2 PulleysPulleyA grooved wheel with a rope or a chain running along the groove.
3 Positioning Pulleys Fixed pulley Movable pulley Block and tackle Remember: MA (IMA) < 1 means themachine does not make work easier.MA = 1 does not make work easier.MA> 1 makes work easierFixed pulleyAttached to something that doesn’t moveIMA = 1 so it does not multiply the effort forceMovable pulleyNot attached to a fixed pointMultiplies the effort forceIMA > 1Block and tackleFixed and movable pulleys combinedto increase the mechanical advantage
4 Wheel and AxleA simple machine consisting of two wheels of different sizes that rotate together.Examples: doorknobs, faucets, ice cream makersIMA = radius of wheel = Rwradius of axle RaExample: 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
5 Inclined planeA ramp which is a sloping surface used to raise objects.IMA = Effort distance = length of slope = _l_Resistance distance height of slope hThe PyramidsScientists disagree whether the pyramids were built using inclined planes or levers. They were most likely made using both of these simple machines.
6 ScrewAn inclined plane wrapped in a spiral around a cylindrical post.WedgeAn inclined plane with one or two sloping sidesChisels, knives and axe blades
7 Compound Machines A combination of two or more machines. Examples: lawn mower, bicycle, axe
8 GearsGears are modified wheels and axles. A wheel with teeth along its axles.Effort exerted on one of the gearscauses the other gear to move.
9 EfficiencyA measure of how much of the work put into a machine is changed to useful work put out by a machine.Efficiency = Wout x 100% = Fr x dr x 100%Win Fe x dePower 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 = Wtime T
10 Homework Day 1: Read pp. 190-203 Day 2: Vocab. #5-8, 10. Day 3: Check.Conc: #5-7, 9.Day 4: Think. Crit. # 16 and 20Day 5: Finish Lab #10 (as much as we covered in class)Take CH. 7 test.Due Date: EIE: Dec. 11th.
11 Study Sheet for CH. 7 test What is a simple machine? Know what 1st, 2nd and third class levers are and examples of each.Calculations for IMA and MAMA= resistance force = Freffort force FeIMA – length of effort arm = Lelength of resistance are LrOr for inclined plane: length of slopeheight of slopeA 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.