Linear Momentum

1
Linear Momentum

• M mv
• measure of the quantity and direction of the
  motion of a body
• measure of a bodys persistence in its state of
  motion

2
Linear Impulse Ft

• Force x time of force application
• greater F or longer t greater change in M
• Impulse-Momentum equationFt M2 - M1

3
Shock Absorption

• landing from a jump or catching a ball require
  limb flexion to cushion impact
• Gradual stop --gt M force x TIME
• Sudden stop --gt M FORCE x time
• GRF in downhill running more than uphill
• GRF in high and low impact Aerobics

4
Change Direction Ft

• new Ft in a different direction required
• quickest change large F for small t
• less massive person change easier

5
Ft and Acceleration

• Acceleration can only occur if F-motive is
  greater than F-resistive
• longer t of motive F application MMM
• preparation phase in jump, throw, strike
• increase t of force application during the
  execution phase

6
Ft Momentum in Human Motion

• For shock absorption, spread the force over a
  long period of time
• e.g. catching, landing pits
• For quick starts, fast running/skating, etc.
  apply a LARGE force for a short period
• study on world class university sprinters

7
Collisions- implement/projectile

• resultant v of projectile depends on
• 1. Ft applied by implement
• 2. Elastic recoil capabilities of projectile
• impact time on projectile is brief (.001 to .005
  sec.)
• therefore F must be LARGE

8
Tennis Racquet Ball Collision

• each receives equal/opposite Ft from other
• v change for ball is large - smaller m
• ball stops, deforms, accelerates away
• v change in racquet is small - larger m
• racquet slows but does not stop _at_ impact
• total M of ball/racquet same after impact since M
  lost by racquet is gained by ball

9
Human Body Collision

• Conservation of M means each body in a collision
  will experience a change in M
• change in M will be in the form of a change in
  the v of each body
• less massive person will experience a greater
  change in v - sudden stop

10
page 396 Basic Biomechanics 4th edition by
Susan J. Hall
Head-on CollisionTwo Players Player 1m
90kg v 6 m/s Player 2m 80kg v 7
m/sResultant v after collision0.12 m/s in the
direction of 80kg player
11
Kinetic Energy KE ½ mv²

• Energy ability to do work
• Kinetic Energy ability of a body to apply force
  to move or deform another body
• squared v makes this component important
• higher up greater a downward
• faster forward greater impact