Linear Kinetics - continued. Ground reaction force in activities Runner … Increases stride over...
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Transcript of Linear Kinetics - continued. Ground reaction force in activities Runner … Increases stride over...
![Page 1: Linear Kinetics - continued. Ground reaction force in activities Runner … Increases stride over slow-moderate speed range Longer stride produces GRF’s.](https://reader035.fdocuments.in/reader035/viewer/2022072011/56649e0d5503460f94af6aa9/html5/thumbnails/1.jpg)
Linear Kinetics - continued
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Ground reaction force in activities
Runner … Increases stride over slow-moderate
speed range Longer stride produces GRF’s w/larger
counteractive horizontal components Longer stride lengths increases shock
transmission up the extremity ( stress on the knees)
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Ground reaction force in activities
High jumper Move with large
horizontal velocity with slight downward directed vertical velocity at stride before take-off
GRF reduces horizontal velocity & creates upward vertical velocity
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Friction
Acts at the interface of surfaces in the opposite direction of the motion
Unit: N Magnitude determines ease/difficulty
of motion Example:
R
Fa
Fs
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Friction
Maximum static friction (Fm)
Kinetic friction (Fk) – constant magnitude friction generated between two surfaces in contact during motion
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Friction
What factors determine the amount of force needed to move an object?
Coefficient of friction () interaction between two surfaces Unit-less Relative ease of gliding Influencing factors?
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Friction
Normal reaction force Greater the force, greater the friction Can we decrease the reaction force?
Can we reduce or increase the friction? Alter the coefficient of friction? Examples???
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Friction in everyday life
Does greater contact area generate more friction?
Shoes/feet & surface interface
Rolling friction: deformation during contact Influenced by weight, radius & deformity Bike tires
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Friction
Effect of fluid? Synovial fluid Speed skating Bowling ball
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Collisions
Momentum: the quantity of motion that an object/body possesses Product of mass and velocity
M = mv
m = 80 kgv = 7 m/s
m = 90 kgv =6 m/s
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Collisions
Momentum Principle of conservation of momentum
…..in the absence of external forces, the total momentum of a system remains constant…
M1 = M2
m1v1 + m2v2 = (m1 + m2)(v)
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Collisions Impulse: product of a force and the
time interval over which the force acts
Impulse = Ft - from Newton #2
F = ma F = m(v2-v1/t)
Ft = (mv)2 – (mv)1
Ft = M
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Collisions
Impulse examples