Ch14.2 Work and Machines – Flashcards
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Machine
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is a device that changes a force.
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Input distance
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the distance the input force acts through.
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Output force
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the force that is exerted by a machine.
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Work output
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is the output force multiplied by the output distance.
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Input force
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the force you exert on a machine.
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Work input
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the work done by the input force acting through the input distance.
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Output distance
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the distance the output force is exerted through.
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Does the jack used to lift the car increase or decrease the force applied to it? Look at Figure 5.
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The jack increases the force applied to it.
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How does the force exerted on the jack handle compare with the force exerted by the jack on the car? Look at Figure 6.
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The force exerted on the jack handle is much less than the force exerted by the jack on the car.
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If the oar is pushed farther away from the boat, how will the force needed to pull the oar through the water change? Look at Figure 7.
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The required input force would increase.
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Give an example of a machine that changes the direction of an applied force.
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A jack changes the direction of the applied force because the input force is circular and the output force is vertical. Other examples include a crowbar, a seesaw, and a pulley.
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What evidence can you see in the photo that a force is acting on the water? Look at Figure 8.
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The movement of the water indicates that a force is acting on it.
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How can using a machine make a task easier to perform?
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Machines make work easier to do by altering the size of force needed, the direction of a force, or the distance over which a force acts.
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How does the work done on a machine compare to the work done by a machine?
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Because of friction, the work done by a machine is always less than the work done on the machine.
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What changes can a machine make to a force?
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Size of force; direction of force; distance through which a force acts.
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A machine produces a larger force than you exert to operate the machine. How does the input distance of the machine compare to its output distance?
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Because the output force is greater than the input force, the input distance must be greater than the output distance.
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You do 200 J of work pulling the oars of a rowboat. What can you say about the amount of work the oars do to move the boat? Explain.
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Less than the 200 J of work are done to move the boat because some of the input work is lost to friction forces.
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How can you increase the work output of a machine?
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Increase the work input to the machine, or reduce any friction that limits work output.
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When you swing a baseball bat, how does the output distance the end of the bat moves compare with the distance you move your hands through? Why might this difference be useful?
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The output distance is much greater than the input distance. The high speed of the bat end helps the batted ball to also acquire a high speed (and travel far).
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An advertisement for a new type of wrench claims it reduces the force needed to tighten a bolt. If the advertisement is correct, what do you know to be true about the input distance?
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If the input force is decreased, then the input distance must be increased.
