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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
  • 9.2 Mechanical Advantage
  • pp. 210-216

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

3
9.2 Mechanical advantage
  • 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
    complex task into a much simpler task.

5
9.1 Mechanical Advantage
Output force (N)
MA Fo Fi
mechanical advantage
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
    adjust the mechanical advantage of the lever.

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
    radius of the wheel to the radius of the axle.
  • The wheel and axle move together to move or lift
    loads.

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
    advantage?

20
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

21
MECHANICAL ADVANTAGE
  • Complete Your Turn problems on p. 215
  • Complete Skill Sheet
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