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!