Linear Momentum

M = mv

measure of the quantity and direction of the motion of a body

measure of a body’s persistence in its state of motion

Linear Impulse = Ft

Force x time of force application

greater F or longer t = greater change in M

Impulse-Momentum equationFt = M2 - M1

Shock Absorption

landing from a jump or catching a ball require limb flexion to “cushion” impact

Gradual stop --> M = force x TIMESudden stop --> M = FORCE x time GRF in downhill running more than uphill GRF in high and low impact Aerobics

Change Direction: Ft

• new Ft in a different direction required

• quickest change = large F for small t

• less massive person = change easier

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

Ft Momentum in Human Motion

For shock absorption, spread the force over a long period of time

e.g. catching, landing pitsFor quick starts, fast running/skating, etc. apply

a LARGE force for a short period study on world class & university sprinters

Collisions- implement/projectile

• resultant v of projectile depends on:1. Ft applied by implement2. Elastic recoil capabilities of projectile

• impact time on projectile is brief (.001 to .005 sec.)

• therefore F must be LARGE

Tennis Racquet & Ball Collisioneach receives equal/opposite Ft from other v change for ball is large - smaller mball stops, deforms, accelerates away v change in racquet is small - larger mracquet slows but does not stop @ impacttotal M of ball/racquet same after impact since M

lost by racquet is gained by ball

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”

page 396

“Basic Biomechanics”

4th edition

by Susan J. Hall

Head-on CollisionTwo Players

Player 1:m = 90kg v = 6 m/s

Player 2:m = 80kg v = 7 m/s

Resultant v after collision:0.12 m/s in the direction of 80kg player

Kinetic Energy: KE = ½ mv²

Energy = ability to do workKinetic Energy = ability of a body to apply force

to move or deform another bodysquared v makes this component importanthigher up = greater a downwardfaster forward = greater impact