Lesson D3: Complex Machines

Key Ideas     Unit Checklist

  Video Lesson

Watch this video to learn how people combine simple machines in subsystems to create complex machines with a specific purpose.

 
 

  Lesson D3: Complex Machines


Figure D.1.3.1 – Hand saws have many small wedges in a row.

Figure D.1.3.2 – A table saw spins fast to cut lumber.


Figure D.1.3.3 – Chainsaws spin at high speeds.
Reading and Materials for This Lesson

Science in Action 8
Reading: Pages 269–276

Materials:
Multi-geared bicycle, chalk or white pen.

Saws

People have used saws for thousands of years to cut wood and stone. Hand saws are simple machines with many small wedges in a row, creating a jagged edge. Circular saws were invented in the late 1700s. In a circular saw, small wedges are located around a wheel edge. The turning wheel and axle in a circular saw applies more force than a hand saw, especially if the wheel is connected to electricity.

A chainsaw contains gears that make a chain of sharp wedges turn around a bar. Hand-cranked chainsaws were invented in the early 1800’s. Doctors used these small chainsaws to apply more force while cutting bone during amputation surgery. Large modern chainsaws are used to cut trees, concrete, and ice. They are powered with gasoline or electricity, which turns the chain at high speeds.

Forestry workers operate large machines called harvesters to cut down trees. Harvesters contain a lever arm attached to a chainsaw. These complex machines do the task of logging with much less human effort.

Figure D.1.3.4 – The first hand-cranked chainsaws were used for surgery.
Figure D.1.3.5 – Forestry workers use log harvester machines to cut down trees quickly.

 Watch More

Saws

Watch this video to see how chainsaws work and how they are made.

 
 
 
 
Remember water wheels from last lesson? Early sawmills often used water wheels to cut wood for building.

 

 

Try It!

Changing Gear Sizes and Speeds

 What is the relationship between rotation speed and direction of rotation when combining gears together? 

Download:
 
DOWNLOAD this document. It provides a gear observations table you will use later in this activity. It also has a place for you to answer questions at the end of the activity.

Instructions:

  1. Click here to open the gear simulation in a new browser tab.

  2. In this activity we will assume Gear 1 is providing the force to make the gears turn. That makes Gear 1 the driving gear. Gear 2 is the driven gear.

  1. Set the Gear 1 Speed to “Medium”.

  2. Make sure the Gear 2 size is set to “Small”. You will notice the two gears are the same size and have the same number of teeth. Record the number of teeth in the Test 1 row of the Gear Observations table.

  3. RPM stands for “revolutions per minute”. Record the RPM for each gear in the Test 1 row of the Gear Observations table.

  4. Increase the Gear 2 size to “Medium”. Record the number of teeth and RPM for each gear in the Test 2 of the Gear Observations table.

  5. Increase the Gear 2 size to “Large”. Record the number of teeth and RPM for each gear in the Test 3 of the Gear Observations table.

  6. Click the box next to “Show Chain Drive”. Record the number of teeth and RPM for each gear in the Test 4 of the Gear Observations table.

Analysis Questions:

Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.

When both gears had the same number of teeth, both gears had the same RPM. The gears were turning at the same speed.
When the driving gear (Gear 1) was smaller than the driven gear (Gear 2), the driving gear had a higher RPM than the driven gear. The driven gear turned slower than the driving gear.
When the driving gear (Gear 1) was larger than the driven gear (Gear 2), the driving gear had a lower RPM than the driven gear. The driven gear turned faster than the driving gear.
Gears that are meshed turn in opposite directions. Gears that are connected by a chain turn in the same direction.
Making Gear 1 turn slower also makes Gear 2 turn slower. Making Gear 1 turn faster also makes Gear 2 turn faster. However, this does not affect the relationship between the two gears when the gear sizes are changed. If you look closely at details in the corner of the gear simulation, you will see “Gear Ratio”. When the ratio is 1:1, the speed of the gears are the same. When the Gear 2 size is increased, the Gear Ratio changes to 1:2, meaning that Gear 2 spins at one-half the speed of Gear 1 – this ratio holds no matter what the speed of the driving gear is.

  Try It! 

Making Gear Trains

Gears can help change the speed and direction of motion. Try the GearSketch simulation to experiment with how gears mesh, how direction can be changed, and how chains and gears work together. 

Instructions:

  1. Click here to open this GearSketch simulation in your browser.

  2. Click the question mark to learn how to use the app.

  3. Create the following gear trains. After each one, click the sample answers below to see possible solutions.
    1. A fast-moving driving gear that powers two slow-moving driven gears
    2. A slow-moving driving gear that powers two fast-moving driven gears
    3. A slow-moving driving gear that connects to a gear train of two fast-moving gears and one slow-moving gear
    4. Two gears connected by a chain with a slow-moving driven gear
    5. Two gears connected by a chain with a fast-moving driven gear

Sample Solutions:

        Try It! 

      Bicycle Gears

      Try this activity to examine how bicycle gears work. 

      Materials: 
      • Multi-geared bicycle
      • Chalk or pen with white ink 

      Download:

      DOWNLOAD this document. It provides an observations table you will use later in this activity. Since this activity involves a bicycle, you may want to print out this document to take with you. It also has a place for you to answer questions at the end of the activity.

      Instructions:

      1. Switch the bicycle into high gear, with the largest gear connected to the pedals and the smallest gear connected to the back wheel.

      2. Turn the bicycle upside down so that it is balanced on its seat and handlebars.

      3. Move the pedal closest to you to its top position.

      4. Draw a chalk mark on the topmost point of the back bicycle tire, to help you count wheel revolutions.

      5. Slowly turn the pedal to make one complete revolution. As you turn the pedal, count how many revolutions the back wheel is making.

      6. When you finish making one pedal revolution, immediately use your hand to stop the back wheel from turning.

      7. Record the number of revolutions made by the back wheel. If the chalk mark is not at the top of the tire, estimate a fraction for the last revolution.

      8. Repeat steps 1 to 7 for low gear (smallest gear connected to pedal, largest gear connected to back wheel) and middle gear (pick two gears closest to the middle).

      9. Watch this video to see this experiment and its results:

       
       

      Questions: 

      Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.

      High gear would make the bicycle travel the furthest with the least amount of leg movement. High gear has a large driving gear attached to the pedals and a small driven gear attached to the back wheel. For every turn of the pedals, the small driven gear turns several times. This allows the cyclist to pedal relatively slowly, but still make the bicycle move quickly.
      If a bicycle is travelling uphill, the best combination of gears is a smaller driving gear connected to the pedals and a large driven gear connected to the back wheel. This is described as low gear. Low gear provides a force advantage, making it easier to pedal against the force of gravity with a small wheel at the pedals.
      Figure D.1.3.6– A chain connects bicycle gears.
      Figure D.1.3.7 – Pedals power the bicycle’s driving gear.


      Figure D.1.3.8 – Riding a bicycle up and down hills requires many gear changes.
      Bicycle Speeds

      Bicycles are sometimes described as having a speed, such as a 10-speed bicycle or a 21-speed bicycle. A 1-speed bicycle is sometimes called a “fixie” because the front gear and back gear are fixed together with a chain, and no other gear combinations are possible.

      Bicycle speed refers to the number of possible gear combinations that can be made with the front and back bicycle gears. For example, a 10-speed bicycle has two gears in the front and five gears in the back. Two times five equals ten different gear combinations. A 21-speed bicycle has three gears in the front and seven gears in the back.

      More combinations of gears allow cyclists to adjust to their riding conditions. Cyclists can pick a combination of gears that makes them go as fast as possible with the least amount of effort, depending on the road surface or the wind direction.

       Watch More

      Geared for Speed

      Watch this video to learn more about how bicycle gears work.

       
       

        Connections 

      Figure D.1.3.9 – A car transmission contains many gears.
      Figure D.1.3.10 – A stick shift changes the gears in a manual transmission car.


      Figure D.1.3.11 – An automatic transmission changes gears, or pulleys, depending on how the vehicle is being driven.
      Connections – Technology
      >> Transmissions

      A vehicle transmission contains gears. Transmission gears change the rotation speed of a vehicle’s engine to a different rotation speed for the vehicle’s wheels. A transmission contains multiple gears to create multiple speeds. A slower-moving car needs to connect the engine to bigger, slower-moving gears. A faster-moving car needs to connect the engine to smaller, faster-moving gears.

      In manual transmission vehicles, the driver changes the transmission gears with a stick shift and a clutch. To change gears, the driver presses down on the clutch pedal with their left foot. The clutch releases the transmission gears from their connection to the engine. The driver then moves the stick shift up or down a gear to make the transmission gears move. When the driver lifts their foot off the clutch, the car is in its new gear.

      In automatic transmission vehicles, the car has machinery which changes the transmission gears automatically. Many newer cars have a type of automatic transmission called a CVT, which stands for continuously variable transmission. A CVT uses pulleys instead of gears. CVT transmissions switch smoothly to adjust to the road conditions, which makes for a smoother ride and less wasted gas when the car changes speed.

       Watch More

      Amazing Gear Systems: Vehicle Transmissions

      Watch this video to learn more about how car transmissions work.

       
       
       
       
      Watch this video to see how a CVT works.

       
       


      Rube Goldberg Machines

      Wouldn’t it be great to put your creative talents toward something that is fun? That’s exactly what Rube Goldberg did!

      Rube Goldberg was an engineer in the early 1900’s. He quit his engineering job to draw funny cartoons for newspapers. Rube Goldberg’s comics showed designs of complex machines that accomplished a very simple task.
      To learn more about Rube Goldberg machines, click here to Explore with Elsie.



        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 3 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.

      1. DOWNLOAD the self-check quiz by clicking here.

      2. 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.

      3. 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.

      4. 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.

      5. 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.

      6. 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.

      For every turn of the large gear attached to the crank, the smaller whisk gears turn many times. The hand beater uses multiplying gears. This allows a person to use less motion of their hands to make the whisks turn very quickly.
      A can opener contains two connected Class 2 levers that open and clamp together. These levers help apply a greater force to the circular cutting wedge of the can opener. The cutting wedge pierces the metal of the can. Once the can opener is clamped to the can, the user turns a wheel and axle. The wheel and axle is connected to the circular cutting wedge, which then turns in a circle to open the entire can.
      A construction crane contains a Class 3 lever that moves upward to lift heavy loads. The end of the lever is attached to a block and tackle pulley system, which is used to lift loads with less effort.
      A car contains several subsystems. For example, the engine of a car uses gasoline or electricity to make a crankshaft rotate. The transmission of a car changes the speed of the motion from the engine’s crankshaft. The brakes of a car work to stop the car’s wheels from turning.
      An escalator is an inclined plane which reduces the effort of moving between floors. The inclined plane of an escalator is surrounded by a belt of folding stairs. The stair belt is wrapped around two large pulleys, which help move the stairs. Wheel and axle gears are connected to the pulleys. The turning motion of the wheel and axle gears drives the movement of the pulleys and the belt of stairs.