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## Chapter 9 - Simple Machines

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### Simple machines are all about using mechanical advantage to make what ordinarily ... The gear ratio is the ... A ramp is a simple machine that allows you to raise a ... – PowerPoint PPT presentation

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Title: Chapter 9 - Simple Machines

1
Chapter 9 - Simple Machines
• pp. 210-216

2
• Mechanical advantage is the ratio of output force
to input force.

3
• Machines multiply forces.
• One person could lift an elephantquite a heavy
loadwith a properly designed system of ropes and
pulleys!

4
9.2 Simple Machines and Mechanical Advantage
• Simple machines are all about using mechanical
advantage to make what ordinarily would be a

5
Output force (N)
MA Fo Fi
Input force (N)
6
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7
9.2 The Lever
• A lever includes a stiff structure (the lever)
that rotates around a fixed point called the
fulcrum.

8
9.2 The Lever
• Levers are useful because you can arrange the
fulcrum and the input arm and output arm to

9
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10
9.2 The Lever
• Each class of levers is defined by the location
of the input and output forces relative to the
fulcrum.

11
9.2 Gears
• Many machines require that rotating motion be
transmitted from one place to another.
• Gears change force and speed.

12
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.

13
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 output gear
14
9.2 Tension
• Ropes and strings carry tension forces along
their length.
• If the rope is not moving, its tension is equal
to the force pulling on each end.

15
9.2 Ramps
• A ramp 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.

16
9.2 Screws
• A screw is a rotating ramp.
• You find the mechanical advantage of a screw by
dividing its circumference by the lead.

17
9.2 Wedge
• A wedge 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 inversely
related to the size of the wedge angle.

18
9.2 Wheel and axle
• A wheel rotates around a rod called an axle.
• The mechanical advantage is the ratio of the
• The wheel and axle move together to move or lift

19
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

20
Solving Problems
• Looking for