Oops...

This weekend was a weekend full of concerts and rehearsals for me. I started with a 2 ½ hr Youth Symphony rehearsal on Friday night, a rehearsal and concert for our school’s orchestra from 3-8:30P.M/ on Saturday, and another rehearsal/concert for Youth Symphony from 11:30A.M to about 9:00P.M. (yeah, I was pretty busy). Through all this one of my most important tools is my Getzen Custom Series 3047AFR trombone. I bought it in 10th grade and its been my main concert horn ever since, travelling with me to Kaui and Japan. When I first got it, it was nice and shiny, and although it still is fairly nice and shiny, it is now showing the signs of “heavy use.” Scratches are somewhat unavoidable, but also present on my trombone are dents both big and small. The largest dent is on the top of the main tuning slide. It dropped from the top of my trombone on a really hot day once (the hotter it is, the sharper your instrument gets. For example at ideal conditions your note A might be at 440Hz, but on a really hot day, the A played in the same position might be at 444Hz). The tuning slide had a potential energy of about (0.75kg)(9.8)(1.5m)=11.025J. When it hit the ground, all the potential energy was converted to kinetic energy. The velocity at which my slide hit the ground was thus about 5.42 m/s. When the slide hit the ground, there was an impulse between my slide and the ground. Since I did measure the velocity of the tuning slide immediately after it bounced off the ground or the time it stayed in contact with the ground (No, I did not drop and dent my slide in the name of science!), I cannot calculate the impulse, but I can conclude that the impulse was strong enough to leave a sizable dent in my brass tuning slide (brass is actually quite malleable). So I guess every time my trombone gets new “battle scars,” I’ll be thinking about physics!


My trombone doesn't look like this anymore =( (image courtesy of Getzen Co.)

Toys > Cleaning

I was cleaning up around my house the other day because it was getting to the point where I had to climb over stuff to walk through the living room, and I found a toy I received as a gift a few years ago. Since cleaning isn’t exactly fun, I decided I’d play around a bit with this toy. This toy consists of a wheel with magnetic tips that rolls along two metal rods. The wheel is held to the rods because of ferromagnetism. When you place the wheel on the rods and tilt it, the wheel will begin to roll along the path of the rods (see video 1).



Tilting is required to move the wheel because the force from the weight (mass*gravity)needed to overcome the inertia, or tendency to resist changes in motion, of the wheel. Once in motion, the wheel accelerates until it hits the bottom point of the rod. Assuming I started the roll from the top of the rod (holding the rod perpendicular to the ground), the wheel will have a potential energy equal to the mass of the wheel multiplied by the height of the rod. Because of conservation of energy, the kinetic energy of the wheel while at the bottom of the rod will therefore be equal to the potential energy of the wheel while it was at the top of the rod. In an ideal situation, the wheel would then be able to rise to the same point it started after it turns around for an upward motion. My wheel does not rise to the same level again at the second try, however (see video 2). This does not disobey the conservation of energy because energy was taken away from the system by friction (there is rotational friction between the wheel’s tips and the rods).



Because mechanical energy decreases due to friction each time wheel goes back up, the wheel reaches a progressively lower height. To keep the wheel moving, you must keep tilting the rod in a way that allows gravity to provide force to the wheel to replace the energy lost from friction. The lower you tilt the rod, the greater the y-component of force from weight, and thus the greater the speed of the wheel. As you can tell from the video, I was so blown away by the sheer awesomeness of this toy that I didn't bother to finish cleaning the house. I'll finish that...soon.