Skills Worksheet Directed Reading A Section: Types of Machines 1. A knife is actually a very sharp. 2. What are the six simple machines that all other machines are made from? LEVERS 3. A simple machine with a bar that pivots at a fixed point is a(n) a. wedge. c. knife. b. lever. d. screw. 4. What is the fixed point on a lever? a. bolt c. fulcrum b. pivot point d. wedge 5. What do first-class levers always change the direction of? a. input force c. distance b. output force d. fulcrum 6. When you use the claw of a hammer to remove a nail, what type of simple machine are you using? a. wedge c. second-class lever b. first-class lever d. third-class lever 7. What three things are present with each class of lever? 8. Describe the three classes of levers and give an example of each. Holt Science and Technology 7 Work and Machines
Directed Reading A continued 9. In a second-class lever, why must you exert input force over a greater distance? 10. Why is the output force always less than the input force in a third-class lever? PULLEYS 11. Which simple machine has a grooved wheel that holds a rope or cable? a. lever c. pulley b. wedge d. wheel and axle 12. Which pulley is attached to something that does not move? a. fixed pulley c. block and tackle pulley b. movable pulley d. simple pulley 13. Which type of pulley is attached to the object being moved? a. fixed pulley c. block and tackle pulley b. movable pulley d. simple pulley 14. What determines the mechanical advantage of a block and tackle pulley? a. the amount of input force b. the amount of output force c. the length of the rope d. the number of rope segments 15. Why does a fixed pulley provide only a mechanical advantage of 1? How does this type of pulley affect the force? 16. How does a movable pulley increase the output force? 17. How does a block-and-tackle multiply the input force? Holt Science and Technology 8 Work and Machines
Directed Reading A continued WHEEL AND AXLE 18. What type of simple machine is a faucet? a. lever c. wheel and axle b. pulley d. wedge 19. What does a wheel and axle consist of? 20. How do you find the mechanical advantage of a wheel and axle? INCLINED PLANES 21. When you use a ramp to move an object, what type of simple machine are you using? a. lever c. pulley b. inclined plane d. wedge 22. A wedge is what type of simple machine? a. pulley c. inclined plane b. lever d. wheel and axle 23. Which of the following is an inclined plane wrapped in a spiral around a cylinder? a. screw b. wedge b. nail d. ramp 24. A jar lid is an example of which simple machine? a. nail b. wedge b. screw d. ramp 25. A simple machine that has a straight, slanted surface is a(n). 26. A simple machine that is made up of two inclined planes and moves is a(n) 27. How do you find the mechanical advantage of an inclined plane? Holt Science and Technology 9 Work and Machines
Directed Reading A continued 28. Why does a sharpened knife cut better? 29. What two factors determine the mechanical advantage of a screw? COMPOUND MACHINES 30. When two or more simple machines are combined, they make a(n). 31. What three simple machines make up a can opener? 32. Why is the mechanical efficiency of most compound machines lower than most simple machines? 33. Name two compound machines. 34. Why is it important to reduce friction on compound machines? Holt Science and Technology 10 Work and Machines
TEACHER RESOURCE PAGE Answer Key Directed Reading A SECTION: WORK AND POWER 1. C 2. A 3. Answers will vary. Sample answer: Carrying a book across a room is not work because the book is not moving in the direction of the force. 4. The object moves as a force is applied to it and the direction of the object s motion is the same as the direction of the force. 5. kinetic 6. Because work depends upon distance and force. The straight cliff is a shorter distance but takes more force. The slope is a longer distance, but takes less force. 7. force (F), distance (D) 8. joule 9. energy 10. weight and distance 11. B 12. C 13. Power measures how fast work happens or how quickly energy is transferred 14. Power output is greater when more work is done in a given amount of time and when the time it takes to do a certain amount of work is decreased. 15. The power output is lower when you sand the shelf by hand. 16. A more powerful engine will move the car more quickly. For a given speed, a more powerful engine can move a heavier car than a less powerful engine can. 17. A joule is a unit to express energy. One watt is equal to 1 joule per second. SECTION: WHAT IS A MACHINE? 1. A 2. C 3. work input 4. work output 5. Work input is the work done on a machine, such as when you push on the screwdriver to pry the paint can lid off. Work output is the work done by the machine such as the screwdriver lifting the paint can lid. Students examples may vary. 6. Sample answer: scissors and chopsticks 7. increases 8. input force 9. The amount of work for each is the same. 10. distance 11. Machines make work easier by changing the size or direction of the input force. But the amount of work done is the same. 12. C 13. B 14. greater 15. distance 16. B 17. D 18. input 19. friction 20. A machine that is 100% efficient. 21. Machines aren t 100% efficient because some of the machine s work input is used up by the friction from moving parts. 22. Magnets and lubricants can help reduce friction. SECTION: TYPES OF MACHINES 1. wedge 2. lever, inclined plane, wedge, screw, pulley, wheel and axle 3. B 4. C 5. B 6. B 7. fulcrum, bar, load Holt Science and Technology 100 Work and Machines
TEACHER RESOURCE PAGE 8. Answers will vary. Sample answer: In a first-class lever, the fulcrum is between the input force and the load;. hammer lifting up nail. In a secondclass lever, the load is between the fulcrum and the input force; wheel barrow, bottle opener. In a third-class lever, the input force is between the fulcrum and the load; hammer pounding nail. 9. Because the output force is greater than the input force. 10. Because they do not change the direction of the force and they do not increase input force. 11. C 12. A 13. B 14. D 15. Distance through which the forces are exerted and the forces themselves are the same.this pulley changes the direction of the force. 16. Because the movable pulley moves up with the load as the load is lifted. 17. It multiplies the input force by increasing the distance through which the load moves. 18. C 19. two circular objects of different sizes 20. Divide the radius of the wheel by the radius of the axle. 21. B 22. C 23. A 24. B 25. inclined plane 26. wedge 27. Divide the length of the inclined plane by the height to which the object is lifted. 28. The knife is thinner and longer, which increases its mechanical advantage. 29. the length of the spiral on the screw and how close together the threads are. 30. compound machine 31. second-class lever, wedge, wheel and axle 32. Because there are more moving parts causing more friction 33. Answers will vary. Sample answer: a hand can opener and a block and tackle pulley 34. Too much friction can damage the simple machines that make up the compound machine. Directed Reading B SECTION: WORK AND POWER 1. C 2. A 3. C 4. energy 5. direction 6. force 7. D 8. distance 9. push 10. force 11. C 12. A 13. D 14. B 15. power 16. watt 17. time 18. output SECTION: WHAT IS A MACHINE? 1. D 2. C 3. machine 4. input 5. output 6. greater 7. A 8. B 9. B 10. D 11. A 12. D 13. friction 14. ideal machine 15. oil SECTION: TYPES OF MACHINES 1. C 2. B 3. C 4. A 5. C 6. B 7. A 8. C 9. A 10. B Holt Science and Technology 101 Work and Machines