Simple Machines and Energy Transfer

Transcription

1 Science 14 Unit B: Energy Transfer Technologies Chapter 7 Simple Machines and Energy Transfer WORKBOOK Name: WEBB 2014

2 CHAPTER 7 Keeping Things in Balance BLM 7 1 SCIENCE INQUIRY Starting Point Activity Worksheet p What to Do Investigate facts that balance or bring a teeter-totter into equilibrium. Record your observations in the chart below and answer the questions that follow. Observations Mass on left = g Distance to mass from center = cm Mass x Distance = g cm Mass on Right (g) Distance to Mass on Right from Center (cm) Mass Distance (g cm) Analysis 1. How does the balanced set-up change when you double the size of the counterweight? 2. Compare the mass distance calculation for each row on the chart. A. What do you notice about the number values? B. What does this suggest about the value of mass distance? 3. Where would you need to place a 400 g mass in order to balance the meter stick? 1

3 7.1 All Kinds of Energy p Energy is the ability to do work. - There are many different kinds of energy. See Figure p Potential Energy: chemical, nuclear, elastic, gravitational - Kinetic Energy: mechanical, thermal, light, electrical Work is done when a force (push or pull) moves an object. - Calculate by multiplying the distance moved by the force used - Work can be recorded in various ways with different units - Newton-meter (N m) work done when one Newton of force is used for a distance of one meter. - Joule (J) standard way to record work. 1 J = 1 N m. Work = Force (N) x distance (m) W = F x d Simple Machines have one movement. - One example of a simple machine is the inclined plane (ramp) - Allows slide movement to go up a steep hill with less effort - Circular incline planes are used on metal bolts and bottle lids The word work has several different meanings. For example, everyday meanings of work include a place you go to make money, helping around the house, or studying at home. In physics, the word is used in a difference sense; Work is done only when both of the following occur to an object. 1) force applied 2) distance travelled i.e. Work is done when a force moves an object. - Effort does not always equal work. Example: Work is needed to lift a heavy barbell, but not to hold the barbell over your head. Both require working hard, but for work to be done the object must move. Which illustration show work being done? Discuss Figures p. 133 Discuss CYU p. 133 #1-4 2

4 Calculating Work Sample Problem: It takes about 100 N of force to push a lawn mower forward. How much work would it take if you walked 1000 m? work = force x distance Step 1: Write out the formula. W = F d W = 100 N x 1000 m Step 2: Substitute the variables with numbers values W = N m Step 3: Calculate or W = J joules of work would be done. Step 4: Summarize the final answer or put a box around it. Show all of your calculations. 1. A student is rearranging her bedroom. She decides to move her desk across the room. She exerts 200 N of force and moves the desk a total distance of 3.0 m. Calculate the amount of work done. 2. In one investigation, a student pulled a heavy block a total of 4.5 m along a wooden floor. She exerted 3.5 N of force to move the block. Calculate the amount of work done. 3. In a second investigation, a student pulled the same heavy block a total of 4.5 m over a carpeted floor. This time, it required 6.0 N of force to pull the block. Calculate the amount of work done. 4. In a third investigation, a student pulled the same heavy block a total of 4.5 m. This time, it was over a tiled floor. In this investigation, the force required to move the block was 4.5 N. Calculate the amount of work done. 5. Use your answers to questions 2, 3, and 4 to answer this question. A. Which surface required the most amount of work to move the block? B. Why do you think it took more work to move the block over this floor? 3

5 7.2 Just Prying into Things p Levers are simple machines - A bar pivots on a fulcrum to move a load (object being moved) with effort (force needed to move object) - Load Distance: fulcrum to load (A) - Effort Distance: fulcrum to effort (B) LOAD FULCRUM EFFORT A B Figure 7.12 p. 134 Three Types of levers based on the location of their parts First Class Lever fulcrum between load and effort Figure 7.13 p. 134 Example: lifting hay with a pitchfork, prying lid off paint can, and cutting FULCRUM LOAD EFFORT Second Class Lever load between fulcrum and effort Figure 7.15 p. 136 Example: moving heavy objects, bottle openers, and nutcrackers LOAD EFFORT FULCRUM 4

6 Third Class Lever effort between fulcrum and load Figure 7.16 p. 137 Example: Speed advantage - axe, badminton racket, broom, tweezers, and fishing rod EFFORT FULCRUM LOAD Discuss Figure 7.14 p. 136 Read Did You Know p. 137 Levers in Your Body Figure 7.17 p Triceps pull arm down (first class lever) - Biceps moves arm up (third class lever) Distance Multipliers move loads a large distance with a short effort distance - Commonly third class levers providing speed advantage Example: sports equipment and axes Force Multipliers easily moves a large load - Lever with a short load distance - when the effort end moves a great distance, the load moves a small distance - small force on the effort end puts a large force on the load - Commonly first and second class levers Discuss CYU p. 139 #1-6 5

7 Lever Practice Label the load, fulcrum and effort for each as well as identify the lever type. 6

8 7.3 Wheels, Pulleys, and Blocks p Pulley simple machine with a rope or chain threaded around a grooved wheel - effort can support the load at equilibrium - Similar to a Class 1 lever in that the bar of the lever is like the rope, the axle of the pulley is the fulcrum, and the two sides of the pulley are the effort and load arms. - Single pulleys are used to change the direction of effort Example: flag pole, clothesline, adjust curtains fixed pulley stationary wheel and load force equals effort force - Figure 7.19 p. 142 movable pulley move load attached to wheel Read Career Connect p. 142 Wheel and Axle simple machine with two turning objects attached at their centers - larger object causes the other to turn providing mechanical advantage Example: screwdriver, winch, door knob, and wrench (Figure 7.21 p. 143 ) - a winch is a small cylinder and a crank or handle. - Similar to a lever, except it keeps turning - stationary axle acts like a fulcrum and the handle is the effort arm that turns the wheel when a force is applied - wheel radius (center to outside) is like the load arm while the load is attached to the cable and exerts force on the wheel - Since the handle is much longer than the radius of the wheel, the effort force is smaller than the load. Discuss CYU p. 144 #1-5 7

9 7.4 Spinning Our Wheels: Energy and Efficiency p Using a simple machine like an inclined plane makes the job easier but it takes more work to lift an object the same height because it requires a longer distance to complete the task - Machines lose energy through: - Friction between any moving parts creating thermal energy - Heat released by the cooling system or through exhaust - Incomplete combustion doesn t use all the stored chemical energy in the fuel Efficiency compares the work a machine does with the energy it uses to do that work - With loss of energy, mostly to heat, no machine is 100% efficient i.e. the work output does not equal the work input - work input is always greater than useful work output Example: only a fraction of the heat from a stove burner is used to cook food, the rest is lost by convection currents to the surrounding air - the cost of energy continues to increase - efficiency is a way to conserve energy and money as well as help the environment - electric appliances tend to be more efficient than gasoline engines Discuss Table 7.1 p. 146 (Efficiency of Common Technology) - EngerGuide Number - average annual energy use rating Figure 7.4 p Large amounts of energy are measured in units of kilowatt hours (kw h) - Represents the amount of electricity from 1000 watts used for one hour Example: 100 watt bulb burning for 10 hours uses 1 kw h of energy - One kilowatt hour equals a little more than 3.5 million joules Complete Investigation 7C p #1-2 Helping the Environment: - Canada s primary source of energy is burning fossil fuels, which are a non-renewable resource and contribute to global climate change as well as air pollution Discuss Figures pp (ideas for conserving energy) Discuss CYU p. 149 #1-4 Complete Chapter 7 Review Questions p #1-9 8

10 Energy & Simple Machines Crossword Complete the crossword using the clues provided. Across 1. ability to do work 6. the object being moved 8. The load is in the middle of a class lever. 9. another word meaning balance 13. unit of work 14. A pulley that doesn t rise and fall as load moves 15. There are three classes of this simple machine. 16. a grooved wheel on an axle 19. in the middle of a third class lever 20. distance between the load and fulcrum 23. A pulley that rises and falls as the load moves 24. unit of electricity work output 25. = 100 work input 26. A force moves a large load with little effort. Down 2. the distance between the effort and fulcrum 3. unit of energy 4. effort applied to a machine 5. another term that means heat energy 7. in the middle of a first class lever 10. When the sides of a lever are equal 11. a simple machine with no moving parts 12. number of movements in a simple machine 17. A machine that moves a load through a great distance with little effort is a multiplier. 18. a push or pull 21. the product of effort over a distance 22. common example of a wheel and axle you can ride 9

11 Chapter 7 Review Questions 1. Explain the type(s) of energy involved when a bungee jumper jumps. (7.1) 2. Name four different types of energy. (7.1) 3. What is required to calculate work? (7.1) 4. What will happen when the angle of a ramp is increased? (7.1) 5. Name and explain the location of the parts of a playground teeter-totter. (7.2) 6. Use a chart to summarize the differences between the three classes of lever. (7.2) Class of Lever Middle Part Multiplies Effect on Direction First Second Third 7. Give two examples of your body acting as a lever. (7.2) 8. Name two examples of a distance multiplier. (7.2) 10

12 9. Name two examples of a force multiplier. (7.2) 10. As you increase the number of pulleys used, is more or less effort needed? (7.3) 11. List four simple machines that use the wheel and axle. (7.3) 12. Using an example, explain the location of the five parts of a pulley. (7.3) 13. How is energy use measured around the home? (7.4) 14. Where would you find an Energuide Number and what does it tell you? (7.4) 15. List three ways to reduce energy consumption. (7.4) 16. What is the purpose of insulation in a home? (7.4) 11