Unit D: Mechanical Systems

STS and Knowledge

1. Illustrate the development of science and technology by describing, comparing and interpreting mechanical devices that have been improved over time
332-341 / Investigate and provide examples of mechanical devices used in the past to meet particular needs (e.g. describe and interpret devices developed to move water or be moved by water, such as the Persian Wheel, Archimedes’ screw, mill wheel)
Illustrate how a common need has been met in different ways over time (e.g. development of different kinds of lifting devices)
Illustrate how trial and error and scientific knowledge both play a role in technological development (e.g. development of aircraft)
Steam Engine: Fuel such as coal or wood is burned to heat water in a boiler outside the engine. The water changes to steam and drives the engine.
-Know figure 4.56 page 334
-Steam engines were not the first mechanical devices to run on steam. In 150 B.C. Hero of Alexandria of Egypt wrote a book describing many other mechanical devices.
-Steamboats were an important means of transportation in Canada.
-Know diagram 4.60 page 336, Turning Wheels
Piston: A moveable disk or platform that fits inside a closed cylinder. When the piston moves it causes an attached rod to move. The rod in turn is attached to another part of the machine such as a crankshaft in the engine.
Exhaust valve: On the left side of the machine, it opens and allows old cooled steam to escape.
Internal combustion engine: The term “internal combustion” describes the way the engine works. The burning of fuel occurs inside the engine. No external furnace, boiler or water is needed. The fuel is burned inside the cylinders.
-Know figure 4.61 on page 338
Crankshaft: Most car engines have pistons that move up or down or back and forth. The crankshaft si a part that changes the motion to rotary motion which turns the automobile’s wheels. The power to move the pistons comes from the energy released by burning gasoline.
2. Analyze machines by describing the structures and functions of the overall system, the subsystems and the component parts
Analyze a mechanical device by:
-describing the overall function of the device
-describing the contribution of individual components or subsystems to the overall function of the device
-identifying components that operate as simple machines
270-275 / Lever: A simple machine that changes the amount of force you need to put on an object to move that object.
Fulcrum: The fixed point on a lever, the rotational point.
Effort Force: The force exerted on a lever to make it move.
Load: The mass of an object lifted by the lever.
Effort Arm: The distance between the fulcrum and effort force.
Load Arm: The distance between the fulcrum and the load.
There are three classes of Levers
Class 1: fulcrum is at the center Ex. Teeter totter.

Class 2: Load is at the center Ex. Wheel barrel

Class 3: Effort force is at the center Ex. Hockey stick

Identify linkages and power transmission in a mechanical device, and describe their general function (e.g., identify the purpose and general function of belt drives and gear systems within a mechanical device)
285-289 / Winch: Small cylinder that has a crank or handle. This is an example of a wheel axle device.( Page 285 fig 4.12)
Radius: Distance from the center of the wheel to the circumference.
Wheel and axle device: The “wheels” do not have to be round. As long as there are two turning objects attached to each of their centers, and one causes the other to turn, it is a wheel axle device.
Gear: A rotating wheel like object with teeth around the rim. Think of the gears on a bike.
Gear Train: A group of two or more gears. The teeth of one gear fit into the teeth of another gear. When one turns so does the other.
Driving Gear (also called the driver) : First gear, the one in which the initial force is applied.
Driven Gear (also called the follower) : Second gear, the one that gets driven
See figure 4.15 on page 287.
Sprocket: A gear with teeth that fit into a chain, like on your bike.
Identify the source of energy for some familiar mechanical devices
296-298 / Kinetic Energy: Energy of motion. When you push on the pedals of your bike.
Most of today’s machines are not powered by people. The two main natural resources for energy of machines are fuel, like gasoline, and electrical energy.
Potential Energy: Stored Energy. Most of the energy for machines, even your body, is stored as chemical energy.

Know figure 4.26 on page 297

Transmission: Energy can be transmitted as well as converted. In transmission, energy can be transferred from one place to another, and no energy is changed or converted.
3. Investigate and describe the transmission of force and energy between parts of a mechanical system
Analyze mechanical devices to determine speed ratios and force ratios .
Build or modify a model mechanical system to provide for different turning ratios between a driving and driven shaft, or to achieve a given force ratio
289 /

SPEED RATIO

The relationship between the speed of rotations of a smaller gear and a larger gear.
Speed Ratio=
Number of driver gear teeth
Number of follower gear teeth
Compare theoretical and actual values of force ratios, and propose explanations for discrepancies (e.g., identify frictional forces, and estimate their effect on efficiency)
298-299 / Efficiency: Tells you how much of the energy that you gave to the machine was transferred to the load by the machine. It is a comparison of the useful work provided by the machine or a system with the work supplied to the machine or system.
Efficiency= Work done by lever or loadX 100%
Work done on lever by effort force
The higher the efficiency, the better the lever is at transferring energy.
Identify work input and work output in joules for a simple machine or mechanical system (e.g., use a device to lift a measured mass an identified distance, then calculate the work output)
276-281 /

WORK: The product of the force exerted times the distance moved and is measured in Joules.

W = F x D
Work = Force X Distance
Example: The force exerted on a lever is 2N. It moves a distance of 0.6 M Calculate the work.

Work = 2N X 0.6m

Work = 1.2 J
Incline Plane: a ramp or slope that reduces the force needed to lift something.
Input Work: The work you do on a machine
Output Work: The work the machine does on the load

Mechanical Advantage

The comparison of the force produced by a machine to the force applied to the machine
Mechanical Advantage (MA) = Load Force (LF)
Effort Force (EF)
A force of 500N is applied to a branch. The back of the truck weighs 2500N. What is the MA?
MA = 2500NMA= 5
500 N
*Page 281 Second way to calculate MA.
Describe fluid pressure qualitatively and quantitatively, by:
-explaining how forces are transferred in all directions
-describing pressure in unit of force per unit area
304-308 / Pressure: The force acting over an area.
Pressure = Force

Area

Pascal’s Law

The pressure exerted on a contained fluid is transmitted undiminished in all directions throughout the fluid and perpendicular to the walls of the container.
Hydraulic Lift: A mechanical system that raises heavy objects. Example: A vehicle on a service station lift.
Closed System: Self-contained collection of parts, nothing exits or enters.
Describe how hydraulic pressure can be used to create a mechanical advantage in a simple hydraulic jack (e.g. describe the relationship among force, piston size and distance moved, using different sized syringes linked by tubing)
308-310 / Mechanical Advantage: Load divided by the effort force.
MA= Load force
Effort Force
Suppose you wanted to lift a 90N load a distance of 2M using a hydraulic lift, how far would you have to push the piston to exert the effort force? There is a 10 N effort force.
W= F X d
W (effort) = 10N X d (effort)
W (load) =90 N X 2M
W (effort)= W (load)
Therefore 10N X d = 180 J
D (effort)=180J
10 N
= 18 M
313-325 / Describe and interpret technologies based on hydraulics and pneumatics (e.g., applications in hydraulic lifts and air-driven tools)
Hydraulic Systems: Uses the force of liquid in a confined space. They apply two essential characteristics of liquids; their incompressibility and ability to transmit pressure.
Pneumatic Systems: Air passes through a pneumatic device under high pressure and escapes outside the device. The high pressure air may come from a machine that draws in outside air and compresses it. Hoses then carry the high pressure air to the pneumatic device. Does not seal the air or gas in a mechanical system.
Examples of pneumatic machines are :
  • jackhammer know diagram on page 316 (4.37)
  • staple gun
  • sandblasters
  • pressurized casts (high pressure that enables the cast to fit properly and snugly
  • hovercraft
*Review fig 4.43 on page 318
Riding on Air: Hovercraft: Powerful pumps draw in outside air and pump it out through holes in the bottom of the hovercraft. A “skirt” around the bottom holds enough air to support the hovercraft. Propellers drive it forward and rudders steer it.
Hydraulics at Work: Heavy equipment machinery contain tanks filled with hydraulic fluid and pumps for pressure. Valves direct this pressure and fluid through the machinery where there is force needed.
Hydraulics in Flight: In a plane, the pilot uses hydraulics to lower the flaps and slats to slow he aircraft during landing. Hydraulics are then used to raise spoilers when the aircraft touches down. Fig 4.45 on page 321.
Hydraulics and Pneumatics in the Body
Your body is a pneumatic system as well as hydraulic system. Lungs expand and contract to allow you to breathe which depends on changes in air pressure. Your hearts moves blood through vessels throughout the body.
Valve: A valve is used to control fluid. A valve is a moveable part that controls the flow of fluid by opening or closing.
Pumps: Many pumps use automatic valves controlled by pressure to move fluids in a specific direction. The valve is pushed open by pressure on one side and will close if the pressure becomes greater on the other side of the valve.
4. Analyze the social and environmental contexts of science and technology, as they apply to the development of mechanical devices
Evaluate the design and function of a mechanical device in relation to its efficiency and effectiveness, and identify its impacts on humans and the environment
283 / Ergonomics: The science of designing machines to suit people.
Comes from the Greek words Ergon meaning “work” and “nomos” meaning “natural laws.”
Develop and apply a set of criteria for evaluating a given mechanical device, and defend those criteria in terms of relevance to social and environmental needs
Hydrogen Fuel Cell: A bus can be powered by this. It fuels a chemical reaction that uses hydrogen and oxygen from the atmosphere to make electricity. Example: Figure 4.69, Page 345
342-350 / Illustrate how technological development is influenced by advances in science, and by changes in society and the environment
Science has greatly improved the machines that we use today by increasing the size and use of vehicles as well as making fuel more efficient
-Emissions are a problem technology as brought about with the advancement of machinery
Mass Production: making large amounts of a standardized item by standardized mechanical processes. Example: Canning of Foods, Manufacturing home appliances in a factory etc.

Page 1 of 9