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Machines - Ch. 7 II. The Simple Machines (p.180-183) Lever Pulley Wheel & Axle Inclined Plane Screw Wedge.

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Presentation on theme: "Machines - Ch. 7 II. The Simple Machines (p.180-183) Lever Pulley Wheel & Axle Inclined Plane Screw Wedge."— Presentation transcript:

1 Machines - Ch. 7 II. The Simple Machines (p.180-183) Lever Pulley Wheel & Axle Inclined Plane Screw Wedge

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

3 A. 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.

4 A. Lever First Class Lever can increase force, distance, or neither changes direction of force

5 A. Lever Second Class Lever always increases force

6 A. Lever Third Class Levers always increases distance

7 B. Pulley Pulley grooved wheel with a rope or chain running along the groove a flexible first-class lever LeLe LrLr F

8 B. Pulley Ideal Mechanical Advantage (IMA) equal to the number of supporting ropes IMA = 0IMA = 1IMA = 2

9 B. Pulley Fixed Pulley IMA = 1 does not increase force changes direction of force

10 B. Pulley Movable Pulley IMA = 2 increases force doesnt change direction

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

12 C. Wheel and Axle Wheel and Axle two wheels of different sizes that rotate together a pair of rotating levers Wheel Axle

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

14 Problems You use a 160 cm plank to lift a large rock. If the rock is 20 cm from the fulcrum, what is the planks 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

15 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

16 Problems A steering wheel requires a mechanical advantage of 6. What radius does the wheel need to have if the steering column has a radius of 4 cm? GIVEN: IMA = 6 r e = ? r r = 4 cm WORK : r e = IMA · r r r e = (6)(4 cm) r e = 24 cm IMA rere r r rere

17 Problems You need to lift a 150 N box using only 15 N of force. How long does the lever need to be if the resistance arm is 0.3m? GIVEN: F r = 150 N F e = 15 N L r = 0.3 m L e = ? MA = 10 WORK : L e = IMA · L r L e = (10)(0.3) L e = 3 m Total length = L e + L r Total length = 3.3 m IMA LeLe LrLr 0.3m ? 150N 15N


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