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Machines

Machines. Ch. 5 Sect. 2. A machine is a device that makes doing work easier Three ways that machines make work easier: 1. Increase the force that can be applied to an object i.e. Screwdriver turning a screw, using a crowbar to pry something open

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Machines

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  1. Machines Ch. 5 Sect. 2

  2. A machine is a device that makes doing work easier • Three ways that machines make work easier: 1. Increase the force that can be applied to an object • i.e. Screwdriver turning a screw, using a crowbar to pry something open 2. Increase the distance over which a force can be applied • If work stays the same and distance increases, the required force will be decreased • i.e. Pushing an object up a ramp 3. Change the direction of the applied force. • i.e. Using a car jack, chopping wood with an axe, opening/closing blinds Machines

  3. A machine that does work with only one movement of the machine Types • Lever • Pulley • Wedge • Inclined Plane • Screw • Wheel & Axle Simple Machines • With a simple machine you can never increase both the force and the distance! If you gain one, you sacrifice (lose) the other.

  4. There are two forcesinvolved when a machine is used for work: 1. Input force (Finput)– the force that is applied to the machine 2. Output force (Foutput)– the force that is applied by the machine Machines

  5. There are two kinds of workthat need to be considered 1. Input work (Winput)- The work done by you on the machine 2. Output work (Woutput)- The work done by the machine • Remember that energy is conserved. • When you do work you transfer energy to the machine. • When the machine does work on an object, energy is transferred to the object. • Because energy cannot be created or destroyed, the amount of energy transferred to the object cannot be greater than the amount of energy you transferred to the machine. • Woutputis never greater than Winput. Machines

  6. Ideal Machine • A perfect machine in which there was no friction. • No work would be “lost” to heat. • For an ideal machine, Winput = Woutput. Real Machine • For real machines, some of the energy put into a machine is always converted into heatby frictional forces. • Therefore, Woutput < Winput. Ideal vs. Real Machines

  7. Efficiency is a measure of how much of the work put into a machine is changedinto useful output workby the machine. • A high efficiency machine produces lessheatfrom friction so more of the input work is changed to useful output work. • Efficiency can be calculated by: Efficiency

  8. In an ideal machine there is no friction and the output work equalsthe input work. So the efficiency of an ideal machine is 100%. • In a real machine, friction causes the output work to always be less than the input work. So the efficiency of a real machine is always less than 100%. Efficiency

  9. Machines can be made more efficient by reducing friction. • This is usually done by adding a lubricant, such as oil or grease, to surfaces that rub together. • A lubricant fills in the gaps between the surfaces, enabling the surfaces to slide past each other more easily. Efficiency

  10. An inclined plane allows you to do 280 J of useful work on a refrigerator that you are sliding upward along the plane. If the work that you have to do is 760 J, what is the efficiency of the inclined plane? • A lever requires you to push with 75N of force to move it 1 meter. The 125 N rock on the other end moved 0.3 m. What is the efficiency of this lever? Win = 760 J Wout = 280 J Calculating Efficiency Win = 75 N x 1 m = 75 J Wout = 125 N x 0.3 m = 37.5 J

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