[Lab Issues]

To find the net torque, recall that torque is force multiplied by distance when applied at a right angle. You know the radius of the disk, and the force applied (mg for your hanging mass)... use that to find your moment of inertia.

[The SAT Physics Subject Test]

I'm glad it went well and you thought that the book helped -- magnetism is one of the trickier topics in physics, and for many (myself included), you don't really "get it" the first or second time through.

Random Sports Response: I can't wait to see the 49ers and Steelers match up on the 19th!!!

[Adding impulse to injury]

Nice analysis. Good luck tonight and take it easy on that knee!

[Impulse and Momentum]

Excellent. How can you apply this to air bags in cars?

[Sport Science: What they didn't cover]

I'd love to see how he'd do against pro soccer players in that goal. :beaten:

[More Gymnastics Physics]

Great analysis up to the conversion to mph... 279 in/sec is roughly 16 mph.

[A Blog About Balls]

Excellent! Should have sent a video camera home with you!

[Spontaneous Combustion]

In my previous career as a microelectronic engineer, we regularly worked with a gas known as silane (SiH4), a pyrophoric gas, which means it ignites spontaneously in air. Even better, for safety reasons they kept it outside the building in a bunker, which I had a great view of from my office window. :livid: It's fun to look at some of the safety precautions used when dealing with pyrophoric gases... double contained lines, shut-off valves, etc.

[Physics of a Full]

Our study of rotational kinematics and moment of inertia will play a big role in understanding the gymnast's rotations from a physics perspective. From a performance perspective, it looks like magic to me!

[Just behind the curve.]

NOT uncommon at all. Physics takes time to sink it (that's why we try to end units and leave a few days for problem solving / practice / sink in before pulling it all together on an exam). I spent five years as an undergraduate learning how to make transistors, but didn't understand how one worked until I was a senior... some things just need to stew and sift for a while. :-)

[Freeze em]

nice... nothing says physics like blood and vomit on ice!

[So it turns out physics jokes are really lame...]

The following is an actual question given on a University of Washington chemistry midterm. The answer was so "profound"

that the professor shared it with colleagues, which is why we now have the pleasure of enjoying it as well.

Bonus Question: Is Hell exothermic (gives off heat) or endothermic (absorbs heat)?

Most of the students wrote proofs of their beliefs using Boyle's Law, (gas cools off when it expands and heats up when it is compressed) or some variant. One student, however, wrote the following:

First, we need to know how the mass of Hell is changing with time. So we need to know the rate at which souls are moving into Hell and the rate at which they are leaving. I think that we can safely assume that once a soul gets to Hell, it will not leave. Therefore, no souls are leaving.

As for how many souls are entering Hell, let's look at the different religions that exist in the world today. Some of these religions state that if you are not a member of their religion, you will go to Hell.

Since there are more than one of these religions, and since people do not belong to more than one religion, we can project that all souls go to Hell.

With birth and death rates as they are, we can expect the number of souls in Hell to increase exponentially.

Now, we look at the rate of change of the volume in Hell; because Boyle's Law states that in order for the temperature and pressure in Hell to stay the same, the volume of Hell has to expand as souls are added.

This gives two possibilities:

1. If Hell is expanding at a slower rate than the rate at which souls enter Hell, then the temperature and pressure in Hell will increase until all Hell breaks loose.

2. Of course, if Hell is expanding at a rate faster than the increase of souls in Hell, then the temperature and pressure will drop until Hell freezes over. So which is it?

If we accept the postulate given to me by Ms. Teresa Banyan during my Freshman year--"...that it will be a cold day in Hell before I sleep with you."--and take into account the fact that I still have not succeeded in having sexual relations with her, then #2 cannot be true; and thus I am sure that Hell is exothermic and will not freeze.

THE STUDENT RECEIVED THE ONLY "A" GIVEN

[So it turns out physics jokes are really lame...]

The Official Unabashed Scientific Dictionary defines a transistor as a nun who's had a sex change.

[So it turns out physics jokes are really lame...]

The following is a little known, true story about Albert Einstein (attributed to Paul Harvey).

Albert Einstein was just about finished his work on the theory of special relativity, when he decided to take a break and go on vacation to Mexico. So he hopped on a plane and headed to Acapulco. Each day, late in the afternoon, sporting dark sunglasses, he walked in the white Mexican sand and breathed in the fresh Pacific sea air. On the last day, he paused during his stroll to sit down on a bench and watch the Sun set. When the large orange ball was just disappearing, a last beam of light seemed to radiate toward him. The event brought him back to thinking about his physics work. "What symbol should I use for the speed of light?" he asked himself. The problem was that nearly every Greek letter had been taken for some other purpose. Just then, a beautiful Mexican woman passed by. Albert Einstein just had to say something to her. Almost out of desperation, he asked as he lowered his dark sunglasses, "Do you not zink zat zee speed of light is zery fast?" The woman smiled at Einstein (which, by the way, made his heart sink) and replied, "Si."

And know you know the rest of the story.

[WA gripe of the night]

The key here is realizing the force applied is horizontal... then, using the data you gave me, you can put it all together so your answer looks something like this!

[Torque and Auto Repair]

Absolutely! I wonder what other applications of the cross product we'll find this year... :frog:

[Life, Liberty and the Pursuit of Physics]

This is the reason we teach... students who care and want to learn. I'm thrilled you're seeing things differently, and can't wait to hear about what you uncover this year (and of course, let's make sure to talk about physics of the trombone when we get to sound and waves!!!)

[Physics of a Push-up]

Just thinking about how you could extend this, you could also calculate the work per pushup, or the power output. Then, of course, there are all the different types of pushups you can do... from diamond pushups to slide pushups to prison pushups... each designed to put your arms at different angles to work different muscles. Would be a great exploration into components of forces!

[Relative Velocity and Autopilot]

Go to your profile, then near the top of the screen, choose Forum Actions --> General Settings. From there you can find a setting for avatars.

Great thinking expanding from relative velocities to inertial navigation systems (INS). These are a core of F-16 (and other) military navigation systems. I have some friends who have done some work in this area, I'll see if I can't talk them into elaborating a little. :eagerness:

[Breast Cancer Awareness Month]

Very cool! Reminds of the question I heard a few weeks ago at Syracuse University. A teacher asked "what's the benefit of all this research at CERN?" The answer -- so far, CERN's particle research has resulted in the invention of the Internet as well as tremendous advances in radiation therapy... who knows what'll be next!

[Physics of breaking wood]

Great analysis. If you look, there are TONS of great physics/karate sites you can find in a Google search... I stopped looking at the fourth page of cool sites!

[Baseball and Bernouli]

Excellent... fluid dynamics even comes in handy in baseball!

[Making Up Numbers Is Fun...]

Of course, if you're stuck, you can always try the Homework Help forum...

[Making Up Numbers Is Fun...]

Slow down on the problem and take it piece-by-piece. Can you break up the vectors into their components?

[Physics Frustration]

Gladly. You can find all of our notes at http://aplusphysics.com/wordpress/apc/

Also, worked out solutions are available in the classroom, though for the future I'd avoid waiting until the last day so as to reduce your frustration and allow you time and opportunity to obtain help.