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Chapter 8

Chapter 8. Work and Machines. the action that results when a force causes an object to move in the direction of the force. Work : ___________________________________________________________ ________________________________________________________________. Ex: Pushing a shopping cart.

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Chapter 8

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  1. Chapter 8 Work and Machines

  2. the action that results when a force causes an object to move in the direction of the force Work: ___________________________________________________________ ________________________________________________________________ Ex: Pushing a shopping cart in the same Work is ONLY being done when the object moves ____ _____ _________ _____________________ as the force that is acting upon it. In order for work to be done, the object must: 1. _______________ 2. _____________________________________ direction move in the same direction as the force

  3. F x d The mathematical formula for work is W = _____________ where F = _______________ acting upon the object and d = __________________ that the object is moved. The unit used to measure work is _________________ which is equal to a ____________ ___________. the force the distance joule (J) Newton - meter (N.m) Example: A man applies a force of 500 N to push a truck 100 m down the street. How much work does he do? ________________________________________ W = F x d = 500 N x 100 m = 50,000 J Example: In which situation do you do more work? A. You lift a 75 N bowling ball 2 m off the floor. B. You lift two 50 N bowling balls 1 m off the floor. W = 75N x 2m = 150J W = 100N x 1m = 100J Power: ________________________________________________________The mathematical formula for power is P = ______ or power = _________ the rate at which work is done (how fast work is done) W t work time The unit used to measure power is the ________________ which is equal to _____________________. watt (W) joules per second (J/s) Example: What is the power of a small motor that can do 4500 J of work in 25 seconds? _________________________________________________ P = W/t = 4500 J / 25 s = 180 W

  4. Machines A machine is a device that ________________________________________ ______________________________________________________________ Examples of simple machines are __________________________________ ______________________________________________________________ Input work: _____________________________________________________ ______________________________________________________________ Output work: ____________________________________________________ _______________________________________________________________ **** ________________ can NEVER be greater than ____________________! helps make work easier by changing the size or direction (or both) of a force. scissors, screw drivers, screws, jacks, ramps, pulleys, crowbars the work you do on a machine when your input force moves the machine through a distance the work done by the machine when the machine applies an output force through a distance. Work output work input When the size of the ______________ is changed, the________________ through which the force acts must also change. They are inversely related: when the force _________________, the distance _________________ and when the force _________________, the distance __________________. Using machines does NOT change the amount of work done!!! force distance increases decreases decreases increases

  5. Mechanical Advantage: _________________________________________________________________________________________________________ This can be calculated by: MA = ___________________________ a number that tells how many times a machine multiplies force output force input force Which has a greater mechanical advantage, a machine to which you apply a force of 50 N and the machine applies a force of 150 N, or a machine to which you apply a force of 60 N and the machine applies a force of 200 N? First machine: ________________________________________________ Second machine: _____________________________________________ 150 N / 50 N = 30 N 200 N / 60 N = 3.3 N The larger the _____________ ______________, the easier the machine makes it to do the work. BUT the ___________________ that the output force moves the object ___________________. mechanical advantage distance decreases Work output is always _______ than work input. This is because work must always overcome the force of _________________. Work input is _________ work output plus the work done to overcome the force of friction. less friction equal to Mechanical Efficiency: _____________________________________________________________________________________________________ a comparison of a machine’s work output with the work input. It is expressed as a percentage.

  6. Mechanical efficiency tells you what __________________ of the work input gets converted to work ______________. A machine with 100% mechanical efficiency would be called an _____________ machine and would have _____ friction to overcome. This does not exist! How could you decrease friction in a car engine and improve the mechanical efficiency? _____________________________________________________ percentage output ideal no Lubricate the moving parts with oil. Types of Machines 1. Levers - ______________________________________________________ _____________________________________________ The fixed point is called a _____________________. a simple machine consisting of a bar that pivots at a fixed point that applies a force to a load fulcrum A. First Class Levers – the fulcrum is ________________ the input force and the ______________. They always change the ________________ of the force and the load. between load direction

  7. the load is between the fulcrum and the input force B. Second Class Levers - _____________________________________ ____________________________________ They do NOT change the ________________ of the input force, but they allow you to apply ___________ force over a _______________ distance. direction less greater C. Third Class Levers - ______________________________________ _________________________________________________________ They do NOT change the _______________ of the input force, and they do NOT _________________ the input force. Therefore the _________ force is always less than the ______________ force. The input force is between the fulcrum and the load. direction increase output input

  8. 2. Inclined Planes - _______________________________________________ Ex: ________________ The longer the ________________________ is compared to its ______________, the greater the __________________________________________. The mechanical advantage of an inclined plane is MA = _____________________________ a straight, slanted surface slanted surface a ramp height mechanical advantage length of inclined plane height to which the load is lifted 3. Wedges - _________________________________________________ Ex: ___________________ The greater the distance you move the _________, the greater the force. The mechanical advantage of a wedge is MA = ____________________________ a double inclined plane that moves wedge a knife length of the wedge greatest thickness of the wedge

  9. 4. Screws - _____________________________________________________ When you turn a screw, you exert a ____________ input force over a ________________ turning distance, but the screw itself doesn’t move very far. The longer the _______________ on a screw is, and the closer together the __________________ are, the greater the screw’s __________________ ____________________. an inclined plane that is wrapped in a spiral small large spiral threads mechanical advantage 5. Wheel and Axle - ________________________________________________ _______________________________________ Ex: _____________________ The mechanical advantage of a wheel and axle is MA = ______________________ where the wheel is the larger object and the axle is the smaller object. a simple machine consisting of 2 circular objects of different sizes. doorknob radius of the wheel radius of the axle

  10. a grooved wheel that holds a rope or cable 5. Pulleys - _____________________________________________________ A ________ is attached to one end of the rope and an ____________ force is applied to the other end. load input direction A. Fixed pulleys – These pulleys only change the __________________ of the force. They are attached to something that ___________________. Example: __________________ Since the input and output forces are the same, the mechanical advantage of a fixed pulley is _____. does not move Elevators 1 B. Movable Pulleys – The pulley is attached to the object being moved. It moves up as the load is lifted. It ________________ the force because the input force is exerted over a greater distance than the load is moved. The mechanical advantage is the number of rope segments that support the load. increases

  11. C. Block and Tackle - ___________________________________________ _________________________________________ when a fixed pulley and a movable pulley are used together The mechanical advantage of the block and tackle in the picture is ____ because there are ____ rope segments. 3 3 Machines made up of two or more simple machines 6. Compound Machines - _____________________ __________________________________________ The more moving parts, the _____________ the ________________________________. lower mechanical efficiency A can opener is made up of ____________, ______________, and __________________ __________________. Scissors are a combo of ______________ and _____________. levers 2 levers wedges wedges wheel and axles

  12. Chapter 8 Work and Machines

  13. Work: ___________________________________________________________ ________________________________________________________________ Ex: Pushing a shopping cart Work is ONLY being done when the object moves ____ _____ _________ _____________________ as the force that is acting upon it. In order for work to be done, the object must: 1. _______________ 2. _____________________________________

  14. The mathematical formula for work is W = _____________ where F = _______________ acting upon the object and d = __________________ that the object is moved. The unit used to measure work is _________________ which is equal to a ____________ ___________. Example: A man applies a force of 500 N to push a truck 100 m down the street. How much work does he do? ________________________________________ Example: In which situation do you do more work? A. You lift a 75 N bowling ball 2 m off the floor. B. You lift two 50 N bowling balls 1 m off the floor. Power: ________________________________________________________The mathematical formula for power is P = ______ or power = _________ The unit used to measure power is the ________________ which is equal to _____________________. Example: What is the power of a small motor that can do 4500 J of work in 25 seconds? _________________________________________________

  15. Machines A machine is a device that ________________________________________ ______________________________________________________________ Examples of simple machines are __________________________________ ______________________________________________________________ Input work: _____________________________________________________ ______________________________________________________________ Output work: ____________________________________________________ _______________________________________________________________ **** ________________ can NEVER be greater than ____________________! When the size of the ______________ is changed, the________________ through which the force acts must also change. They are inversely related: when the force _________________, the distance _________________ and when the force _________________, the distance __________________. Using machines does NOT change the amount of work done!!!

  16. Mechanical Advantage: _________________________________________________________________________________________________________ This can be calculated by: MA = ___________________________ Which has a greater mechanical advantage, a machine to which you apply a force of 50 N and the machine applies a force of 150 N, or a machine to which you apply a force of 60 N and the machine applies a force of 200 N? First machine: ________________________________________________ Second machine: _____________________________________________ The larger the _____________ ______________, the easier the machine makes it to do the work. BUT the ___________________ that the output force moves the object ___________________. Work output is always _______ than work input. This is because work must always overcome the force of _________________. Work input is _________ work output plus the work done to overcome the force of friction. Mechanical Efficiency: _____________________________________________________________________________________________________

  17. Mechanical efficiency tells you what __________________ of the work input gets converted to work ______________. A machine with 100% mechanical efficiency would be called an _____________ machine and would have _____ friction to overcome. This does not exist! How could you decrease friction in a car engine and improve the mechanical efficiency? _____________________________________________________ Types of Machines 1. Levers - ______________________________________________________ _____________________________________________ The fixed point is called a _____________________. A. First Class Levers – the fulcrum is ________________ the input force and the ______________. They always change the ________________ of the force and the load.

  18. B. Second Class Levers - _____________________________________ ____________________________________ They do NOT change the ________________ of the input force, but they allow you to apply ___________ force over a _______________ distance. C. Third Class Levers - ______________________________________ _________________________________________________________ They do NOT change the _______________ of the input force, and they do NOT _________________ the input force. Therefore the _________ force is always less than the ______________ force.

  19. 2. Inclined Planes - _______________________________________________ Ex: ________________ The longer the ________________________ is compared to its ______________, the greater the __________________________________________. The mechanical advantage of an inclined plane is MA = _____________________________ 3. Wedges - _________________________________________________ Ex: ___________________ The greater the distance you move the _________, the greater the force. The mechanical advantage of a wedge is MA = ____________________________

  20. 4. Screws - _____________________________________________________ When you turn a screw, you exert a ____________ input force over a ________________ turning distance, but the screw itself doesn’t move very far. The longer the _______________ on a screw is, and the closer together the __________________ are, the greater the screw’s __________________ ____________________. 5. Wheel and Axle - ________________________________________________ _______________________________________ Ex: _____________________ The mechanical advantage of a wheel and axle is MA = ______________________ where the wheel is the larger object and the axle is the smaller object.

  21. 5. Pulleys - _____________________________________________________ A ________ is attached to one end of the rope and an ____________ force is applied to the other end. A. Fixed pulleys – These pulleys only change the __________________ of the force. They are attached to something that ___________________. Example: __________________ Since the input and output forces are the same, the mechanical advantage of a fixed pulley is _____. B. Movable Pulleys – The pulley is attached to the object being moved. It moves up as the load is lifted. It ________________ the force because the input force is exerted over a greater distance than the load is moved. The mechanical advantage is the number of rope segments that support the load.

  22. C. Block and Tackle - ___________________________________________ _________________________________________ The mechanical advantage of the block and tackle in the picture is ____ because there are ____ rope segments. 6. Compound Machines - _____________________ __________________________________________ The more moving parts, the _____________ the ________________________________. A can opener is made up of ____________, ______________, and __________________ __________________. Scissors are a combo of ______________ and _____________.

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