I had a great weekend. Friday night after class I went home and spent some time with my folks (get psyched for a fantastic “Stories by Dad D” tomorrow). I got a hair cut and then spent some time with my sister, a friend, and the Schenk crowd. It was a very social day. I loved it.

Sunday I went climbing with Mark and Irene then spent three and a half hours battling advanced dynamics with a team of students.

Let’s get our geek on!

The problem was such:

A person fires a bullet into the air at angle a and an initial velocity of i cos a + k sin a (the projectile is being shot south). Solve for the position of the projectile when it lands taking into consideration the influence of the angular acceleration of the Earth on the projectile. Disregard air resistance.

Diagram anyone?

Although a huge pain in the butt, I think we figured it out. What made it mildly interesting is that the distance of the particle from the center of the Earth is changing for the duration of its air time. So the angular acceleration has to be a function of the particle’s height.

### 20 thoughts on “Full speed ahead”

• 10/2/2006 at 10:16 am

OOHHH!!! I know this one! I saw this on CSI one time. The bullet will end up in the chest of some dudes wife with an 85 degree entrance vector. I’m glad I was able to help with this one.

• 10/2/2006 at 10:37 am

I heard a loud “whoosh” as that problem flew over my head. Since we’re disregarding air resistance, I think that the projectile will not land at all. It will continue, unchecked, into outer space.

• 10/2/2006 at 10:51 am

Ahh but while air resistance can be ignored, Gravity is still in the mix. Although in our problem we assumed Gravity was constant. But with distance, I suppose that too would be changing. it’d be interesting to see what would happen if we re-did the problem using gravity as a function.

• 10/2/2006 at 10:58 am

This question is flawed – if there’s no air HOW DOES THE GUNPOWDER IGNITE, HUH?

Ha! Take that, physics!
(I always preferred Chemistry, anyway)

• 10/2/2006 at 10:59 am

if i and k are large enough, it would get into outer space!

sadly, i think i’ve forgotten completely how to solve these problems. maybe, if I’m put in a group with Mike D, it’ll all come back and we can rock the bullet problems… but on my own… I think I’d be stuck.

• 10/2/2006 at 11:08 am

Ok, now explain the effect of the loss of air resistance on gravity. I say air resistance is a big help in slowing the velocity to the point where gravity can pull the projectile to the ground. Where’s the balance in forces? How does kinetic energy play off of gravity? This is getting complicated.

• 10/2/2006 at 11:50 am

There’s air, it just doesn’t resist anything.

This air just gives in.

• 10/3/2006 at 9:17 am

You don’t need air to ignite gunpowder, it doesnt require air as an oxidizer, its purely a chemical reaction that can happen in a vacuum.

• 10/3/2006 at 4:38 pm

Just part of the magic!

• 10/6/2006 at 11:15 am

I think I can safely speak for most Americans in stating that the answer to this problem is “Who cares?” Unless someone we know was holding the gun, or hit by the bullet (assuming it hits anything) we won’t lose sleep over this one.

• 10/6/2006 at 11:30 am

Not only does it live, it thrives! It’s growing. It’s taking over the world. But no one really gets excited about that.

• 10/6/2006 at 11:33 am

Of course they don’t, because they don’t care.

• 10/6/2006 at 11:37 am

Thank you Jes Saint for making my point again. I thought it was implied. But there are those who believe you can never state the glaringly obvious too many times.

• 10/6/2006 at 11:47 am

Did you sit on a cactus this morning?