1Impulse-Momentum-Impacts• Momentum: “quantity of motion”– Any object which has both mass and a velocityis said to have momentum. M = m.v(units of measurement: kg.m/s or N.s)Momentum and Impacts• Momentum is an especially useful measurement in describing the outcomes of collisions or impacts between two or more objects.• Remember - momentum depends on two quantities:– Mass– Velocity2• During impact/collision situations in sport, we often want to manipulate the momentum of at least one of the colliding objects to produce some desired outcome of the collision.•Examples:– Baseball• “swinging away” vs. laying down a bunt• catching a ball stiffly vs. “giving” with the ball– Volleyball• attack vs. dink– Soccer• Trapping (controlling) the ball vs. shooting on goal Conservation of Momentum• “The total momentum of any given system will remain constant unless acted upon by an external force.”or• The momentum before a collision is equal to the momentum after a collision.3Example: Bowling• Momentum of ball (before): MV• Momentum of pins (before): m0• Momentum of ball (after): Mv• Momentum of pins (after): mV()()()()mv m v mv m vball ballbeforepins pinsbeforeball ballafterpins pinsafter+=+***Link to Kinetics***• Impulse-momentum relationship (a very useful form of Newton’s 2nd Law): – Impulse = product of net force and the time over which the net force is applied (ΣF.t)Impulse = Change of MomentumΣF.t = ∆m.vΣF.t = ∆m(vf–vi)ΣF = ∆m(vf–vi)/t4ExampleHard landing: dissipating a large force over short time (∆t = 0.20 s)Soft landing: dissipating a large force over long time (∆t = 0.60 s)A 50 kg gymnast dismounts from the vault and sticks her landing.If she impacted the ground at a speed of –3.75 m/s, how would landing technique affect the forces she experienced in coming toa stop? Other common examples of this relationship:• Example Problems– How does the impulse-momentum relationship influence vertical jumping performance?– Do you think landing technique is related to lower extremity injury? Why or why not?– From a standing position, rapidly squat down and hold this position.• Draw the net force vs. time profile of this motion• Compute the impulse generated during this task.– How do airbags help reduce the severity of many automobile