SCIENCE 8. Unit 4 Booklet. Machines and Mechanical Systems

Transcription

1 SCIENCE 8 Unit 4 Booklet Machines and Mechanical Systems

2 TOPIC 1 REINFORCEMENT Levers Have Class BLM 4-2 Goal Identify items as Class 1, Class 2, or Class 3 levers. Introduction There are three classes of levers. In a Class 1 lever, the fulcrum is between the effort and the load. In a Class 2 lever, the resistance is between the effort and the load. A Class 3 lever is arranged so that the effort is between the load and the fulcrum. To use a Class 3 lever, you must exert a greater force on the lever than the lever exerts on the load. The advantage is that the load can be moved very quickly. What to Do Identify the class of each lever below. Copyright 2001, McGraw-Hill Ryerson Limited, a Subsidiary of the McGraw-Hill Companies. All rights reserved. Permission to edit and reproduce this page is granted to the purchaser for use in his/her classroom only. McGraw-Hill Ryerson Limited shall not be held responsible for content if any revisions, additions, or deletions are made to this page.

3 TOPIC 1 PROBLEM SOLVING What is Work? BLM 4-3 Goal Practice using and applying the scientific definition of work to everyday situations. 1. Fill in the blanks below. Work = Force x Distance (a) 100 J = x 1 m (b) 100 J = x 2 m (c) 100 J = x 5 m (d) 100 J = x 10 m (e) 100 J = x 50 m (f) 100 J = x 100 m 2. In each case above the work done was the same (100 J). However, the amount of force needed to do the work changed. (a) The easiest way to do the work was in example because (b) The fastest way to do the work was in example because 3. Vivian and Christy were having a tug-of-war with their gym teacher. The distance to pull was 3 m. They pulled as hard as they could, but they could not move him! Assuming the teacher s mass is 90 kg and Vivian and Christy pulled with force of 800 N, how much work did they do? Show your calculation. 4. Smiley Joe s Garage uses a block and tackle style pulley to help lift engines out of customer s cars for repairs. One customer s engine has a mass of 221 kg. To lift the engine out entirely, Smiley Joe has to raise it 1.5 m. How much work will he do? Show your calculation. Copyright 2001, McGraw-Hill Ryerson Limited, a Subsidiary of the McGraw-Hill Companies. All rights reserved. Permission to edit and reproduce this page is granted to the purchaser for use in his/her classroom only. McGraw-Hill Ryerson Limited shall not be held responsible for content if any revisions, additions, or deletions are made to this page.

4 TOPIC 1 PROBLEM SOLVING What is Work? (continued) BLM A student decides to use ramp B to move a case of juice into the school. Use the diagram below to explain why she probably made her choice. Explain why the amount of work done to lift her load would remain the same no matter which ramp she chose. 6. To assist with a class demonstration, a student (whose mass is 60 kg) filled a water balloon with 2 kg of water. He then climbed to the second floor of the school and held the balloon out of a window. How much work did the student do? 7. With the class watching from a safe (and dry!) distance below, suppose the student drops the balloon and the balloon hits the sidewalk with a force of 20 N. How much work was done on the sidewalk by the balloon? Copyright 2001, McGraw-Hill Ryerson Limited, a Subsidiary of the McGraw-Hill Companies. All rights reserved. Permission to edit and reproduce this page is granted to the purchaser for use in his/her classroom only. McGraw-Hill Ryerson Limited shall not be held responsible for content if any revisions, additions, or deletions are made to this page.

5 TOPIC 1 PROBLEM SOLVING What is Work? (continued) BLM Do you get a better workout by jumping or doing pushups? Use what you know about work to figure it out. (a) Your mass = kg. This is equivalent to N (force). Have a friend measure how high you can jump in centimetres. cm Covert that figure to metres. = m How much work do you do in one jump? (b) Repeat the above process using a push-up. (c) Using your results, explain whether you think jumping or doing pushups is the better workout. Copyright 2001, McGraw-Hill Ryerson Limited, a Subsidiary of the McGraw-Hill Companies. All rights reserved. Permission to edit and reproduce this page is granted to the purchaser for use in his/her classroom only. McGraw-Hill Ryerson Limited shall not be held responsible for content if any revisions, additions, or deletions are made to this page.

6 TOPIC 2 REINFORCEMENT Pulley Power BLM 4-9 Goal Review the different types of pulleys and their mechanical advantage. Introduction A pulley is a grooved wheel with a rope or a chain running along the groove. A pulley does not do work for you, but it makes work easier by changing the direction in which you apply effort (pulling down is easier than lifting) or by giving you a mechanical advantage. The larger the mechanical advantage is, however, the longer the distance over which the work must be done. What to Do Answer the following questions in the space provided. 1. Study each diagram below, and complete the sentences at the right. (a) There is a/are fixed pulley(s). There is a/are moveable pulley(s). This combination has a mechanical advantage of. (b) There is a/are fixed pulley(s). There is a/are movable pulley(s). This combination has a mechanical advantage of. Copyright 2001, McGraw-Hill Ryerson Limited, a Subsidiary of the McGraw-Hill Companies. All rights reserved. Permission to edit and reproduce this page is granted to the purchaser for use in his/her classroom only. McGraw-Hill Ryerson Limited shall not be held responsible for content if any revisions, additions, or deletions are made to this page.

7 TOPIC 2 REINFORCEMENT Pulley Power (continued) BLM 4-9 (c) There is a/are fixed pulley(s). There is a/are movable pulley(s). This combination has a mechanical advantage of. (d) There is a/are fixed pulley(s). There is a/are movable pulley(s). This combination has a mechanical advantage of. 2. Design a pulley system (block and tackle) that uses two fixed and two movable pulleys. Draw your design here. Copyright 2001, McGraw-Hill Ryerson Limited, a Subsidiary of the McGraw-Hill Companies. All rights reserved. Permission to edit and reproduce this page is granted to the purchaser for use in his/her classroom only. McGraw-Hill Ryerson Limited shall not be held responsible for content if any revisions, additions, or deletions are made to this page.

8 TOPIC 3 PROBLEM SOLVING Efficiency Calculations BLM 4-10 Goal Review how to calculate the efficiency of various simple machines. Introduction An ideal machine would transfer all of the energy it received to a load or to another machine, giving it an efficiency of 100 percent. Real machines, however, do not work this efficiently. Some energy is always lost. Heat, friction, and noise are three ways that energy is lost. What to Do Use the formulas below to solve the following problems. Show your calculations. Efficiency = Work done by a machine on a load Work done on a machine by an effort force x 100% Work in joules (J) = Force (N) x Distance (m) 1. The work done by a ramp is 1430 N m or 1430 joules (J). The work done by the effort force is 1650 J. What is the efficiency of the machine? 2. The work done by a lever is 5675 J. The work done by the effort force is J. What is the efficiency of the machine?.

9 TOPIC 3 PROBLEM SOLVING Efficiency Calculations (continued) BLM The girl in the following diagram wants to raise a cart that weighs 350 N to a height of 4 m. If she uses a ramp, she needs to pull the cart 10 m using a force of 160 N. If she lifts the cart without a ramp, she needs to exert a force of 350 N for 4 m. What is the efficiency of the ramp? 4. (a) Why is a machine never 100 percent efficient? (b) What could be done to increase the efficiency of the ramp in question 3? Introduction Mechanical advantage (MA) compares the force that is produced by a machine (the load) with the force that is applied to the machine (the effort force). Mechanical advantage indicates how much a machine can increase or decrease the force on a load, compared with the effort force. The figure for mechanical advantage does not require a unit. What to Do Use the formula below to solve the following problems. Show your calculations. MA = Load Force (F L ) Effort Force (F E ) 1. You are a passenger in a truck that gets stuck in mud. You and the driver use a tree branch as a lever to lift up the truck. You apply an effort force of 600 N to the branch. The back of the truck weighs 2400 N. What is the mechanical advantage of the branch-lever? 2. Suppose that you are riding a bicycle. You exert an effort force of 697 N downward as you push on the pedals. The resulting load force that causes the bicycle to move forward is 93 N. What is the mechanical advantage of the bicycle?.

10 3. Two people use a ramp to move a heavy box onto a truck. The box weighs 750 N. The mechanical advantage of using the ramp is 4. How much effort is required to move the box? 4. A pulley is used to raise a bucket that weighs 60 N. How much effort is required if the mechanical advantage is 1? DATE: NAME: CLASS: TOPIC 4 REINFORCEMENT Pascal s Law and Mechanical Advantage Goal Review Pascal s law and the calculation of mechanical advantage. BLM 4-16 Think About It Blaise Pacal was a French doctor and scientist who lived in the mid-seventeenth century. He made some significant observations about fluid and pressure. He noticed that the shape of a container had no effect on pressure. He also noticed the following: If a vessel of water, otherwise completely closed, has two openings, one of which is one hundred times as large as the other; by putting in each of these a piston which fits it exactly, a man pushing on the small piston will exert a force equal to that of one hundred men pushing on the piston which is one hundred times as large, and will overcome that force of ninety-nine men. Pascal s observation is true for one hundred women or one hundred children as well! His point has come to be known as Pascal s law. When applied in a real situation, Pascal s law can be used to great mechanical advantage. What to Do Use the formulas below to solve the following problems. Show your calculations. P (Pa) = F (N) A (unit area) W (N m or J) = F (N) x d (m) Mechanical advantage = Load force (N) Effort force (N) 1. Suppose that you are able to exert a force of 300 N on the piston of a hydraulic lift. The piston has an area of 64 cm 2. What does the area of the other plunger have to be if you want to lift a load of 200 N?.

11 2. A system requires you to exert a force of 20 N in order to lift a load of 120 N. What is the mechanical advantage of this system? 3. Suppose that you want to lift a 120 N load a distance of 2 m using the system in question 2. Approximately how far do you have to push the piston as you exert your pressure force? Going Further 4. Illustrate what Pascal was describing in the quotation at the beginning of this exercise. Draw your idea in the space below. Is his law easier to understand in a picture? DATE: NAME: CLASS: TOPICS 7-8 ASSESSMENT Topics 7-8 review What to Do Carefully read the instructions before answering each set of questions. Fill in the Blanks Complete the paragraph with the correct terms. James (1) created the (2) engine, which was used to power locomotives. Steam is the (3) that is produced when water is boiled. In a steam engine, fuel such as (4) or (5) is burned to heat water in a boiler outside the engine. The steam that is produced drives a (6) up and down, which sets other parts in motion to move the wheels of the locomotive. BLM 4-29 As well as powering locomotives, steam engines moved (7) along rivers. Today steam still powers ocean liners. Instead of driving pistons up and down in an ocean liner, however, the steam turns large (8). The fan blades on a turbine (9) when steam moves past them at high speed. This turns giant (10) that drive the ocean liner through the water..

12 Multiple Choice Circle the letter for the best answer. 11. Which of these actions does not occur in a steam engine? (a) Steam expands and pushes the piston down. (b) Exhaust valves open to allow steam to escape. (c) Steam expands and pushes the piston up. (d) Coal or wood is burned by a boiler inside the piston. 12. Which of these parts does not belong to a steam turbine? (a) stationary blade (b) axle (c) piston (d) turbine wheel 13. Which of these parts does not belong to an internal combustion engine? (a) intake valve (b) cylinder (c) aileron (d) piston 14. Which of the following is not an example of mass production? (a) home appliances produced in a factory (b) the canning of foods in a food-processing plant (c) a person weaving a rug on a loom (d) the production of automobiles in an assembly plant Short Answers Answer each question briefly in the space provided. 15. Throughout the last century, automobiles went through many changes in design. Discuss at least two reasons why automobile designs changed. 16. Does society change technology, does technology change society, or do both happen? Use one specific example to explain your answer..