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Simple Machines

Simple Machines. Chapter 14. What do All These Things Have in Common?. Questions. What is the function of the machines? How many moving parts do they have? How do the parts work together? How does this machine make work easier?. Machines change the Way Force is Applied.

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Simple Machines

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  1. Simple Machines Chapter 14

  2. What do All These Things Have in Common?

  3. Questions • What is the function of the machines? • How many moving parts do they have? • How do the parts work together? • How does this machine make work easier?

  4. Machines change the Way Force is Applied • A machine is any device that helps people do work. • They change the way in which work is done.

  5. How Could we Move this Couch Easier?

  6. Machines • If machines do not reduce the amount of work required, how do they help people do work? Machines make work easier by changing • The size of the force needed to do the work and the distance over which the force is applied. • The direction in which the force is exerted.

  7. Have you ever tried to open a door by turning the doorknob’s shaft instead of the handle? The doorknob allows you to use less force to turn the handle instead of the shaft.

  8. Machines: Changing Size & Direction • The doorknob is a machine. It allows you to apply a smaller force over a greater distance. • The boy using the rake is a machine. He moves his hands a short distance to move the end of the rake a large distance, Allowing him to rake more Leaves.

  9. Machines • Input Force is the force exerted on a machine. • Output Force is the force that a machine exerts on an object. • Picture on page 450

  10. Changing Direction • Machines also help you work by changing the direction of force. • You pull down on a rope and the flag moves up.

  11. Mechanical Advantage • When machines help you work, there is an advantage—or benefit– to using them? Mechanical = Output Force Advantage Input Force

  12. Mechanical Advantage • For machines that allow you to apply less force over a greater distance– such as a doorknob– the output force is greater than the input force. • Therefore, the mechanical advantage of this type of machine is greater than 1. • For example, if the input force is 10 newtons and the output force is 40 newtons, the mechanical advantage is: • 40 N / 10 N • MA= 4

  13. Mechanical Advantage • Sometimes changing the direction of the force is more useful than decreasing the force or distance. • Therefore, the mechanical advantage of the machine is 1.

  14. Practice Problem • The output force of a machine is 600 N and the input force is 200 N. What is the mechanical advantage of the machine? MA= Output force = 600 N = 3 Input Force 200 N

  15. Work Transfers Energy • Machines transfer energy to objects on which they do work!

  16. Energy • When you lift an object, you transfer energy to it in the form of gravitational potential energy– that is, potential energy caused by gravity

  17. Work • When you use a machine to do work, there is always an exchange, tradeoff, between the force you use to do the work and the distance over which you apply that force.

  18. Mountain ClimbingPage 453 • Short Route: Climbing straight up covers a shorter distance but more force must be applied against gravity • Long Route: Climbing a gentle slope, the climber covers more distance but uses less force.

  19. Efficiency • The work you put into a machine will always be greater than the work done by the machine. Some input work is always lost in overcoming friction. Efficiency (%) = Output work x 100 Input work

  20. Efficiency and Energy • Work transfers energy and that machines make work easier. • Work transfers energy and that machines make work easier.

  21. Energy Efficiency • Many appliances come with energy guides that can help a buyer compare the energy efficiency of different models. • A washing machine with the highest energy rating may not always save the most energy, because users may have to run those machines more often.

  22. Review Questions • In what ways can a machine change a force? • By changing the size of a force, changing its direction, or both • How is a machine’s efficiency calculated? Efficiency (%) = Output work x 100 Input work

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