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Machines usage, Input/OutPut , and efficiency

Machines usage, Input/OutPut , and efficiency. Work and Machines. Machines make work easier to do. They change the size of a force needed, the direction of a force, or the distance over which a force acts. How?. Increase force

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Machines usage, Input/OutPut , and efficiency

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  1. Machines usage, Input/OutPut, and efficiency

  2. Work and Machines • Machines make work easier to do. • They change the size of a force needed, the direction of a force, or the distance over which a force acts.

  3. How? • Increase force • Each complete rotation of the jack handle applies a small force over a large distance. However, each rotation lifts the car only a very short distance. Thus a small force exerted over a large distance becomes a large force exerted over a short distance. • BUT if a machine increases the distance over which you exert a force, then it decreases the amount of force you need to exert.

  4. Increase Direction • Some machines decrease the applied force, but increase the distance over which the force is exerted. The arrows show how pulling the end of each oar through a small distance moves the end of the oar in the water through a large distance. • BUT the increased travel of the oar through the water requires you to exert a greater force. A machine that decreases the distance through which you exert a force increases the amount of force required.

  5. Changing Direction • Some machines change the direction of the applied force. Pulling back on the handle of the oar causes its other end to move in the opposite direction. So not only can machines change the amount of force and the distance the force acts through, but they can also change the direction of the force.

  6. Input • Force Input- force you exert on a machine • Input distance-distance the input force acts through. • Work Input- work done by the input force acting through the input distance. • Work input equals the input force multiplied by the input distance.

  7. Output • Output force is the force exerted by a machine. • The distance the output force is exerted through is the output distance. • Work output of a machine is the output force multiplied by the output distance.

  8. Look at the output force, distance, and work for the oars. How are the input work and output work related? Although nearly equal, the output work is less than the input work because of friction. All machines use some amount of input work to overcome friction.

  9. Can you increase the work output of the oar by positioning it differently? • Unless the new position decreases friction, the answer is no. If there is no change in the work input, there cannot be an increase in the work output. The only way to increase the work output is to increase the amount of work you put into the machine. You cannot get more work out of a machine than you put into it!

  10. Mechanical Advantage • The mechanical advantage of a machine is the number of times that the machine increases an input force. • Suppose a nut is in the nutcracker at position A. In this position, the nutcracker exerts a force on the nut about seven times greater than the force you exert on the nutcracker. In position A the nutcracker's mechanical advantage is about 7. However, if the nut is moved to position B, the mechanical advantage decreases to about 3. A B

  11. The mechanical advantage determined by measuring the actual forces acting on a machine is the actual mechanical advantage. The actual mechanical advantage (AMA) equals the ratio of the output force to the input force.

  12. The ideal mechanical advantage (IMA) of a machine is the mechanical advantage in the absence of friction.   Because friction is always present, the actual mechanical advantage of a machine is always less than the ideal mechanical advantage.

  13. Examples A student working in a grocery store after school pushes several grocery carts together along a ramp. The ramp is 3 meters long and rises 0.5 meter. What is the ideal mechanical advantage of the ramp? IMA= 3m/0.5m= 6

  14. A construction worker moves a crowbar through a distance of 0.50 m to lift a load 0.05 m off of the ground. What is the IMA of the crowbar? IMA= .5m/.05m= 10

  15. Efficiency • The percentage of the work input that becomes work output is the efficiency of a machine. • Because there is always some friction, the efficiency of any machine is always less than 100 percent.

  16. Efficiency is usually expressed as a percentage. For example, if the efficiency of a machine is 75 percent, then you know that 75 percent of the work input becomes work output. If a machine requires 10.0 J of work input to operate, then the work output is 75% of 10.0 J.

  17. Formulas Work Input=

  18. Examples You have just designed a machine that uses 1000 J of work from a motor for every 800 J of useful work the machine supplies. What is the efficiency of your machine? 800J/1000J x 100% 80%

  19. If a machine has an efficiency of 40%, and you do 1000 J of work on the machine, what will be the work output of the machine? 1000J x 40/ 100 400J

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