater distance than the split.
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4)Screw:

Consists of a cylinder with a groove cut in a spiral on the outside.

  • Can penetrate materials using a relatively small force.
  • Convert rotational motion to linear motion.
  • Most screws move objects very slowly.
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5)Pulley:

Made up of a wire, rope, or cable moving on a grooved wheel.

  • May be made up of one or many wheels.
  • Can be fixed in place or movable.
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6) Wheel and Axle:

Made up of two wheels of different diameters the turn together.

  • A longer motion on the wheel produces a shorter more powerful motion on axle.
  • Enable the user to apply a greater force on an object.
  • But the user must move the wheel a greater distance to apply the force.
  • Can also be used to increase speed (ex. Bicycle).

** A simple machine can increase or change the direction of the force that you apply.

     But, the cost is that the force the user applies must move farther than the load.


The Complex Machine – A Mechanical Team

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Why complex machines? 

  1. As larger communities developed, newer more complicated machines developed.
  2. New larger energy sources like coal, oil, and electricity combined with new technologies, caused an industrial revolution.
  3. This led to an increase in people’s standard of living.
  4. But has also led to people now being dependent on technology.

Complex Machines:

A system in which simple machines all work together.

System:

A group of parts that work together to perform a function.

  • (Ex) bicycle

Subsystem:

A smaller group of parts in a complex machine with one function.         

  • (Ex) braking and steering

 


Subsystems that Transfer Forces

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Linkage:

A belt or chain to transfer energy from a energy source to an object.

  • (Ex) bicycle chain
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Transmission:

A special type of linkage for transferring energy from the engine  to the wheel in large vehicles such as cars or trucks.

  • more useful when larger loads must be moved.
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Gears:

A pair of wheels with teeth that interlink; when they rotate together, one gearwheel transfers turning motion and force to the other.

  • are important because control the transfer of energy in a system.
  • gear wheels work together in gear trains (2 or more gears).

DRIVING GEAR:

Gear that has original force applied to it.        

DRIVEN GEAR:

Gear that receives the force after.                                                              


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How do gears affect speed?

(I) When driving gear is smaller  than the driven gear   =  The turning speed in the system increases.

  • For every turn the larger wheel makes the smaller gear will do many more.
  • Are called multiplying gears.

(II) When the driving gear is larger than the driven gear  =   The turning speed in the system decreases.

  • Are called reducing gears.
  • In some systems the gears are meshed together, but in some cases they are  connected by a linkage.

Understanding of mechanical advantage and work helps determine the efficiency of machines

 

Understanding simple & complex machines advanced world exploration,

  • (Ex) Sail boat

Machines Make Work Easier.

-       A winding road is actually a series of inclined planes with switchbacks, which allow cars to drive up a steep hill.

 SWITCHBACKS OF LOMBARD STREET SAN FRANCISCO

SWITCHBACKS OF LOMBARD STREET SAN FRANCISCO

Mechanical Advantage :

Amount by which a machine can multiply a force. Also called the force ratio

Input Force:

Force applied to the machine.

Output Force: 

Force the machine applies to the object.

Force is measured in Newtons (N).

 

                        Mechanical  Advantage  (MA) =   Force Output (N) / Force Input (N)                                                                       

EX 1

To pull a weed out of a garden, you can apply a force of 50 N to the shovel. The shovel applies a force of 600 N to the weed. What is the mechanical advantage of the shovel?

EX 2

To pry open a soda can lid, you can apply a force of 50 N to a car key. The car key applies a force of 390 N to the lid. What is the mechanical advantage of the car key?

EX 3

To pry a wooden board off of a treehouse, you can apply a force of 50 N to a lever. The lever applies a force of 750 N to the board. What is the mechanical advantage of the lever?

REVIEW QUESTIONS

 

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Speed Ratio

Speed:

Measures the distance an object travels in a given amount of time.

Speed =   Distance (m)/ Time (s) 

 

Speed Ratio:

Measure of how the speed of the object is affected by a machine.

SR describes how much faster the user is moving than the load is working.

Speed Ratio  (SR)   = Input Distance (m)/ Output Distance (m) 

Ex 1

A gear mechanism of two gear is in motion. The driving gear moves a total of 3m, while the driven gear moves a total of 12m. What is the speed ratio of this mechanism?    

EX 2

A pulley system is pulled a distance of 10 m, this moves a box that is attached to the pulley 1.5m. What is the speed ratio of the pulley system?

                        

** A machine can increase or change the direction of the force that you apply. But, the cost is that the force the user applies must move farther than the load.

REVIEW QUESTIONS


A Mechanical Advantage Less Than 1

Useful for tasks that do not require a large output force.

  •  (Ex) Bicycle – the output force is used for speed.

The Effect of Friction

  • Mechanical Advantage does NOT always equal Speed Ratio.
  • Friction can affect MA, but not SR.
  • Speed ratio represents the ideal mechanical advantage (No friction).
 FRICTION WELDING OF TWO METAL PIECES

FRICTION WELDING OF TWO METAL PIECES

Friction:

Force that opposes motion.

  • caused by the roughness of surfaces.
  • as roughness of a surface increases so does the effect of friction.
  • friction creates HEAT, and must be released to protect the system.

Efficiency

Efficiency:

Measurement of how well a machine or device uses energy.

  • affected by friction.
  • most energy lost is unusable (ex. Heat).                                                

 

Efficiency  =   Mechanical Advantage /  Speed Ratio                                                                     

 

Most complex machines are very inefficient: waste energy.

ex) Car – 15% efficient.


The Science of Work

Work:

Done when a force acts on an object to make the object move.

Movement is needed before one can say that work has been done.

Also reffered to as 'Energy'

Measure in Joules (J) (N x m) 

Amount of work done depends on 2 things:

  1.  amount of force exerted on the object
  2.  distance the object moved in the direction of the applied force.

Work (N x m) = Force (N) x Distance (m)

- The joule is also used in calculating Energy.

EX 1

You apply 300 N of force in 15 m. How much work did you do?

EX 2

A forklift lifts a box 2 m by applying 1000 N of force. How much work did the forklift do?

Ex 3

You have used 1000 J of energy to apply a force of 200 N to an object. How far did that object move?

REVIEW QUESTIONS

Power:

How much work is achieved in a certain amount of time, measured in Watts

Power (W) = Work (J) / Time (s) 

EX 1

You apply 200 J to an object in 15 s. How much power did you use?

EX 2

An engine provides 5000 J of work to an axle over the period of 10 seconds. How much power does the engine have?

Ex 3

A horse pulls a wagon by working 4500 J over a time of 6 s. How much power does the horse produce? 


Energy and Work

Energy and work are closely related, can not have one without the other.

(Ex) Car – needs energy (gasoline) in order to work (move)

Work and Machines

Using a machine does not decrease the amount of work, it decreases the force.

         Work Input   =   Work Output

This equation is affected by friction (just like mechanical advantage)

Here is another way of calculating efficiency: 

            Efficiency = Work Output/ Work Input  

 

EX 1

A construction worker puts 20 J of energy in to one strike of his hammer on the head of a nail. The energy transferred to driving the nail in to the wood is 8.0 J. What is the efficiency of the construction worker's hammering?

EX 2

Mr. K spent 25 J of energy to spike a volleyball over the net. A player received that volleyball and determined that the energy transferred to the ball was 20 J of energy. What is the efficiency of Mr. K's spike? 

EX 3

A particular chemical process has an energy efficiency of only 3.00%. To complete this large-scale chemical process, 140,000 J of energy is input. What is the energy output of this process?

REVIEW QUESTIONS