blog 6: momentum

Last week we played Kaua`i High School for Division II semi-finals.  Momentum is conserved in a collision between the ball and me.  I run a route and Reece throws me the ball, if i catch the ball it is a sticky collision; however if i drop the ball it is a bouncy collision.  This pass was a sticky collision that ended up in a touchdown. The equation for a sticky collision is m1v1i +m2v2i = (m1+m2)vf.  The collision is a sticky collision because there are two objects that combine masses after the collision and travel at the same final velocity.  If I were to drop this pass the equation for a bouncy collision is m1v1i + m2v2i = m1v1f + m2v2f.  In either situation momentum is alway conserved!

Blog 5: change in engergy

Everyone drops stuff.  An object at rest at a distance above the ground has a positive potential energy value (mgh) and a kinetic energy value of zero (1/2m(v)(v)).  Once I released the pencil, its potential energy started to drop and its kinetic energy started to rise.  Right before the pencil hits the ground all of the potential energy has changed into kinetic energy.  The kinetic energy right before the pencil his the ground is the same value as its potential energy at the top because of the law of conservation of energy.  However, the pencil does not bounce back up to its original position because most of its energy is converted into heat, sound, transfered to the ground, or other converted into other energy.