FoxTrot Classics by Bill Amend for June 29, 2010

Hit by a car flung from the catapult he and Marcus built, no doubt …

Yeah, but a loving father on the run to the hospital only hears the worst of it.

Also a somewhat clueless father like Roger (alas) with a daughter like Paige (double alas).

Leave it to Paige to give out wrong information

Nabuquduriuzhur

Wha?

@Nabuquduriuzhur

Huh?

No, Paige was correct. Jason DID get hit by a car. Just not the one that Roger would imagine. He ran out of the house not listening for the ‘other stuff’ which was probably the explaination of what type of car.

@Nabuquduriuzhur Huh?

Do Paige and Jason really have the same genes?

You’d be surprised how you can improve the velocity of a Hot Wheels car by using a slingshot.

I’m no engineer, and I only have a 9th grade education. But I know he (Nabuquduriuzhur ) is discussing potential and kinetic energies.

I nearly failed Physics, Nab hurt my head! :)

I like Jason and Paige (and Peter too, just cuz he’s not in the this panel doesn’t mean he doesn’t exist :)) because they show just HOW different siblings can be - I mean, these three have NOTHING in common except mom and dad!

bird I got the math. It’s the last paragraph that kinda lost me.

I learned something today. Ain’t wasted. Thank you NABetc.

I won’t pretend to understand the math. I think he was just pointing out how confusing it can get using different conversion methods. As I’m not at all familiar with those methods, I’m not sure.

Mass = potential energy

Mass x velocity = kinetic energy

Am I on the right track?

Was the Hot Wheels car on the wrong track?

@ Nabuquduriuzhur… You are Jason all grown up, aren’t you? :)

Nabuquduriuzhur said: “(hoping I got the terms/values in the right spots in the second part. I was rather quick and sloppy! The final value is correct as are the final units.)”

Hi Nabuquduriuzhur,

Well, as a matter of fact, no you didn’t, and no it isn’t.

To relate pounds (force) and slugs (mass) on earth where the acceleration due to gravity is (about) 32.2 feet per second per second, one slug (mass) (at rest) has a force on it due to gravity of 32.2 pounds.

So something that ‘weighs’ one quarter pound (force) has a mass of (one quarter divided by 32.2) slugs, or (1/128.8) slugs, which is 0.007762 slugs.

Now, go figure out your answer taking that into account.

Kinetic Energy = (1/2) times M times (V squared)

( And by the way 90 miles per hour is 132 feet per second, not 135. )

So the kinetic energy would equal (1/2) times (1/128.8) slugs times 132 times 132.

Or 67.64 foot-pounds.

And then I seriously doubt that Paige could throw anything at a velocity of 90 miles per hour anyway.

(Although I certainly agree with your arguments against the metric system – the biggest collection of scientifically precise but practically awkward units ever devised by (French) man! But then people of EVERY country confuse units of mass and force for ‘weight’ because we all live on the earth where they are tied together by the acceleration due to the earth’s gravity!)

Ow. My head hurts.

thebird55 said, “Mass = potential energy

Mass x velocity = kinetic energy

Am I on the right track?”

Hi “thebird55”,

(What follows is a simplification to explain the principle of the thing WITHOUT getting bogged down in pointless niggling details! Other physicists need NOT nitpick the answer!!)

Mass by itself has no energy at all. Take a 1/32.2 slug mass rock (which happens to “weigh” one pound on earth - in round numbers). When it’s sitting on the ground it has no energy relative to the ground. Pick up the rock and climb the stairs to the top of a 1500 foot high building. It now has 1500 foot-pounds of potential energy (relative to the ground). Drop it off the side of the roof of that building. On the way down back to the earth’s surface, it will exchange that 1500 foot-pounds of potential energy into 1500 foot-pounds of kinetic energy as the rock falls. Halfway back down to the earth’s surface it has 750 foot-pounds of potential energy remaining, and 750 foot-pounds of kinetic energy because of it’s speed at that point of its fall. At the instant just before it hits the ground it will have 1500 foot-pounds of kinetic energy and no more potential energy. (This neglects the effect of air resistance on the falling rock just to keep things simple.) The instant after it hits the ground and comes to rest, it again has no energy. All your work that you invested in that rock by carrying the rock up the 1500 feet of stairs to the top of the building is gone! What happened to it? It got turned into heat upon the rock’s impact with the earth again. The atmosphere absorbs the heat and it gets dissipated to space.

Just for the record, back in the day when I dealt with metrics in high school chemistry and physics, I didn’t find them awkward - at all. Nabu’s excuses for the U.S. not switching over to the metric system strike me as just that - sophisticated excuses. If we’d just bitten the bullet when we had the chance (and I was studying the metric system right when we could’ve done so), we’d be used to it by now like our Canadian neighbors and nobody would be complaining about it.

We lost a probe to Mars because someone had to convert from the U.S. system to the metric system and forgot to do so. Inexcusible. Not the person’s action, the fact that such a conversion had to be made at all.

It’s been a long time since I’ve heard of slugs as a unit of mass - this may be only the second time.