Unit D Lesson D9
Completion requirements
Lesson D9: Evaluating a Mechanical Device
Video Lesson
How do people decide if a machine is worth buying? Watch this video to learn more about evaluating mechanical devices.
Lesson D9: Evaluating a Mechanical Device
Figure D.3.9.1 – A scythe is a sharp curved blade used to cut grass.
Figure D.3.9.2 – Push lawn mowers have turning blades.
Figure D.3.9.3 – Riding lawn mowers are gasoline-powered.
Reading and Materials
for This Lesson
Science in Action 8
Reading: Pages 305–315
Materials:
Balloon, straw, rubber band, tape, 4 round objects for wheels (such as bottle caps or old CDs), 2 long objects for axles (such as straws or skewers), scissors, object for car body (such as a cup, empty bottle, or small box), stopwatch, tape measure,
masking tape, glue.
Lawn Mowers
Before lawn mowers, people cut grass by hand with scythe blades, which took a lot of effort. Lawn mowers were invented in the mid-1800's. The first lawn mowers were push mowers with rotating blades. Since then, people have improved the design of lawn mowers. In the early 1900’s, the first gasoline-powered riding mower was invented. This invention greatly reduced the amount of work people had to put into mowing a lawn. Gasoline motors were also added to push mowers, to spin the blades quickly.
However, burning gasoline creates carbon dioxide gas in the atmosphere, which contributes to climate change. To reduce the negative effects of lawn mowers on the environment, some companies are improving the design of the original non-gasoline push mower, making it easier to use. Inventors are also developing robotic lawn mowers, that run with electric batteries. A robotic lawn mower charged by renewable sources of electricity, such as solar energy, is also better for the environment.
Before lawn mowers, people cut grass by hand with scythe blades, which took a lot of effort. Lawn mowers were invented in the mid-1800's. The first lawn mowers were push mowers with rotating blades. Since then, people have improved the design of lawn mowers. In the early 1900’s, the first gasoline-powered riding mower was invented. This invention greatly reduced the amount of work people had to put into mowing a lawn. Gasoline motors were also added to push mowers, to spin the blades quickly.
However, burning gasoline creates carbon dioxide gas in the atmosphere, which contributes to climate change. To reduce the negative effects of lawn mowers on the environment, some companies are improving the design of the original non-gasoline push mower, making it easier to use. Inventors are also developing robotic lawn mowers, that run with electric batteries. A robotic lawn mower charged by renewable sources of electricity, such as solar energy, is also better for the environment.
Figure D.3.9.4 – Some home lawn mowers have gasoline motors.
Figure D.3.9.5 – Robotic lawn mowers are a new invention.
Watch More
The Many Ways to Cut Your Grass
Watch this video to learn about the inventor of the lawn mower.
Watch this video to learn about the inventor of the lawn mower.
This video explains the benefits and drawbacks of using a push reel lawn mower.
Watch this video to see a lawn mower bicycle invention. How is this invention good for the environment?
This video explains how robotic lawn mowers work.
Should you buy a robotic lawn mower? Watch this video for an evaluation of robotic lawn mowers.
Figure D.3.9.6 – Machine testing organizations rate machines.
Figure D.3.9.7 – The CSA logo is found on many products.
Figure D.3.9.8 – Several safety and consumer protection agencies have logos that appear on the products we buy.
Machine Testing Organizations
When you want to buy a new machine, how can you learn more about it? How do you know if the machine works effectively? How do you know the machine is safe to use? Some people have formed organizations that test and evaluate machines, to provide information for consumers.
The CSA Group is a product-testing organization. The CSA Group tests many machines and machine parts, especially electrical machines, to make sure they are safe to use. Machines that have been have evaluated and confirmed safe are marked with a CSA symbol (Figure D.3.9.7). Check the appliances in your house for the symbol – are they CSA approved?
Another product-testing organization is Consumer Reports. This organization evaluates different products that people buy, including machines like appliances and cars. They publish a magazine and website with their results. If you want to buy a new machine, information from Consumer Reports helps you compare different brands of machines for their effectiveness, safety, and reliability.
When you want to buy a new machine, how can you learn more about it? How do you know if the machine works effectively? How do you know the machine is safe to use? Some people have formed organizations that test and evaluate machines, to provide information for consumers.
The CSA Group is a product-testing organization. The CSA Group tests many machines and machine parts, especially electrical machines, to make sure they are safe to use. Machines that have been have evaluated and confirmed safe are marked with a CSA symbol (Figure D.3.9.7). Check the appliances in your house for the symbol – are they CSA approved?
Another product-testing organization is Consumer Reports. This organization evaluates different products that people buy, including machines like appliances and cars. They publish a magazine and website with their results. If you want to buy a new machine, information from Consumer Reports helps you compare different brands of machines for their effectiveness, safety, and reliability.
Think • Interpret • Decide
Buying a Vehicle
Most adults own a personal vehicle, which is a very expensive purchase. Before buying a vehicle, many people research and collect information about different vehicles, to compare different options.
For example, two different families want to buy a new vehicle. Both families have two parents and two school-aged children.
The first family lives in a large city. One parent takes a bus to work and the other parent has a half-hour drive to and from work, five days a week. The two children take a bus to school. Sometimes the family needs to drive to the kids’ soccer games on the weekend.
The second family lives on a farm, which is a ten minute drive on dirt roads from the nearest town. The two children take a bus to school. The two parents work on the farm and go into town about three times a week, sometimes to buy supplies and equipment for the farm.
Based on the information in the following table, which vehicle would best meet the needs of each family?
Most adults own a personal vehicle, which is a very expensive purchase. Before buying a vehicle, many people research and collect information about different vehicles, to compare different options.
For example, two different families want to buy a new vehicle. Both families have two parents and two school-aged children.
The first family lives in a large city. One parent takes a bus to work and the other parent has a half-hour drive to and from work, five days a week. The two children take a bus to school. Sometimes the family needs to drive to the kids’ soccer games on the weekend.
The second family lives on a farm, which is a ten minute drive on dirt roads from the nearest town. The two children take a bus to school. The two parents work on the farm and go into town about three times a week, sometimes to buy supplies and equipment for the farm.
Based on the information in the following table, which vehicle would best meet the needs of each family?
| Vehicle | Time (in seconds)
to accelerate from 0 to 100 km/h |
Gas Mileage
(L per 100 km) |
Maximum
Cargo Load (kg) |
Passengers |
|---|---|---|---|---|
| Small compact car
|
8.1 | 7 | 385 | 5 |
| Pickup truck
|
6.3
|
12
|
1500 | 4 |
| Minivan
|
7.6
|
11
|
625 | 7 |
| Sports car
|
3.1
|
15
|
204
|
2
|
Questions:
After you have examined the information in the table carefully, consider the following questions. Then, type or write your answers. When you have your answers, click the questions for feedback.
After you have examined the information in the table carefully, consider the following questions. Then, type or write your answers. When you have your answers, click the questions for feedback.
The table compares the characteristics of different vehicles.
- The time to accelerate from 0 to 100 km/h describes how fast the vehicle can speed up. A lower acceleration number means that the car has a more powerful engine and speeds up faster.
- Gas mileage describes how much gasoline the car uses. A lower gas mileage number means that the vehicle uses less gas, so it costs less to fill up the vehicle.
- Maximum cargo load is the amount of weight that the vehicle can carry, including passengers. A lower cargo load number means that the vehicle can carry less weight.
The family in the city would want a vehicle that holds at least four passengers. This family uses a vehicle most days. One parent drives to and from work, which is at least one hour of driving each weekday. Since they drive a lot, they probably
want a vehicle that uses less gas, so it is less expensive to drive. This family doesn’t need to haul a lot of cargo in their vehicle.
The family on the farm would also want a vehicle that holds at least four passengers. This family does not use a vehicle everyday, but they need a vehicle that won’t get stuck on muddy roads. Since they buy farm supplies, they probably also need a vehicle that can carry heavy loads. Since this family doesn’t drive far everyday, gas mileage probably matters less to them than the vehicle’s ability to carry cargo.
The family on the farm would also want a vehicle that holds at least four passengers. This family does not use a vehicle everyday, but they need a vehicle that won’t get stuck on muddy roads. Since they buy farm supplies, they probably also need a vehicle that can carry heavy loads. Since this family doesn’t drive far everyday, gas mileage probably matters less to them than the vehicle’s ability to carry cargo.
The family in the city should buy the small compact car. This vehicle can hold up to five passengers, and it has the lowest gas mileage. This family does not need a high-power engine, and they don’t need to carry lots of cargo. Based on the
good gas mileage, it would be better for this family to buy the compact car than the minivan or truck. The sports car has poor gas mileage and it doesn’t have enough seats for the whole family.
The family on the farm should buy the pickup truck. This vehicle can hold up to four passengers. It has a somewhat fast acceleration, which means the engine has enough power to get unstuck from muddy roads. The pickup truck has about the same gas mileage as the minivan, but gas mileage doesn’t matter as much to this family. The deciding factor for the truck is that it can hold much more cargo weight than the minivan, which is good for hauling things around the farm. The small compact car or the sports car wouldn’t be good for this family, because neither of these vehicles has a lot of cargo load.
The family on the farm should buy the pickup truck. This vehicle can hold up to four passengers. It has a somewhat fast acceleration, which means the engine has enough power to get unstuck from muddy roads. The pickup truck has about the same gas mileage as the minivan, but gas mileage doesn’t matter as much to this family. The deciding factor for the truck is that it can hold much more cargo weight than the minivan, which is good for hauling things around the farm. The small compact car or the sports car wouldn’t be good for this family, because neither of these vehicles has a lot of cargo load.
Connections
Figure A.2.3.9 – Driverless vehicles drive with sensors and computers.
Figure A.2.3.10 – Most vehicle manufacturers are developing automatic features for their newest vehicles. Photo courtesy the NRMA
.
Figure A.2.3.11 – A true self-driving car won't even have a steering wheel.
>> Evaluating Driverless Vehicles
Driverless vehicles will likely become very common in the future. Driverless vehicles don’t need a human driver to press the gas pedal, steer, or brake. Instead, driverless vehicles have sensors which gather information about the vehicle’s surroundings. The sensors send this information to a computer, which makes quick decisions about how to drive the vehicle. Companies like Google and Tesla are designing and testing self-driving cars. As of 2015, some driverless vehicles have been sold to consumers.
To keep people safe, manufacturers and governments need to thoroughly test and evaluate driverless vehicles. Is there any situation that a driverless vehicle can’t anticipate? Can manufacturers program every possible road situation into the vehicle’s computer? Do driverless cars waste less gas compared to regular cars?
Watch More
Evaluating Driverless Vehicles
Driverless vehicles will change the way people live. What is the impact of driverless vehicles on the environment and people’s lives? Watch this video to learn more.
Driverless vehicles will change the way people live. What is the impact of driverless vehicles on the environment and people’s lives? Watch this video to learn more.
How do driverless vehicles react during unexpected situations? Watch this video to learn more.
Try It!
Photo courtesy of the San Jose Library.
Make a Balloon Car
Try this activity to make a balloon-powered car. After you build your car, you will evaluate your design to determine if you can improve it.
Materials:
Try this activity to make a balloon-powered car. After you build your car, you will evaluate your design to determine if you can improve it.
Materials:
- Balloon
- Straw
- Rubber band
- Tape
- 4 round objects for wheels (such as bottle caps or old CDs)
- 2 long objects for axles (such as straws or skewers)
- Scissors
- Object for car body (such as a cup, empty bottle, or small box)
- Stopwatch
- Tape measure
- Masking tape
- Glue
Safety Warning
Take care with scissors; don't cut yourself or anyone else!
Instructions:
- Watch the video at the end of the instructions to learn how to design a balloon-powered car. The video also shows the process of evaluating the car and making improvements to its design.
- Using your materials, design and build a balloon car. The car must:
- Have 4 wheels
- Travel in a straight line
- Travel 1 meter in 2 seconds or less
- Mark a starting line with masking tape on a smooth floor. Measure 1 meter from the starting line. Mark this position with another piece of masking tape as the finish line.
- Blow up the car’s balloon and pinch the balloon opening. Place the front wheels of the car on the starting line.
- Start the stopwatch. At the same time, release the car’s balloon.
- When the front wheels of the car cross the finish line, stop the stopwatch. Observe the time.
- Evaluate your balloon car.
- Did it travel in a straight line?
- Did it travel 1 m in 2 seconds or less?
- If your car did not meet the conditions in step 7, make adjustments to your car. Repeat steps 4–7 until your car meets the requirements.
- Watch this video to see this experiment and its results:
Question:
Think about the following question very carefully. Then, type or write your answer. After you have your answer, click the question for feedback.
Think about the following question very carefully. Then, type or write your answer. After you have your answer, click the question for feedback.
Evaluating the balloon car allowed you to see if it met the requirements. If your balloon car did not meet the specifications, you could troubleshoot and adjust the car’s design.
Sharing:
Congratulations on building a balloon-powered car! Consider sharing your car in the course Sharing Forum. Other students and your teacher would very much like to see it, so consider taking a photo or video of your car and posting it.
Congratulations on building a balloon-powered car! Consider sharing your car in the course Sharing Forum. Other students and your teacher would very much like to see it, so consider taking a photo or video of your car and posting it.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.
Unit D Lesson 9 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
-
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Be a Self-Check
Superhero!
Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
Manufacturers need to test and evaluate machines to make sure they perform their function properly. It also is important to make sure that machines are safe to use. For example, if an electrical device doesn’t work properly, it can start a fire.
If a car doesn’t work properly, it can cause a collision.
The car designer could test how much fuel the car uses to drive a certain distance. For example, the car designer could drive the car 100 km and measure how much fuel the car used over that distance. The less fuel that the car uses, the more
fuel-efficient it is.
Safety is the most important factor in evaluating an airplane. If an airplane is unsafe and crashes frequently, people will not want to fly in it. Many new airplanes are designed to be fuel efficient so they cost less to fly, but safety is still
more important than fuel efficiency.
Manufacturers want to sell their machines. A manufacturer might be more concerned about taking shortcuts to make money, rather than ensuring that their machines are safe and effective. Outside organization usually provide more truthful information
to consumers.
The bicycle designer could test the bicycle’s speed. For example, he could measure how many seconds it takes for the bicycle to travel 100 m.