Tuesday, January 25, 2011

Energy, "The Big Bucks"

          I woke up at five in the morning. Chugged me a RedBull, and prepared. Put on my shirt, jacket, pants, head cover, gloves, and all. I was all camo’d up and ready to roll. And as I walked out, I grabbed my new, Mathews Z7 Xtreme bow. Got the arrows all ready, grabbed my pack, and headed out. It was about a twenty-minute drive to the stand, my dad let me off a couple hundred yards away. I walked to the stand with my bow, climbed up into the tree, and waited for deer to show up. And as I was sitting there for hours on end in the dark, I began to fall asleep into a dream… about PHYSICS. In this dream, I was sitting in my stand waiting, but it was daytime now. A big huge buck of a lifetime, with 10 big long points, stepped out. I drew my bow back and then the dream froze. I knew that if I pulled this back and let go the arrow would fly and hit the deer, but I wondered how it works. Then, a certain person came to me in my dream; it was Mrs. Gende, the physics wizard. She explained to me this thing called ENERGY, and the CONSERVATION OF ENERGY. It was really interesting to learn about this “CONSERVATION OF ENERGY”. It helped me understand the true mechanics behind my bow.
          Now that I have woken up from this fantasy world of hunting, I understand what the conservation of energy is. One could think that it is quite confusing to find certain variables in an energy statement. But, once you learn that in conservation of energy that the initial and final energies are equal, it is quite easy. So, in this situation, if friction is negligible and my height is zero, we have both a initial and final energy chart. The initial is the bow at full draw (pulled all the way back), and the arrow in motion. There’s a lot to this concept so here’s a little thing to help you out.


Sunday, January 16, 2011

UCM Reflection!

In this unit we learned about UNIFORM CIRCULAR MOTION, or UCM. I learned about UCM in many different ways. We started out with easy stuff like the circumference and period, and then moved to a little more complicated things. We learned about the frequency, the tangential to the circle, the centripetal acceleration, the centripetal force requirement, and centripetal force. Ok, so, starting with the basics. UCM is the motion of an object with a constant (uniform) speed. For UCM to be possible, the object must be moving in: 1- A perfect circle where the radius does NOT change, and 2- with constant speed. Now for the parts of UCM. The circumference of the circle is the distance around the circle and the period is the time of one rotation in seconds. So if the circumference is 2πr and the period is T, you can conclude that v=2 πr/T. But, that is just the velocity. I also learned about the frequency which is f=1/T. The frequency is the number of revolutions per unit of time, and the unit is Hz. Now back to the velocity, even though in UCM the speed is constant, the direction changes. So the magnitude of the velocity remains the same but not the direction. And, the direction of a circle can be very confusing, so the way to find the direction is by finding the tangential to the circle. Now for another part of UCM, there is the centripetal acceleration. Centripetal means towards the center, so if the velocity is tangential to the circle, then the acceleration must be perpendicular in order for it to be towards the center. The centripetal acceleration is ac=v2/r. And last of all, we can find the centripetal force. There are many different centripetal force requirements; it can be tension, gravity, friction, and others depending on what the situation is. This requirement keeps the object moving in a circle. But, whatever different force the requirement is, you still use Fc=mv2/r. As you can see, in the equation, everything is related. The velocity equation is used to find the acceleration, and then the centripetal force equation is the acceleration equation with mass added to it. So everything I learned in this unit is all related to the end result of the centripetal acceleration.
            What I have found difficult about this unit is mostly the conceptual problems. I can do everything that is with numbers, but on the conceptual problems I can get kind of lost. I just feel like I have trouble understanding the science behind all of these parts of UCM, but when but into the context of a problem, I understand them perfectly. It’s hard to explain but I tried to give an idea.
            My problem skills have definitely been enhanced during this unit. I put a lot of effort into trying to understand more about circles. I have never really been good with circles but since we did labs and because of the demonstrations on the PowerPoint’s, I understand it much better. I never knew that you could relate the sizes of circles to time which then gives you velocity. I felt that distance in a circle, the time around a circle, and velocity would NEVER relate. But now with the equation v=2 πr/T, I now get it. I kept trying and trying the problems, and after all of that effort, I now understand all of the relations in UCM. I’m very good at solving for equations that require substitution such as substituting all of the equations into the net force equations on the vertical circle problems. If Ft=Fg, and Ft=Fc, but there was also a missing variable, I was able to find cancellations and eventually cancel out the missing components until I found the correct answer. And, like I said earlier, my weakness was in the conceptual parts. I was just kind of lost in those places. But now after the test, I understand what I did wrong and I’m working on fixing it. I now get why the speed is constant and the velocity isn’t. IT ALL MAKES SENSE NOW!!!
This Unit was really interesting and different than anything I’ve ever learned about circles. I hope to learn more about it and I hope I can use it to help me in other units!

Friday, January 7, 2011

Who You Gonna Call? Mythbusters! BUM BUM BUM BUM

In this lab, we decided to make physics extra extra fun... By using Mythbusters, my group had to bust two myths. It was a challenge, but in the end, victory was ours. We busted those bad boys. Now watch and learn.

Myth 1: An object always moves in the direction of the net force exerted on it.

First Reaction: This isn't required to write this but it is interesting. At first, when you look at the myth you think "uhh duhhh..." because your mind immediately thinks of a force applied. But, once you start analyzing this experiment and taking all of the other forces into the equation your mindset changes.

Prediction: If an object always moves in the direction of the net force exerted on it, then, by hitting the ball in the air it will prove it wrong because the net force is negative and the ball continues to move in a positive direction.

Procedure: Now, this was not the most complicated thing ever. All I had to do was hit the baseball up in the air. While I hit, Matt recorded, and then we analyzed the recording in order to see if our prediction was correct.


Equations for when I hit the ball:

Equations for after I hit the ball:

Outcome: Now, the myth states that an object always moves in the direction of the net force exerted on it. But.... it doesn't. Let's take a look. The ball is moving up and away from me after I hit it. If you were to pause the video after the ball leaves my bat you would see that air resistance and gravity are both in a negative direction. So, if the myth is true, my ball would be moving right back at me to hit me in the head. But, thank goodness, it did not hit me in the head. The ball continued up, positive, and away from me, positive. So, by comparing the FBD's to the video it is clearly shown that even though the net force is negative, the ball is moving in a positive direction. BUSTED!

Myth 2: An object always changes its motion if there is a force exerted on it by other objects.

First Reaction: Your first reaction when you see this myth is puzzling. You are trying to think of a way to bust it, but you are over thinking it. All you have to do is think simple. Most people would think about pushing a wall or something like that, but all you have to think about is simply a tennis ball being hit by a string. Just something small. Now let's see what we did.

Prediction: If an object always changes its motion if there is a force exerted on it by other objects, then, by having me run into Blaine, we will prove it wrong because my motion continues in the same direction.

Procedure: Again, quite an easy procedure. All I do is run into Blaine while Matt records the video. Then we analyze our video and decide if it is busted.


Equations as I hit Blaine:

Outcome: Ok, so, this myth states that an object always changes its motion if there is a force exerted on it by other objects. In our lab, I was the object in motion, and Blaine was the other object exerting a force on me. I was running at him, and then as I made contact the force applied from him was exerted on me. But even though he was applying a force on me, I continued in the same direction. So our lab straight up proves this lab busted. Another object exerted a force on me and my motion continued in the same direction. Myth number 2.... YOUR BUSTED!

Conclusion: We busted both of these myths. We know that they are definitely not true in every situation because in our experiments, they were wrong. But, if we did not bust the myth, it wouldn't necessarily mean that the myth is true. To prove something true, there must be no possible wrong scenarios, and with only one test you could not prove it 100% true.
Like I said earlier, everyone, even I, had first impressions of these myths. In myth 1, you're going to assume of course that if the net force is positive the object moves in a positive direction and if it is negative then a negative direction. It just sounds right if you don't sit down and think about all of the factors, you must know what is going on with the object at all time and that the net force is not always the same. The net force in an objects motion may change, and the motion may change. So, you cannot just eyeball this myth and assume that it is true. As for the second myth, I believe that the only reason why this myth could be misunderstood is just because of the way we live today. We will compare this myth to car wrecks or running into walls (hopefully nobody has run into a wall lately). For this myth you have to think of a scenario where it is big object versus little object or strong object versus weak object because sometimes, this myth can be correct, but it is not always, because we BUSTED it. Busting both of these myths was really fun. I enjoyed proving these easily misunderstood concepts wrong. It helped me understand why people seem to misunderstand it, and now I have enough knowledge to explain to people why this myth is untrue.

Well... that is it for this episode of Mythbusters. So next time there are some physics myths... WHO YOU GONNA CALL? MYTHBUSTERS!!!!