light

Diamonds are cut in certain ways to allow light to pass through the top, reflect internally, and pass through the top again.  The diamond can reflect light internally because the light is moving from a high index of refraction to a low index of refraction.  For the light to reflect internally the light has to be at an angle greater than the critical angle of the diamond.  If the light is at an angle that is less than the critical angle the light will pass through the bottom, resulting in a badly cut diamond. 

ch.16-18

The ukulele produces notes by plucking the strings.  Each string has a different frequency when it is plucked.  Holding down the string a fret shortens the wavelength, which increases the frequency so the note is higher than playing the sting open.  The higher up you place your finger on the fret board the higher pitch note you hear because you are increasing the frequency of the note. 

magnets

The magnets in my electric toothbrush help me to clean my teeth everyday.  The magnets in the toothbrush provide a magnetic field that is used for the motor.  When I turn on the toothbrush, a current runs through the coils of the motor in a path that is perpendicular to the magnetic field.  If the current is not perpendicular to the magnetic field, the coil will not feel the maximum force.  However, if the current in parallel to the magnetic field, the coil will not feel a force at all.   Without the magnets, the head of my toothbrush would not rotate.

blog 8 torque

This pencil has a net torque of zero because it is able to balance on the ruler.  This means that the counterclockwise torque is equal to the clockwise torque.  The weight of the eraser and the metal on one side of the pencil requires a shorter radius to match the torque of the other side because T=Fr.  The larger the force is on one side the shorter the radius needs to be to equal the torque on the other side.  Physics is fun!

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.