Week 9: That darn dent

I don't-slash-can't drive yet.

And I'm okay with that--I'm in no rush to get behind the wheel. Because I know that once I do, I would have to worry about drivers who do not stop to think about others. *cough*jerks*cough*

Exhibit A here serves two purposes for this blog:

1) It supports the view that I have stated above. 2) It shows us an example of momentum and its conservation in a collision.


Exhibit A



This dent, shown here, belongs to my father's Honda Accord. Fortunately, my father wasn't anywhere near his car at the time of collision. He parked the car at...um, I don't really remember where he was when this happened, so let's pick a place that men usually frequent...Home Depot? All right, so my dad parked his car at Home Depot, got out and went inside the store. After half an hour, he returned (carrying whatever he went in to buy), only to find that someone *cough*jerk*cough* had dented his car.

Momentum is the product of an object's mass and velocity. When two objects collide, the total momentum of the system is conserved.

My dad's car, with mass 907 kg, was stationary so its initial velocity was 0 m/s. Therefore, it had zero momentum. The inconsiderate driver may have been driving at 10 mph (4.4704 m/s--Is this the average speed limit in a parking lot? If it is, good. If not, let's just pretend that it is.) with a total mass of 1800 kg. After the collision, the two cars "join together" and move at the same speed So...how fast were the two cars moving after the collision?

My dad's Accord and the cuplrit's car were moving at 2.97 m/s. (-->)

This is an example of an inelastic collision because, while momentum was conserved, total kinetic energy was not. The total kinetic energy of the system decreased after the collision and the lost energy was probably converted to others forms--sound (I'm pretty sure that the collision caused some form of noise) and heat.

The dent on the car also shows the concept of impulse (J). Impulse, the change in momentum, is the product of force and time of the impact or collision. Impulse is constant because momentum is conserved. This means that if t increases, then F decreases. And if F increases, t decreases.

The dent in the car shows that the material "gave" or allowed for t to increase in order to lessen the force of the impact. If the car was made of a harder substance that does not easily dent, then the magnitude of the force would have been greater.

And that means more damage and more money. But that wouldn't be such a bad thing if, you know, all drivers were considerate. My dad wouldn't have had to pay for the repair all by himself (with the help of insurance, of course) if the inconsiderate driver had at least left him a note with an apology, and his/her name and number.

I mean, come on. If you know that you dented someone's car, how can you just drive away as if you didn't? That does not make any sense. And it probably never will make sense to me, even when I do start driving. I just know that I wouldn't be so inconsiderate.

And, voila, the Physics of that darn dent.

Week 7: Swinging the boredom away

For the past week or so, I've been dreaming about Physics. More specifically, about tension. I dreamt several times that, for some reason, I had to find the tension of some type of rope or string or I don't know what, but I just knew that I was supposed to find the tension and I was freaking out because I couldn't and, and, and....then I woke up. Is this what you call a Physics nightmare?

Ah, but on to more pressing matters: the jellybean flavor of the week!

This past week's new flavor--or flavors, actually, because there were three--were ENERGY, WORK, and POWER.

To illustrate these three concepts, I'm going to take a step back, leave ScienceWorld, hop over to NonScienceLand, and on to the foreign and fascinating country of Speech and Debate.

The Hawaii Speech League kinda-but-not-really-officially kicked-off the new season on Saturday, October 2, 2010 at Le Jardin Academy. It was the first debate tournament of the season.

Now, it is imperative that you understand that all speech and debate tournaments are NOTORIOUS for being late. For the past couple of years that I've been participating in the speech and debate circuit, I have never been to a tournament that ran right on schedule. Never. Ever. And this happens for many reasons, of course, but those don't really matter; just know that tournaments never really follow the schedule.

So, on that particular Saturday up at Le Jardin, after debating about nuclear weapons, offshore oil-drilling and US military presence around the world for three consecutive rounds, the tournament was, as usual, running late. The 'Iolani debaters found themselves extremely bored, to say the least, during the time period between the end of the third round and the awards assembly. While tournament officials tabulate and sort ballots and decide which teams won, the debaters wait. And wait. And wait. And wait.

Some debaters from another school were prepared--they brought playing cards. Some of us from 'Iolani brought homework (I brought Physics homework! ;P) but not enough to last the whole waiting period. So, with homework already done, we literally had NOTHING to do but talk to each other, eat, listen to our iPods, dance and lip sync as we listen to our iPods, sleep, and/or take pictures.

Then, we found something we are deprived of in 'Iolani: A SWING SET.

Don't they look like they're having so much fun? Well, maybe not Darwin--he looks scared.


First, all four debaters (from left to right: Zeke, Darwin, Josh, Ayami) did negative work as they pushed off of the ground to start swinging. The net force applied by the debaters went one way (toward the ground at an angle), but they moved backward in the opposite direction (toward the sky in the same angle).

As the debaters swung back and forth on the swing set, their individual total mechanical energies stayed constant. Each time they swung back to their highest point, they each had a certain magnitude of initial potential energy and zero initial kinetic energy. As they swung forward and reached their lowest point perpendicular to the ground, they had a magnitude of final kinetic energy that was equal to the magnitude of their initial potential energy while the final potential energy is zero.

At one point in the debaters' swing fest, Darwin got tired or something and he couldn't swing as high as the others were swinging (maybe he was scared to go that high, I don't know). So Josh actually had to get up and push him so he didn't feel so bad about himself.

Before Josh pushed him, Darwin had a certain magnitude of power. When Josh got up to push him forward, the net force applied on Darwin increased, therefore increasing work done and also increasing his power.

 

Josh: "Darwin, you're too heavy..."

Just for funsies, here are a couple more pics of the swing fest:

Darwin: Someone get me off this thing...help...

Several minutes later, we were called in for the awards assembly.

And, voila, the Physics of swinging the boredom away.