Chapter 15 Machines

15-1 What is a simple machine? People use machines to make work easier They allow a person to -change the size of the force -change the direction of the force -change speed of the force Effort Force-the force you apply to a machine Resistance Force-the force that opposes the effort force

15-1 (Continued) Mechanical Advantage-the number of times a machine multiplies the effort force (has no label, just written as a number) Mechanical advantage (MA) is always less due to friction… Ideal Mechanical Advantage (IMA) is without friction. Formula: MA = resistance force  effort force

Six Simple Machines Pulley Lever Inclined Plane Wheel and Axle Screw Wedge

15-2 What is Efficiency Efficiency-the ratio of work output to work input. It is usually expressed as a percent. Formula: Efficiency = work output  work input x 100 * The efficiency of a machine is always less than 100% because of friction. Work output - work done by a machine Work input – work done on a machine

15-3 How does a lever work? A lever is a bar that moves on a fixed point Fulcrum-fixed point that a lever pivots on. IMA = Effort Arm Length IMA = Effort Arm Length Resistance Arm Length Resistance Arm Length Three different classes of levers; 1 st Class2 nd Class3 rd Class

1 st Class Lever Examples: crow bar, see saw, paint can opener

2 nd Class Lever Examples; nut cracker, wheel barrow

3 rd Class Lever Examples; fishing pole, broom,

Mechanical Advantage of a Lever Problem What would be the Mechanical Advantage (M.A.) of a Lever with an effort arm length of 2 meters and a resistance arm of.5 meters? What would be the Mechanical Advantage (M.A.) of a Lever with an effort arm length of 2 meters and a resistance arm of.5 meters? Answer

IMA = Effort Arm Length Resistance Arm Length IMA = Effort Arm Length Resistance Arm Length IMA = 2 m.5 m.5 m IMA = 4 (remember no label for M.A.)

15-4 How do Pulleys Work? Pulley-rope, belt or chain wrapped around a grooved wheel. A pulley can be used to change the direction of the force and/or increase the amount of force. Pulleys can be fixed or moveable. To calculate the IMA of a Pulley System…… -Count the number of rope segments on each side of the pulleys, including the free end. -This is the IMA, unless the free end is pulled down you need to subtract one.

Pulley (continued)

Block and Tackle - a pulley system consisting of both fixed and moveable pulleys

15-5 What are Inclined Planes? Inclined Plane- slanted surface or ramp that makes work easier. MA = length  height Example: What would be the mechanical advantage (M.A.) of an inclined plane with a height of 200 cm and a length of 1200 cm? Answer

M.A. = length M.A. = length height height M.A. = 1200 cm M.A. = 1200 cm 200 cm 200 cm M.A.=6 M.A.=6 (remember there is no label for M.A.)

15-5 (Continued) Screw-inclined plane wrapped around a cylinder. Examples; car jack, corkscrew

15-5 (continued) Wedge is two inclined planes placed back to back. Examples; Tip of screwdriver, chisel, axe, knife

Wheel and Axle Wheel and Axle -made up of two circular objects of different size. The axle is attached to the center of the larger wheel radius-distance from the center to the edge of a circle. (This is equal to half of the diameter. I.M.A. can be calculated: I.M.A.= radius of the wheel radius of the axle radius of the axle

Wheel and Axle Problem What would be the Mechanical Advantage of a wheel and axle if the wheel has a diameter of 40 cm and the axle has a diameter of 10? Answer

I.M.A.= radius of the wheel radius of the axle First, you must divide the diameter by 2 in order to determine the radius! Radius of wheel= 20 cm Radius of axle = 5 cm I.M.A.= 20 cm 5 cm I.M.A.= 4 (remember M.A. has no label)