Critical Thinking
Applying Concepts Give an example of a useful machine you have seen that has a mechanical advantage less than 1. State how the machine is useful in terms of changing forces, distances, or directions.
Comparing and Contrasting A ramp 20 m long and 4 m high is used to lift a heavy box. A pulley system with 4 rope sections supporting the load is used to lift an identical box to a height of 4 m. Assume that friction can be ignored. Compare and contrast the input force and input distance needed to lift each box.
Generalizing In a pulley system, where is there likely to be friction that reduces the efficiency?
Classifying Classify each of these items as a type of simple machine: a steel bolt, an iron nail, and a screwdriver.
Math Skills
Use the illustration below to answer Questions 26 and 27.
Using Equations The figure above shows the distances from the fulcrum to the input and output forces of a lever. Use these distances to calculate the ideal mechanical advantage of the lever.
Using Equations If the actual mechanical advantage is 2.9 and the input force is 10.0 N, what is the output force?
Using Equations How much work does a 50-N force do when lifting a box 2 meters?
Calculating How much work does a 1-kW motor do in one minute?
Concepts in Action
Applying Concepts Which would be the better choice for driving a screw into a board, a long screwdriver with a narrow handle, or a short screwdriver with a wide handle? Explain.
Classifying What type of simple machine is a water faucet handle? Is the output force larger or smaller than the input force?
Comparing and Contrasting A man weighing 1000 newtons walks from the ground floor to the fifth floor of a building, gaining 20 meters of height in 200 seconds. The next day he returns to the building, but this time uses the elevator. The elevator takes 20 seconds to reach the fifth floor. Compare and contrast the power and time requirements to reach the fifth floor.
Relating Cause and Effect In a bicycle, the output of one simple machine is the input of another. Why might you expect the efficiency of the bicycle to be less than the efficiency of each of the simple machines that is part of it?
Writing in Science Explain why you might shift into a lower gear to climb a hill on a bike. Your explanation should include a discussion of the input force and distance.
Performance-Based Assessment
Using Models Imagine you have a younger brother who weighs half as much as you do. Design a seesaw you could use together. Create a model of your seesaw design and label it to show the distances that you and your brother must sit from the fulcrum. Explain why you chose the fulcrum position as you did.
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