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Define the following terms A. Work B. Power C. Machine

S-34. Define the following terms A. Work B. Power C. Machine. SPS8 Students will determine relationships among force, mass, and motion. e. Calculate amounts of work and mechanical advantage using simple machines. Chapter 14 Work, Power, and Machines. When does a force do work?

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Define the following terms A. Work B. Power C. Machine

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  1. S-34 • Define the following terms • A. Work • B. Power • C. Machine

  2. SPS8 Students will determine relationships among force, mass, and motion. e. Calculate amounts of work and mechanical advantage using simple machines Chapter 14 Work, Power, and Machines

  3. When does a force do work? How are work and power related? 14.1 Work and Power

  4. 12.1 Force Force Force displacement displacement displacement Force 14.1 Work and Power When does a force do work?? Work Done No Work Done Work – force applied over a distance For work to be done force must act in the same direction as the movement Any part of the force that doesn’t point in the direction of motion doesn’t do any work

  5. 12.1 Force 14.1 Work and Power When does a force do work?? W=Fd The equation for work is W=work in joules F = force in newtons d = distance in meters The unit is the same as energy because work is the transfer of energy

  6. 12.1 Force 14.1 Work and Power When does a force do work?? W=(72N)(3m) W=216J W=Fd F=72 N d=3 m Practice Work Problem 1 A vertical force of 72 N is used to lift a box to a height of 3.0 m. How much work is done? Variables? Fill in Equation Answer

  7. 12.1 Force 14.1 Work and Power When does a force do work?? 302J=(25N)d d=12.08m W=Fd F=25 N W=302J Practice Work Problem 2 A force of 25 N does 302 J of work. How far did the object get pushed? Variables? Fill in Equation Answer

  8. 12.1 Force 14.1 Work and Power How are work and power related? • Power is the rate of doing work. • For something to be more powerful, it must • Do more work in the same period of time • Do the same amount of work faster

  9. 12.1 Force 14.1 Work and Power When does a force do work?? P=W/t • The equation for power is • P = power in watts • W = work in joules • t = time in seconds • Power is sometimes measured in horsepower, 1 HP = 746W

  10. 12.1 Force 14.1 Work and Power When does a force do work?? P=(216J)/(2s) P=108W P=W/t W=216J t=2.0s Practice Power Problem 1 216 J of work are done to lift a box in 2.0s. How much power is needed to lift the box? Variables? Fill in Equation Answer

  11. 12.1 Force 14.1 Work and Power When does a force do work?? 79822W=(1173)/t t=0.015s P=W/t P=79822W W=1173J Practice Power Problem 2 If an engine can generate 79822 W of power, how long would it take to do 1173 jof work? Variables? Fill in Equation Answer

  12. S-35 How are work and power related? • During the worlds strongest man competition, this man moved a 20,000-N truck a distance of 12-m in 60-s. • A. How much work did he do. • B. How much power did he generate?

  13. How do machines make work easier? How are work input and work output related for a machine? 14.2 Work and Machines

  14. 12.1 Force 14.2 Work and Machines How do machines make work easier? • Machine – a device that changes force • Change the size of a force • Change the direction of a force • Increase force by increasing the distance • Decrease force by decreasing the distance

  15. 12.1 Force 14.2 Work and Machines How do machines make work easier? • Definitions • Input force – the force you exert on a machine • Output force – the force exerted by the machine • Input distance – how far you move the machine • Output distance – the distance that the machine move the object • Work input – the input force x input distance • Work output – the output force x output distance

  16. 12.1 Force 14.2 Work and Machines How are work input and work output related for a machine? In a perfect machine – work input would equal work output But because of friction – the work output is ALWAYS less than the work input

  17. How does the actual mechanical advantage of a machine compare to its ideal mechanical advantage? Why is the efficiency of a machine always less than 100 percent? 14.3 Mechanical Advantage and Efficiency

  18. 12.1 Force 14.3 MA & Efficiency How does the AMA of a machine compare to its IMA? Mechanical Advantage – the number of times that the machine increases input force Actual Mechanical Advantage – the ratio of output force to input force

  19. 12.1 Force 14.3 MA & Efficiency How does the AMA of a machine compare to its IMA? Output Force=200 N Input Force=25 N Sample Problem A lever is used to lift a heavy weight. The weight is 200-N, and a force of 25 N is required to lift it. What is the Actual Mechanical Advantage? Variables? Fill In? Answer?

  20. 12.1 Force 14.3 MA & Efficiency How does the AMA of a machine compare to its IMA? Idea Mechanical Advantage – the mechanical advantage in the absence of friction Because of friction, the IMA is always greater than the AMA A ratio of the input distance to the output distance

  21. 12.1 Force 14.3 MA & Efficiency How does the AMA of a machine compare to its IMA? Input Dis.=1.8m Output Dis.=0.3m Sample Problem A woman drives her car up onto wheel ramps to perform some repairs. If she drives a distance of 1.8 m to raise the car 0.3 m, what is the IMA of the ramp? Variables? Fill In? Answer?

  22. S-36 How does the actual mechanical advantage of a machine compare to its ideal mechanical advantage? • A man uses a crowbar to break off a 40,000 N piece of rock. The rock moves a total distance of 0.08 m. The man pushes on the crowbar with a force of 4050 N while pushing the crowbar 0.80 m. • A. What is the AMA of the crowbar? • B. What is the IMA of the crowbar?

  23. S-37 How does the actual mechanical advantage of a machine compare to its ideal mechanical advantage? A girl cranks an ice cream churn by pushing on the handle with 25 N of force. The churn applies a force of 95 N. When the crank turns 1 complete circle, the ice cream spins 0.25 turns A. What is the AMA of the churn? B. What is the IMA of the churn?

  24. 12.1 Force 14.3 MA & Efficiency Why is the efficiency of a machine always less than 100 percent? Efficiency – the percentage of work input that becomes work output

  25. 12.1 Force 14.3 MA & Efficiency Why is the efficiency of a machine always less than 100 percent? Win=(25N)(45) Win=1125J W=Fd Wout=(200N)(5m) Wout=1000J W=Fd A pulley system is set up to lift a 200-N box. The box is lifted 5 m when a force of 25 N is applied over a distance of 45 m. 1. What is the work input? 2. What is the work output? 3. What is the efficiency of the machine?

  26. What are the six types of simple machines? 14.4 Simple Machines

  27. 12.1 Force 14.3 MA & Efficiency What are the six types of simple machines? • Lever – a rigid bar free to move around a fixed point

  28. 12.1 Force 14.3 MA & Efficiency What are the six types of simple machines? • Wheel and Axle – two disks or cylinders, with different radii

  29. 12.1 Force 14.3 MA & Efficiency What are the six types of simple machines? • Inclined Planes – a slanted surface

  30. 12.1 Force 14.3 MA & Efficiency What are the six types of simple machines? • Wedges and Screws are moving inclined planes • Wedge – V shaped object

  31. 12.1 Force 14.3 MA & Efficiency What are the six types of simple machines? • Screw – inclined plane wrapped around a cylinder

  32. 12.1 Force 14.3 MA & Efficiency What are the six types of simple machines? • Pulley – a rope that fits into a groove in a wheel

  33. 12.1 Force 14.3 MA & Efficiency What are the six types of simple machines? • Compound Machine – a combination of two or more simple machines

  34. S-38 Why is the efficiency of a machine always less than 100 percent? • A man uses a crowbar to break off a 40,000 N piece of rock. The rock moves a total distance of 0.08 m. The man pushes on the crowbar with a force of 4050 N while pushing the crowbar 0.80 m. • What is the efficiency of the crowbar?

  35. S-39 Why is the efficiency of a machine always less than 100 percent? • Bob has a job pulling out nails. It is not a very exciting job. When Bob applies a force of 5.5-N to his hammer, the nail move 0.03 m with a force of 25 N. Bob has to move the hammer 0.15 m. • A. What is the AMA of the hammer? • B. What is the IMA of the hammer? • C. What is the efficiency of the hammer?

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