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##### Chapter Nine: Simple Machines

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**Chapter Nine: Simple Machines**• 9.1 Types of Simple Machines • 9.2 Mechanical Advantage • 9.3 Levers in the Human Body**9.2 The Lever**• A _______ includes a stiff structure (the lever) that rotates around a fixed point called the __________.**9.2 The Lever**• Levers are useful because you can arrange the fulcrum and the input arm and output arm to adjust the mechanical advantage of the lever.**9.2 The Lever**• Each class of levers is defined by the location of the input and output forces relative to the fulcrum.**9.2 Gears**• Many machines require that rotating motion be transmitted from one place to another. • Gears change ________ and _________**9.2 Designing Gear Machines**• The gear ratio is the ratio of output turns to input turns. • You can predict how force and speed are affected when gears turn by knowing the number of teeth for each gear.**9.2 Gear Ratios**Number of teeth on input gear To=Ni Ti No Turns of output gear Turns of input gear Number of teeth on input gear**9.2 Tension**• Ropes and strings carry ________forces along their length. • If the rope is not moving, its tension is equal to the force pulling on each end.**9.2 Ramps**• A _________ is a simple machine that allows you to raise a heavy object with less force than you would need to lift it straight up. • The mechanical advantage of a ramp is the ramp length divided by the height of the ramp.**9.2 Screws**• A ________is a rotating ramp. • You find the mechanical advantage of a screw by dividing its circumference by the _______.**9.2 Screws**• A ________ is like a ramp that can work while in motion (a ramp is always stationary). • A wedge has a side that slopes down to a thin edge. • The mechanical advantage for a wedge is __________ related to the size of the wedge angle.**9.2 Wheel and axle**• A _______ rotates around a rod called an _______ • The mechanical advantage is the ratio of the radius of the wheel to the radius of the axle. • The wheel and axle move together to move or lift loads.**Solving Problems**• A crowbar is a type of lever that you use to pull a nail out of a piece of wood. • If the handle of a crowbar is 40 centimeters and the foot is 2 centimeters, what is its mechanical advantage?**Solving Problems**• Looking for: • …mechanical advantage of lever • Given • …input arm = 40 cm; output arm = 2 cm • Relationships: • M.A. = Length of input arm Length of output arm • Solution • M.A. = 40 cm ÷ 2 cm = 20