Work & Machines

Work  Work transfer of energy through motion force exerted through a __________ W = Fd Distance must be in direction of ______! W:work (___) F:force (____) d:distance (__) 1 J = 1 N·m F W d

Try these!!!  A mover lifts a 98 N box 1.8 m from the ground to a shelf. How much work is done on the box?  Alice has a heavy pocketbook. Each morning to lifts it off the ground and puts it on the counter that is 1.6 m from the floor. In doing this she does 8 J of work. How much does the pocketbook weigh?

Practice  Pick up a Work worksheet from the front table & complete #1-10

Do you want to do all the work yourself?  Of course not!  What do we use that helps us do work?  MACHINES !!!

MachinesMachines II. The Simple Machines  Lever  Pulley  Wheel & Axle  Inclined Plane  Screw  Wedge

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A. Lever  Lever a bar that is free to pivot about a fixed point, or ____________ “Give me a place to stand and I will move the Earth.” – Archimedes Engraving from Mechanics Magazine, London, 1824 Effort arm Resistance arm ________

Lever  Ideal Mechanical Advantage (IMA) frictionless machine Effort arm length Resistance arm length L e must be greater than L r in order to multiply the force.

Lever  First Class Lever can increase force, distance, or neither changes direction of force

Lever  Second Class Lever always increases __________.

Lever  Third Class Levers always increases __________.

Pulley  Pulley grooved wheel with a ______ or chain running along the groove a “flexible first-class lever” LeLe LrLr F

Pulley  Ideal Mechanical Advantage (IMA) equal to the number of supporting ____________ IMA = 0IMA = 1IMA = 2

Pulley  Fixed Pulley IMA = ____ does not increase force changes direction of force

Pulley  Movable Pulley IMA = ____ increases force doesn’t change direction

B. Pulley  Block & Tackle combination of fixed & movable pulleys increases force (IMA = 4) may or may not change ___________

Wheel and Axle  Wheel and Axle two wheels of _________sizes that rotate together a pair of “rotating levers” Wheel Axle

Wheel and Axle  Ideal Mechanical Advantage (IMA) effort force is usu. applied to wheel axle moves less _________ but with greater force effort radius resistance radius

Problems  You use a 160 cm plank to lift a large rock. If the rock is 20 cm from the fulcrum, what is the plank’s IMA? GIVEN: L r = 20 cm L e = 140 cm IMA = ? WORK : IMA = L e ÷ L r IMA = (140 cm) ÷ (20 cm) IMA = 7 IMA LeLe LrLr 20cm 160cm

Problems  A crank on a pasta maker has a radius of 20 cm. The turning shaft has a radius of 5 cm. What is the IMA of this wheel and axle? GIVEN: r e = 20 cm r r = 5 cm IMA = ? WORK : IMA = r e ÷ r r IMA = (20 cm) ÷ (5 cm) IMA = 4 IMA rere r 5 cm 20 cm