Unit D Lesson D5
Completion requirements
Lesson D5: Machine Efficiency
Video Lesson
Why do machines not use all of their input energy to do useful work? Watch this video to learn more about machine efficiency.
Lesson D5: Machine Efficiency
Figure D.2.5.1 – Lubricants help increase machine efficiency.
Figure D.2.5.2 – Motor oil lubricates moving parts in car engines.
Figure D.2.5.3 – Many machines require specific substances to protect their parts and provide lubrication.
Reading and Materials
for This Lesson
Science in Action 8
Reading: Pages 290–292
Materials:
No additional materials needed for this lesson.
The Squeaky Wheel Gets the Grease
A squeaky bicycle wheel or door hinge is a very unpleasant sound. Squeaking sounds in machines occur when parts rub against each other, creating friction. The force of friction produces wasted heat and sound energy.
Putting lubricant on machine parts greatly increases a machine’s efficiency. A lubricant is usually an oily or greasy substance. A thin coat of lubricant on metal machine parts helps them move smoothly and quietly, instead of grinding against each other.
Many machines need to be lubricated regularly. You should always use a lubricant that is specifically designed for a particular machine. Car engines need motor oil, on fast-moving engine parts. Sewing machines occasionally need a few drops of oil to make them feed thread correctly. Bicycle chains require oil to reduce friction between the chain and the gears.
A squeaky bicycle wheel or door hinge is a very unpleasant sound. Squeaking sounds in machines occur when parts rub against each other, creating friction. The force of friction produces wasted heat and sound energy.
Putting lubricant on machine parts greatly increases a machine’s efficiency. A lubricant is usually an oily or greasy substance. A thin coat of lubricant on metal machine parts helps them move smoothly and quietly, instead of grinding against each other.
Many machines need to be lubricated regularly. You should always use a lubricant that is specifically designed for a particular machine. Car engines need motor oil, on fast-moving engine parts. Sewing machines occasionally need a few drops of oil to make them feed thread correctly. Bicycle chains require oil to reduce friction between the chain and the gears.
Watch More
Lubricating a Bicycle Chain
This video explains how to lubricate a bicycle chain.
This video explains how to lubricate a bicycle chain.
Think • Interpret • Decide
Download:
DOWNLOAD this document. It has a table for you to record the results
of your calculations. It also provides space for you to do your math work, so it would be a good idea to print this document.
Instructions:
A student did an experiment to compare the efficiency of three simple machines. He measured the input work of each machine in lifting a 1 kilogram block.
First, the student measured the force required to lift the block straight upwards. He lifted the block with a spring scale. It took an applied force of 10.0 newtons lifting the block 2.00 metres straight up. The student used these measurements to calculate the amount of output work needed to lift the block. Remember that the output work is the actual energy required to do a task, not counting any extra energy wasted on friction.
Next, the student tried lifting the block to a height of 2.00 metres using different simple machines. He measured the input force and distance used to lift the block with the simple machine. His experimental results are shown in the table below.
First, the student measured the force required to lift the block straight upwards. He lifted the block with a spring scale. It took an applied force of 10.0 newtons lifting the block 2.00 metres straight up. The student used these measurements to calculate the amount of output work needed to lift the block. Remember that the output work is the actual energy required to do a task, not counting any extra energy wasted on friction.
Next, the student tried lifting the block to a height of 2.00 metres using different simple machines. He measured the input force and distance used to lift the block with the simple machine. His experimental results are shown in the table below.
Lifting a Block With Simple Machines
Questions
After you have examined the table carefully and carried out calculations to determine the student’s input work and efficiency, 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 table carefully and carried out calculations to determine the student’s input work and efficiency, carefully consider the following questions. Then, type or write your answers. When you have your answers, click the questions for feedback.
Output work is the amount of work necessary to lift the block straight up to a height of 2.00 metres. Output work is calculated by multiplying the output force and output distance. In this experiment, 10.0 N multiplied by 2.00 m equals 20.0
J of output work.
Input work for each simple machine is calculated by multiplying input force and distance. Efficiency equals the output work divided by the input work times 100%. The calculated results for input work and efficiency are shown in the table below.
Input work for each simple machine is calculated by multiplying input force and distance. Efficiency equals the output work divided by the input work times 100%. The calculated results for input work and efficiency are shown in the table below.
If all machines are completing the exact same task, the machines with a greater input work will have a lower efficiency. A low efficiency machine wastes more input force producing undesirable forms of energy such as heat (from friction). Some
machines are more efficient than others because they produce less friction and a larger amount of useful output work.
Machines that produce more useful output work create less friction. Machines that produce less friction have less rubbing between surfaces. In this experiment, the lever was most efficient because it wasted the least amount of energy using force
to overcome friction. The lever did not involve two surfaces rubbing against each other for a long distance. The pulley had a medium efficiency because it produced some friction as the rope rubbed against the pulley. The inclined plane produced
the most friction as the bottom of the block rubbed against the ramp surface for 5 metres.
Figure D.2.5.4 – Sports cars have good aerodynamics.
Figure D.2.5.5 – Thin aerodynamic bicycles reduce drag.
Figure D.2.5.6 – Velomobiles are aerodynamic, pedal-powered tiny cars.
What a Drag!
Vehicles experience a force called drag or air resistance. Drag is caused by air particles rubbing against a vehicle. Drag is a form of friction which slows down vehicles and reduces their efficiency.
Vehicle shape affects drag. Large boxy vehicles with parts that stick out usually experience more drag, because they have a larger surface in contact with the air.
Aerodynamic vehicles have shapes that reduce drag and increase efficiency. Round thin vehicles experience less drag because they experience less contact with air particles. When a vehicle experiences less air resistance, the input work of the vehicle is lower because it has to put less work into overcoming friction, and as a result, its efficiency increases.
For example, bicycle racers want all of their pedalling effort to make the bicycle move faster. Bicycle racers ride thin lightweight bikes that experience less drag, which makes pedalling more efficient.
Vehicles experience a force called drag or air resistance. Drag is caused by air particles rubbing against a vehicle. Drag is a form of friction which slows down vehicles and reduces their efficiency.
Vehicle shape affects drag. Large boxy vehicles with parts that stick out usually experience more drag, because they have a larger surface in contact with the air.
Aerodynamic vehicles have shapes that reduce drag and increase efficiency. Round thin vehicles experience less drag because they experience less contact with air particles. When a vehicle experiences less air resistance, the input work of the vehicle is lower because it has to put less work into overcoming friction, and as a result, its efficiency increases.
For example, bicycle racers want all of their pedalling effort to make the bicycle move faster. Bicycle racers ride thin lightweight bikes that experience less drag, which makes pedalling more efficient.
Watch More
Aerodynamics
Watch this video to see how car aerodynamics are tested in a wind tunnel.
Watch this video to see how car aerodynamics are tested in a wind tunnel.
This video shows that cyclists can also be tested for aerodynamics in a wind tunnel.
Velomobiles are pedal-powered miniature cars. Watch this video to see an aerodynamic velomobile in action.
Connections
Figure D.2.5.7 – Fuel efficient cars provide more output work for input energy.
>> Fuel Economy
Some people care about fuel economy when they purchase a vehicle. Fuel economy is a way of expressing a car’s efficiency. Fuel economy refers to how much gasoline a vehicle uses to drive a particular distance. In Canada, fuel economy is measured in litres per 100 kilometres. Cars with a high fuel economy require less input fuel energy for the output work of driving. Cars with a high fuel economy are usually small and aerodynamic.
There are several advantages to driving fuel-efficient cars. Efficient cars cost less to drive, because they don’t need as much gasoline. Burning less gasoline emits less carbon dioxide into the atmosphere, which reduces the effects of climate change.
Watch More
Fuel Efficiency
These news reports show tiny aerodynamic fuel-efficient cars designed by university students.
These news reports show tiny aerodynamic fuel-efficient cars designed by university students.
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 5 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.
Machines produce less output work than energy put into them, due to friction. Friction changes some of the input work to non-useful heat and sound. A machine’s input and output work would be the same amount only in an ideal situation without
any friction.
Inefficient machines usually produce lots of friction. Friction between rubbing parts can make a machine noisy. Friction also produces heat, so the machine might feel hot. Friction is increased by rough surfaces moving against each other, so
the machine might appear rusty.
A machine with many gears has more places where gears touch and rub against each other. This creates more friction, which makes the machine less efficient.
The output work of the machine required to lift the child is 45 J. The input work by the adult into the machine is 60 J. Efficiency is calculated by taking the output work divided by the input work times 100%. This results in 45 J /60 J
x 100% = 75% efficiency.
The girl’s input work is equal to her force of 200 N multiplied by a distance of 5.00 m, which equals 1000 J of input work. If 200 J of work are lost to heat and sound, the output work of the ramp is 1000 J minus 200 J, which equals 800 J of
output work. This results in 800 J /1000 J x 100% = 80% efficiency.