U3d-L8 2 nd Semester Participation Policy 31 JAN 2011 Participation is 15% of quarter grade Lose points for –Coming to class late –Talking without raising your hand –Not attempting your drills –Getting out of your seat without raising your hand Gain points by positively participating in class

1.Review Levers 2.To understand and calculate Mechanical Advantage (MA) for various simple mechanisms 3.To know and apply the three simple mechanisms based on the inclined plane TODAY’S OBJECTIVES U3d-L8

Machines are… –artifacts that transmit or change the application of power, force, or motion. What is an artifact? –something created by humans usually for a practical purpose. Machines can be simple or complex –Complex machines are comprised of…. Simple Machines U3d-L8

U3d-L1 F x d = W Wo / Wi = Eff TWO IMPORTANT EQUATIONS

1. A hot air balloon carries 200 lbs cargo, 150 lbs human, and 200 lbs materials up a distance of 2,000 feet. How much work did the balloon do (keep all units)? U3d-L3 2.A physical therapy doctor told his 150-lb patient to do 30,000 ft-lbs of work each day to rehabilitate his leg. The patient decides to climb a hill to perform this work. How high does the patient need to climb in order to meet his goal? 1. F x d = W 550 lbs x 2,000 ft = W = 1,100,000 ft-lbs. 2. F x d = W 150 lbs x d = 30,000 ft-lbs. 150 lbs. d = 200 ft.

U3d-L5 Which class is the lever below? Describe it. FIRST CLASS SECOND CLASS THIRD CLASS

U3d-L4 3 Categories of simple machines based on the principle of the LEVER: LEVER LeverWheel and AxlePulley

Sketch the pictures below and answer the questions: Which lever would be easier to push down, A or B? Which load will travel the greater distance, A or B? U3d-L5 AB

MECHANICAL ADVANTAGE FORCE MULTIPLIERS F L DLDF For All Lever Classes What are the units for MA?There are no units – it’s a ratio DF DL M.A.= LFLF = MA is the number of times a mechanical device multiplies the Applied Force U3d-L8

You now have 2 equations: L x DL = F x DF DFL DLF FORCE MULTIPLIERS = Hint: They’re really the same equation rearranged

1.A 1st-class lever is used to lift a bureau that weighs 80 lbs. The bureau is located 3 feet from the fulcrum. A child who applies the force to the other side of the lever has only 20 lbs. of strength to push. How far from the fulcrum should the child apply the force? (HINT: Sketch a picture, list the given information, write your equation, and solve for the unknown) 80 lbs. 3 ft.DF = ? F = 20 lbs. L = 80 lbs. DF = ? DL = 3 ft. F = 20 U3d-L8

80 lbs. 3 ft.DF = ? F = 20 lbs. L = 80 lbs. DF = ? DL = 3 ft. F = 20 L x DL = F x DF 80 lbs x 3 ft = 20 lbs x DF 240 ft-lbs = 20 lbs x DF 20 ft 20 ft DF = 12 ft U3d-L8

80 lbs. 3 ft.DF = ? F = 20 lbs. L = 80 lbs. DF = ? DL = 3 ft. F = 20 DF = 12 ft What is the Mechanical Advantage of this lever? DF DL M.A.= 12 ft. 3 ft. = 4 = U3d-L8

80 lbs. 3 ft.DF = ? F = 20 lbs. L = 80 lbs. DF = ? DL = 3 ft. F = 20 lbs. DF = 12 ft MA = 4 What does F x MA = ? L U3d-L8

80 lbs. 3 ft.DF = ? F = 20 lbs. L = 60 lbs. DF = 4 ft. DL = 2 ft. F = 30 lbs. What is the Mechanical Advantage of this lever? DF DL M.A.= 4 ft. 2 ft. = 2 = U3d-L8

20 lbs. 3 ft. DL = ? F = 80 lbs. L = 20 lbs. DF = ? DF = 3 ft. F = 80 DL = 12 ft What is the Mechanical Advantage of this lever? DF DL M.A.= 3 ft. 12 ft. = 1/4 = U3d-L8

L DF DL F What class of lever is this? What is the maximum efficiency?

U3d-L5 Which class of lever? WHEEL-and-AXLE 2 nd Class

U3d-L5 Which class of lever? WHEEL-and-AXLE 3 rd Class

M.A. = Radius (D) to Force (F) = DF Radius (D) to Load (L) DL Rotary Motion the circular motion which occurs when the wheel and axle are rotated about the centerline axis. Linear Motion the straight-line motion which occurs when a wheel rolls along a flat surface. The linear distance traveled when the wheel completes one revolution is equal to the circumference of the wheel. Circumference = Pi * Wheel diameter U3d-L8 WHEEL AND AXLE

U3d-L8 DRILL – What is the mechanical advantage for each system FEBRUARY 1, lbs. F = 20 lbs. DF = 15 ftDL = 3 ft DF = 10 in DL = 2 in

U3d-L8 80 lbs. F = 20 lbs. LFLF M.A.= 80 lb 20 lb 4= =

U3d-L8 DF M.A.= 15 ft 3 ft 5= = DF = 15 ftDL = 3 ft

U3d-L8 DF = 10 in DL = 2 in M.A. = Radius (D) to Force (F) = DF = 10 in Radius (D) to Load (L) DL 2 in 5=

A pulley is an adaptation of a wheel and axle. A single pulley simply reverses the direction of a force. When two or more pulleys are connected together, they permit a heavy load to be lifted with less force. The trade-off is that the end of the rope must move a greater distance than the load. U3d-L8 PULLEY

U3d-L8 M.A. = Total number of strands supporting the load MA = L / F PULLEY

Fixed Pulley – when a pulley is attached or fixed to a strong member, which will not move. How many strands are supporting the load? What is the MA of a fixed pulley? How many lbs of force are required to lift 100 lbs of load? When a fixed pulley is used, the force needed to lift a weight does not change. U3d-L PULLEY

Movable Pulley – splits the work in half. How many strands are supporting the load? What is the MA of a movable pulley? How many lbs of force are required to lift 100 lbs of load? When a movable pulley is used, the force needed to lift a load is half that of the load. U3d-L PULLEY

Block and Tackle – a system of three pulleys How many strands are supporting the load? What is the MA of a movable pulley? How many lbs of force are required to lift 120 lbs of load? When a block and tackle is used, the force needed to lift a load is 1/3 that of the load. U3d-L PULLEY

How much force is needed to lift the load for each system U3d-L8 Drill L = 60 lb Block and Tackle, M.A.=3 F = 20 lb Movable Pulley, M.A.=2 F = 30 lb Fixed Pulley, M.A.=1 F = 60 lb F F F

3 Categories of simple machines based on the principle of the INCLINED PLANE: INCLINED PLANE Inclined PlaneWedgeScrew U3d-L8

Inclined Plane – sloped surfaces used to make a job easier –Easier to go up a slope than a vertical surface Wedge – used to split, separate, and grip –Wood chisel, firewood axe, doorstop Screw – an inclined plane wrapped around a shaft –1/2-inch x 12 machine screw ½” diameter 12 threads per inch U3d-L8

The inclined plane is the simplest machine of all the machines. An inclined plane is a flat sloping surface along which an object can be pushed or pulled. An incline plane is used to move an object upward to a higher position. H D L F M.A.= Distance = D Height H

U3d-L8 FORCE 1.During its use, an inclined plane remains stationary, while the wedge moves. 2.With an inclined plane the effort force is applied parallel to the slope of the incline. 3.With a wedge the effort force is applied to the vertical edge (height) incline.

U3d-L8 DHDH M.A.= FORCE D D H H

U3d-L8 What is the Mechanical Advantage for these two inclined planes 3ft 4 ft 5 ft 3ft 4 ft 5 ft DHDH M.A.= = 5/3 DHDH M.A.= = 5/4

U3d-L8 Mechanical Advantage for Levers, Wheel and Axle, Pulleys, and Incline Planes MachineMechanical Advantage LeverL/F = DF/DL Wheel and AxleDF/DL PulleyL/F = Number of Strands supporting load Incline PlaneD/H For classwork complete both sides of handout