Lesson Plan: Introduction to Mechanical Systems
Class : Grade 8 Science Date :
Class Length : 47 minutes Teacher : Kyle McKenzie
Unit : Mechanical Systems
GLO’s & SLO’s from Alberta Program of Studies Knowledge and STS
- Illustrate and development of science and technology by describing, comparing and interpreting mechanical devices that have been improved over time
- Investigate and provide examples of mechanical devices used in the past to meet particular needs (e.g. devices used to move water or to be moved by water such as the Persian wheel, Archimedes Screw or the mill wheel)
- Analyze machines by describing the structures and functions of the overall system, the sub systems and component parts
- Analyze a mechanical device by:
- Describe the contribution of individual components or sub systems to the overall function of the device
- Identify components that operate as simple machines
- Identify the source of energy for some familiar mechanical devices
- Identify linkages and power transmissions in a mechanical device and describe their general function (e.g. identify the purpose and the general function of belt drives and gear systems within a mechanical device)
- 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
- 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 its impacts on humans and the environment
Lesson Objectives : The students will…
a) Know the methods of energy transfer are: Chain Drives
Belt Drives
Gears
Drive shafts
b) Recognize that most energy transfer between systems occurs with the use of the wheel and axle being connected to another wheel and axle by some means
c) Evaluate different scenarios and make a judgment as to which linkage would perform the best given the different parameters of the scenario
d) Recognize the difference between the driving gear and the driven gear and why it is important to classify each in order to establish if the system is a multiplying or reducing system
Materials :
The Teacher will need :
- Lap Top and Projector - Power Point presentation “Gears & More Gears”
- Text Book “Science in Action 8” - Demo Mountain Bike
- “Gears & Linkages” Worksheet - Demo Egg Beater
The Students will need :
- Science Binder
- Pen and paper for notes - Text books
Lesson Plan 10: Gears & More Gears Continued
Procedure :
Introduction :
- Go over the different methods of linkages and the pros and cons of each.
- The students should already know about CHAIN, BELT, GEAR, and SHAFT drive systems
- Quickly reiterate the pros and cons of the different methods of transferring energy, make sure that the cost of the different methods is front and center in any discussion that takes place
- The students should recognize the belts are cheaper than chains which are cheaper than drive shafts. The ability to handle heavy loads, slippage, and speed should also be discussed in the review
- Allow student generated discussion to lead this portion of the class and check for overall formative assessment of student understanding of the topic
- Depending on the student’s level of completion of the worksheet that was handed out to them in the previous class, go over the questions on the front side of the sheet.
Time = 6 minutes
Body :
- Have the power point presentation “Gears & More Gears” ready on the screen
- As the students progress through the discussion and power point presentation, have them copy out any power point slides that have green check marks in the top right corner. Also, be sure the students copy down as many diagrams about the linkages being discussed as possible.
- The power point will start by covering the difference between the driven and the driving gear in a gear system
- The students should also cover the importance of labeling such gears and how that will relate to defining multiplying and reducing gear systems
- Have the students copy down the diagrams of the bicycles and label the driving and the driven gear. Make sure that students refer to this diagram when they are questioned about which gear is which in any formative questions
- Form that point the power point will get into the difference between multiplying and reducing gear systems
- Have the students copy down the information on each and accompany each definition with a simple diagram on the following slide.
- In the margin, it is important to note for their assignment, that reducing gears have a low gear ratio and multiplying gears have a high gear ratio
- Make sure the students copy down all of the diagrams and label them appropriately
- Ask questions of the students to check for understanding such as:
“If we want to climb a hill on our bike, how would we want the gears to be set up to create the best reducing gear system to make climbing the hill easier”
“Multiplying gears means the out put speed is?.... Faster”
“Reducing gears means the out put speed is?... Slower”
“Once we reach flat land and we want to speed up on our bike, how should we set up the gears to achieve the fastest speed?”
- As the students copy down the notes, pass around the egg beater for the students to see how the very large driving gear causes the speed of the two very small driven gears to turn quickly
- Go over the difference between a Low and High gear ratio. Explain that the numbers in the ratio can be deceiving because even though the first number in the ratio might be very large (exchangeable for high) this means exactly the opposite and that ratio is actually very low
- The further the two numbers are from a one to one ratio, usually means the low the gear ratio is. And visa versa, the closer the two numbers are to one and other (1 : 1) the higher the gear ratio will be
- The first number in the ratio refers to the driving gear, and the second number in the ratio refers to the driven gear
Time = 30 minutes
Lesson Plan 10: Gears & More Gears Continued
Activity:
- Lastly, have some students volunteers come up to the front of the classroom and place the bike in low gear. Make sure the other students agree that the bike is in low gear when the front sprocket is on the smallest gear and rear sprocket is on the largest gear.
- At that point have a two impartial students come up to the front of the room and turn the peddle to make an approximate mental note of the force they used to turn the tire.
- Now have to other students come up to the front and place the bike in high gear. Have the rest of the class reach a consensus that the bike is in high gear when the front
sprocket in on the largest gear and the rear sprocket is on the smallest gear.
- Then, have the same two impartial students turn the peddles on the bike and decide in which case it was easier
- They should decide that on the first attempt, is was much easier to turn the wheels on the bike
- Have the students take out their work sheets from the previous day and use the last bit of class to work on them
- Make sure that the students know that the worksheet is due for tomorrow and will be marked in class
- Students must have this worksheet finished before class tomorrow, because we will be marking it first thing in class (no finishing it during class)
Time = Rest of Class
Pork Chop :
- If time permits, have the students make their way out the parking lot to look under the hood of the Jeep. Give them the chance to see how a “Serpentine Belt” power the accessories of a motor
Show the students that the energy produced by the motor of a vehicle does not just power the drive wheels of the vehicle, but it also power a bunch of smaller SUBSYSTEMS underneath the hood if that has not already been done as a pork chop activity.
OR
- Have the students begin researching the three different jeeps that we will be testing in the jeep creep competition on Friday. Show the students to the three different models of jeeps that will be used and give them a starting point for their research.
- The web sites to use are:
Time = Rest of Class
Assessment :
- There will be formative assessment of students understanding through students lead discussion of the topic regarding the different linkages that they have seen in the real world
- As well, the students will be engaged in some demonstrations using a mountain bike to figure out which situation would require different gear combinations, the students will have to use their problem solving skills and work as a class team to decide which gear combination would be the best for each scenario
- Finally, the students will have a worksheet in which they will have to carefully fill some blanks to make sense of a paragraph that talks about the multiplying and reducing gear systems. Students will have to carefully to read through the selection and use their problem solving skills to come up with a sequence of definitions that will appropriately describe multiplying and reducing gears.