Transcript Slide 1
1 Simple Machines Force 2 Goals Analyze the simple machines qualitatively and quantitatively in terms of force, distance, work and mechanical advantage Be able to calculate mechanical advantage Be able to calculate amount of work done by a simple machine Explain the different types of simple machines. 3 Work Transfer of Energy from one place to another. Applying a force over a certain distance. Calculating Work: Work= Force x distance W = f x d 4 6 types of simple machines Wedge Screw Simple Machines Wheel and Axle Lever Inclined Plane Pulley 5 What is a machine? A device that makes work easier. You still do the same amt of work —it’s just easier! What is a simple machine? -a machine that does work with only one movement. 6 A machine can make work easier in two ways: 1. Multiply the force you apply. A Car Jack 2. Change the direction of the force. Blinds 7 Mechanical Advantage Number of times the machine multiplies the effort force (The force you apply to it) 8 Watch for this in all Simple machines: Machines are a “give and take relationship.” If you get your force multiplied, then you must go a greater distance. 9 Efficiency of a Machine A measure (%) of how much work put into a machine is actually changed to useful work put out by the machine. 90 J . 100 J NEVER OVER 100% 10 Ideal machine According To “The Law of Conservation of Energy” Can this exist? 11 Types of Machines A lever is a bar that is free to pivot, or turn about a fixed point. Levers How can we use levers? 12 Levers Fulcrum Resistance Distance Effort Distance Effort Arm Effort Force LOA D Resistance Arm Resistance Force 13 Levers There are three types of Levers Based on the position of the fulcrum 14 Levers 1st Class: Crowbars, pliers, scissors, seesaw The fulcrum is between the resistance force and the effort force. The closer the fulcrum to the resistance force, the more the lever multiplies the force. 15 Levers •Wheelbarrow •Nutcrackers •Crowbar (forcing two objects apart) •The handle of a pair of nail clippers 2nd Class: The resistance force is between the effort force and the fulcrum. 16 Levers 3rd Class: the effort force is between the resistance force and the fulcrum. •Hoe •Your arm •Catapult • Fishing rod •Tongs (double lever) (where hinged at one end) Mechanical Advantage of Levers 17 5/5=1 Effort arm Resistance arm 10/5=2 20/5=4 As the length of the effort arm increases, the MA of the lever increases. 18 REVIEW Position of Fulcrum 19 Pulleys 20 Pulleys • What is a pulley? • A pulley is a grooved wheel with a rope or chain running along the groove. • What can a pulley be used for? 1.Multiply the effort force 2.change the direction of the force Pulleys 21 Two types of Pulleys: 1. Fixed pulley – – A pulley that is attached to something Only changes the direction of the force – The pulley is free to move 2. Movable pulley ***Block and Tackle*** Combination of both types of pulleys Mechanical Advantage of Pulleys 22 10 N resistance Force Effort Force 10 N Mechanical Advantage of Pulleys 23 Mechanical Advantage of Pulleys 24 Mechanical Advantage of Pulleys 25 26 27 28 Inclined Plane A sloping surface that that reduces the amount of force required to raise and object. Resistance Distance (h) Effort Distance (l) Mechanical Advantage of Inclined Planes 29 Resistance Distance (h) Effort Distance (l) Mechanical Advantage of Inclined Planes 30 31 Wheel and Axle • Consisting of two wheels of different sizes that rotate together • The effort force is applied to the larger wheel Ideal Mechanical Advantage = Radius of wheel Of wheel and axel Radius of axel Gears are wheels with teeth. 32 Screw • An inclined plane wrapped around a cylinder • The inclined plane lets the screw slide into the wood. Examples: Bolt, Spiral Staircase 33 34 Wedge • An inclined plane with one or two sloping sides. • Changes the direction of the Examples: Axe, Zipper, Knife effort force. Effort Force Resistance force 35 36 Rube Goldburg 37 CLIP 38 A lever is used to lift a box. The mechanical advantage of the lever is 39 A 25 B 10 C5 D4 It took only 200 N of force to lift a 1000N 50 cm object, therefore the machine multiplied 10 cm the force 5 times! OR 40 What is the amount of useful work output of a 25% efficient bicycle if the amount of work input is 88 Nm? A 2200 N-m B 113 N-m C 63 N-m D 22 N-m .25 = Wout 88 J 41 Which of the following is an example of a compound machine? A bicycle B crowbar C doorknob D ramp