P=mv What could be manipulated in order to change the football player’s momentum? • Brick wall? • Dinosaur eating football player?
P=mv A change in momentum would mean a change in either the mass or velocity. We’ll always assume the velocity changes. What causes a change in velocity? a Force
Impulsealso known as change in momentum Impulse= (force)(time) = FΔt Unit is Newton-second N-s
Increasing Momentum“Follow through” in sports • Apply the greatest force possible for the longest time possible Impulse= (force)(time) = FΔt
Decreasing Momentum • http://www.hailstate.com//mediaPortal/player.dbml?DB_OEM_ID=16800&id=661846&db_oem_id=16800
Decreasing Momentum The change in momentum may be b/c of a small force exerted over a long time The change in momentum may be b/c of a large force exerted for a short time
Decreasing Momentum To minimize the effect of the force on an object involved in a collision, the time must be increased.
Other examples that decrease the force by increasing the time • Air bags • Catching a baseball with a glove • Fighting with padded gloves v. bare fists • Rolling with a punch Padded dashboards • Packing materials • Crumple zones • New seat belts
Practical application Observe that the greater the time over which the collision occurs, the smaller the force acting upon the object.
Cradling the ball • A water balloon is thrown high into the air and successfully caught. The key to the success is to contact the balloon with outstretched arms and carry the balloon for a meter or more before finally stopping its momentum. The effect of this strategy is to extend the time over which the collision occurred and so reduce the force. • This same strategy is used by lacrosse players when catching the ball. The ball is "cradled" when caught;
Other examples where extending your time decreases the force • Bungee jumping • Bending your knees when you jump, not locking them • Safety nets/ giant air mattresses (during fires, circuses)
Impulse Activity • Monday it is supposed to be 80 degrees • Good Luck!