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Simple Machines Chapter 7-Part 2

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Pulleys Pulley A grooved wheel with a rope or a chain running along the groove.

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Positioning Pulleys Remember: MA (IMA) < 1 means the machine does not make work easier. MA = 1 does not make work easier. MA> 1 makes work easier Fixed pulley Attached to something that doesn’t move IMA = 1 so it does not multiply the effort force Movable pulley Not attached to a fixed point Multiplies the effort force IMA > 1 Block and tackle Fixed and movable pulleys combined to increase the mechanical advantage IMA > 1

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Wheel and Axle –A simple machine consisting of two wheels of different sizes that rotate together. Examples: doorknobs, faucets, ice cream makers IMA = radius of wheel = R w radius of axle R a Example: In an ice-cream freezer the wheel has a radius of 20 cm. The axle has a radius of 15 cm. What is the ideal mechanical advantage of the wheel and axle? Answer: 1.34

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Inclined plane –A ramp which is a sloping surface used to raise objects. »IMA = Effort distance = length of slope = _l_ Resistance distance height of slope h The Pyramids Scientists disagree whether the pyramids were built using inclined planes or levers. They were most likely made using both of these simple machines.

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Screw –An inclined plane wrapped in a spiral around a cylindrical post. Wedge –An inclined plane with one or two sloping sides »Chisels, knives and axe blades

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Compound Machines A combination of two or more machines. –Examples: lawn mower, bicycle, axe

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Gears –Gears are modified wheels and axles. A wheel with teeth along its axles. –Effort exerted on one of the gears causes the other gear to move.

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Efficiency A measure of how much of the work put into a machine is changed to useful work put out by a machine. Efficiency = W out x 100% = F r x d r x 100% W in F e x d e Power is the rate at which work is done. If two people were pushing boxes of the same weight the same distance the one who finished it first would have exerted the most power. The amount of work is the same, the only difference is the speed at which the work is done. Power = work P = W time T

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Homework Day 1: Read pp Day 2: Vocab. #5-8, 10. Day 3: Check.Conc: #5-7, 9. Day 4: Think. Crit. # 16 and 20 Day 5: Finish Lab #10 (as much as we covered in class) Take CH. 7 test. Due Date: EIE: Dec. 11 th.

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Study Sheet for CH. 7 test What is a simple machine? Know what 1 st, 2 nd and third class levers are and examples of each. Calculations for IMA and MA MA= resistance force = F r effort force F e IMA – length of effort arm = L e length of resistance are L r Or for inclined plane: length of slope height of slope A screw and a wedge are examples of what? Go over the vocabulary words given at the end of the chapter. Go over the checking concepts questions. Go over all the Thinking critically questions assigned in the last 2 weeks.

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