LEVERS

1
LEVERS
2
Definition Concept

• Lever is a simple machine which operates
  according to the principles of moment.
• Lever is a rigid bar which can rotate about a
  fixed point when a force is applied to overcome a
  resistance.

3
Definition Concept

• Lever A bar that is free to move about a fixed
  point
• Parts of a lever
• Fulcrum The fixed point of a lever
• Effort Arm The part of the lever that the
  effort force is applied to (measured from the
  fulcrum to the point at which the force is
  applied)
• Resistance Arm The part of the lever that
  applies the resistance force (measured from the
  fulcrum to the center of the resistance force)

4
(No Transcript)
5
(No Transcript)
6
Function of Lever

• Lever perform two important functions
• They are used either to overcome a larger
  resistance than the effort applied.
• OR
• To increase the distance a resistance can be
  moved through by applying greater effort than the
  resistance.
• Note When there is no motion, the effort turning
  effect equals the resistance turning effect, and
  the lever system is said to be balanced.

7
Lever Arms

• Lever arms are commonly defined as the portion of
  the lever between the fulcrum and the force
  point.
• The effort arm is the distance between the
  fulcrum and the effort point.
• The resistance arm is the distance between the
  fulcrum and the resistance point.

8
Mechanical Advantage

• By using the length of the effort arm and the
  resistance arm we can find the ideal mechanical
  advantage.
• Ideal Mechanical Advantage (IMA) if there were
  no energy lost due to friction the
• IMA length of effort arm le
  .
  length of resistance arm lr

9
There are 3 types of levers

• 1st Class Levers
• 2nd Class Levers
• 3rd Class Levers

10
1st Class Lever

• The fulcrum is located between the Fe and the Fr.
  First class levers can multiply force and
  distance.
• Examples Scissors, see-saw

11
2nd Class Lever

• Resistance is located between the effort force
  and the fulcrum. These levers multiply the force
  but the direction stays the same.
• Example Wheelbarrow

12
3rd Class Lever

• The effort force is located between the fulcrum
  and the resistance. The effort arm is always
  shorter than the resistance arm so it cannot
  multiply the force and the MA is always less than
  1.
• Examples Rake, hockey stick

13
Principle of Lever

• A lever of any class will balance when the
  product of the effort arm and effort equal to the
  product of resistance arm and resistance.
• This is known as principle of levers.
• It enables us to calculate the amount of effort
  needed to balance a known resistance.

14
Cont.

• If any three of the four values are known the
  remaining one can be calculated by using the
  following equation.
• E x EA R x RA
• Where E Effort
• EA Effort Arm
• R Resistance
• RA Resistance Arm

15
Cont.

• A lever whose effort arm is longer of the two
  whether it be a Ist or IInd class lever, is said
  to favor force. (Less effort is required to
  overcome a resistance )
• Conversely, a lever whose resistance arm is
  longer, whether it be a Ist or IIIrd class lever,
  is said to favor speed and distance.

16
Relation of Speed to Range of Movement of Levers

• In angular movement speed and range are
  interdependent.
• For instance if two IIIrd class lever of
  different length moves through a 40 degree angle
  at the same angular velocity, the tip of the
  longer lever will be traveling a greater distance
  than the tip of the shorter lever.

17
Cont.

• Since both the lever is traveling their distance
  in equal time the longer lever must be traveling
  faster than the shorter lever.

18
Selection of Lever

• Skill in motor performance depends upon the
  effective selection and use of levers, both
  internal and external.
• Long golf clubs are selected for distance and
  shorter clubs for accuracy at close range.
• Heavy base ball bats are chosen by those with
  good strength whereas children are often taught
  tennis with short handled racquets

19
Cont.

• In most instance the external levers are designed
  for a specific purpose and are selected
  accordingly.
• Whereas the levers in the human body are not
  designed for one action or purpose, so the sports
  person must use his body parts as a lever as per
  the requirement.

20
Cont.

• Shorter body levers increases angular velocity
  while the positioning of body parts to form a
  long position favor linear speed and range of
  motion.

21
Identification and Analysis of Levers

• For identifying a lever one should find the
  following answers
• What is the location of the fulcrum
• Where is the effort point and where is the
  resistance point
• What is the length of effort arm
• What is the length of resistance arm
• What are the relative length of effort and
  resistance arm
• What kind of movement does it favors

22
Levers QuizUse the following slides to quiz
yourself on how how well you can match commonly
used items with their correct class of lever.
23
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class3
24
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
25
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
26
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
27
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
28
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
29
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
30
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
31
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
32
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
33
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
34
Chose the correct Lever classification for the
tool pictured below.
Class 1 Class 2
Class 3
35
END