Blog 7

While I was doing my essays and studying for the many test that I have this week I got bored and started twirling the my earphones in a vertical circle and realized that the earphone jack was experiencing centripetal force.  The earphone jack wants to continue in a straight line, but the tension in the cord pulls the earphone jack towards the center of rotation.  Although the earphone jack is being pulled to the middle of the circle, it actually feels like it is being pushed out of the circle.  It feels the centrifugal force which is equal to the centripetal force.  The earphone jack feels the lightest at the top of the circle when T=mv2/r-mg, medium at the side when T=mv2/r, and the heaviest at the bottom when T=mv2/r+mg.

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.

blog 4: friction

Friction is a factor in almost everything we do, even simple things like moving my calculator.  If was fairly easy to move my calculator, so that means that it has a small friction coefficient and a small normal force because friction=(friction coefficient)(normal force).  To move the calculator my push force had to be greater than the maximum static friction.  Moving the calculator from a rest position took the most push force.  After I overcame the maximum static friction the calculator moved and it took less force to keep it moving.  Once the calculator was moving, my push force had to be greater than the kinetic friction.  The kinetic friction of any object is always less than the maximum static friction.  Friction is fun!

inertia

We went to my friends house to play ping pong and eat food.  While we were playing ping pong we could rely on inertia to keep our food, bowls, cups, and ping pong paddles at rest.  Newton's first law says that if an object is at rest, it wants to stay at rest and if an object is moving, it wants to keep moving.  The food, bowls, cups, and ping pong paddles were at rest and stayed at rest.  The objects are applying a force on the ground, but its normal force balances out the force that is applied back towards the objects.

projectile motion in bowling

I noticed that bowling balls go through projectile motion when I went bowling this weekend.  It does not matter if you toss the ball in the air or if you just use horizontal velocity, the bowling ball still goes through projectile motion.  While in the air the bowling ball will maintain the same horizontal velocity (disregarding air resistance) and its vertical velocity will have a negative acceleration of -9.8 m/s/s.  The bowling ball is only in the air for a short moment because I do not release the ball at a high distance or at a large positive angle.  The ball is in the air for a moment, follows projectile motion, then lands on the lane, and heads for the pins.  Strike!

football

This weekend I played a football game against Damien. I experienced changes in velocity, acceleration, distance traveled , and displacement.  Before the play starts I am standing still with a velocity, acceleration, distance traveled, and displacement all with values of zero.  Once the play starts I begin to move forward with a positive acceleration and velocity.  As I stutter my feet to make a cut, I have negative acceleration and my velocity decreases.  I begin to run again with positive acceleration and my velocity increases.  After I catch the ball I continue to run slightly gaining positive acceleration and increase of velocity.  Once I am hit by a defender, I have negative acceleration and my velocity decreases to zero.  After that play is over, my distance traveled and displacement are positive values.  Throughout that play I demonstrated physics through changes in velocity and acceleration,  positive distance traveled, and  positive displacement.