1. 2 Kinetics Study of Motion Internal Forces: generated by muscles pulling via their tendons on...
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1. 2 Kinetics Study of Motion Internal Forces: generated by muscles pulling via their tendons on bones, and to bone-on-bone forces exerted across joint
2 Kinetics Study of Motion Internal Forces: generated by
muscles pulling via their tendons on bones, and to bone-on-bone
forces exerted across joint surfaces External Forces: acting from
without, such as the force of gravity or the force from any body
contact with the ground, environment, sport equipment, or opponent
Focuses on the various forces that are associated with a
movement
Slide 3
3 Calculating Moments of Force Moment arm is the shortest
(perpendicular) distance from the axis of rotation to the line of
action of the force Moment of force is influenced by the magnitude
of moment arm and the magnitude of the force Moment of Force =
Moment Arm x Force Moment of Force = Moment Arm x Force By grasping
the wrench at the end (A) a greater torque is generated because the
moment arm is greater than in (B)
Slide 4
4
Slide 5
Torque n n In any object experiencing torque, the distance from
the pivot point (the lug nut, in this case), to the area where
force is being applied is called the moment arm. n n On the wrench,
this is the distance from the lug nut to the place where the
operator is pushing on the wrench handle. 5
Slide 6
Torque n n Torque is the product of force multiplied by moment
arm, and the greater the torque, the greater the tendency of the
object to be put into rotation. The fact that torque is the product
of force and moment arm means that if one cannot increase force, it
is still possible to gain greater torque by increasing the moment
arm. 6
Slide 7
n n This is the reason why, when one tries and fails to
disengage a stubborn lug nut, it is a good idea to get a longer
wrench. Likewise with a lever, greater leverage can be gained
without applying more force: all one needs is a longer lever arm.
7
Slide 8
n The same concept can be applied to your lab on Monday with
the length of the hinge point away from the force of the weight.
8
Slide 9
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Slide 10
A lever is referred to as the simplest mechanical device that
can be called a machine (an instrument for performing work) Every
moveable body, whether acting alone or with others, is part of a
lever system that facilitates movement. 3 Classes of Levers: Class
1 Lever: (Eg The Teeter-totter) Class 2 Lever: (Eg The Wheelbarrow)
Class 3 Lever: (Eg The Snow shovel)
Slide 11
Fulcrum: (or pivot) The point at which the lever rotates. Load
Arm: The distance between the load and fulcrum Effort Arm: The
distance between the effort and fulcrum The way in which a lever
operates is dependant on the type of lever. CLASS 1 CLASS 2 CLASS 3
(Least Common) (Most Common)
Slide 12
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Slide 13
Everyday uses of Levers 13
Slide 14
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Slide 15
Factors affecting the moment of force A. Balanced teeter-totter
C. Increasing the applied force by adding a friend B. Increasing
the moment arm by leaning backwards D D 15
Slide 16
Ideal Mechanical Advantage of a Lever n IMA= Length of input
arm Length of output arm Length of output arm 16
Slide 17
Pulleys n Consists of a grooved wheel with a rope or cable
looped around it n Changes the direction of the force depending on
whether it is fixed or movable n A fixed pulley has an ideal
mechanical advantage of one 17
Slide 18
Movable Pulleys n If one end of the rope is fixed, and the
pulley(s) is allowed to move, you now have a movable pulley 18
Slide 19
IMA of a Pulley n The IMA of a pulley system is equal to the
number of support ropes 19
Slide 20
n Each segment of the rope that applies a force on the pulley
is considered a support rope. n Example: If you pull a rope with an
input force of 5 N, the rope applies this force to the movable
pulley n In the example on the right, you simply multiply the input
force by the number of strings. 20
Slide 21
n The last point of the previous slide can be summed up by this
n A fixed pulley will only output a mechanical advantage of 1, no
matter how many fixed pulleys you have in a system n There must be
a movable pulley present for an MA to exist. 21
Slide 22
n The mechanical advantage of a rigging that will require
upward pull can be determined by counting the number of rope
lengths running between engaged pulleys and those doing the work. n
Likewise, if the assembly will require downward pull, count the
ropes and subtract one to get the mechanical advantage number. n
The subtraction is necessary because with the fixed pulley, the
downward pull equals the load on the other length of rope so the
last "pull" rope does not provide any mechanical advantage. 22
Slide 23
A B C D A B C D A= mechanical Advantage of 1 B= mechanical
Advantage of 3 C= Mechanical Advantage of 4 D= Mechanical Advantage
of 5 23
Slide 24
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Slide 25
Wheel and Axle n Consists of a shaft or axle that is attached
to a larger disk, called the wheel n The effort force on the wheel
magnifies the load force on the axle n Examples: screwdriver,
steering wheel 25
Slide 26
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Slide 27
n Opposite occurs on a bicycle n A large effort of force is
applied to the axle to overcome the smaller load force on the rim
of the wheel n Advantage is that the wheel has to travel a farther
distance in the same amount of time 27
Slide 28
Wheel and Axle IMA If the input force is applied to the axle,
the IMA can be calculated by dividing the radius of the axle (r a)
by radius of the wheel ( r w) n IMA = radius of axle radius of
wheel radius of wheel If the input force is applied to the wheel,
the IMA can be calculated by dividing the radius of the wheel (r w)
by radius of the axle ( r a) n IMA = radius of wheel radius of axle
radius of axle 28
Slide 29
Inclined Plane IMA= Length of Ramp Height of Ramp Height of
Ramp 29
Slide 30
Wedge n Similar in shape to an inclined plane but used in a
different way n It is forced into an object to split it apart n The
wedge increases the force applied to the object to help split it
apart. 30
Slide 31
Screw n Is actually an inclined plane that winds around itself
n It helps increase the force you use by converting rotational
motion into a straight line very slowly. 31
Slide 32
Mechanism n Two or more machines working together. 32