Round and Round

It has become a tradition in the Bassett household to go to the fair as a family every fall. As a kid, I always knew we were on the fairgrounds when I could see the ferris wheel poking out for everyone to see. Well, being at boarding school, I missed the fair at home, but was able to go to the mountain fair in Asheville. Like always my mind was drawn to the ferris wheel that overtakes the night sky. Looking back on that day now, I see how I could have applied physics to this very scenario. As we learned, rotating objects will have both rotational velocity and tangential velocity. No matter where you are sitting on the ferris wheel, you will always have the same rotational velocity, which is equal to your rotations per minute. The ferris wheel will rotate the same number of times no matter what. But imagine that there was another row of seats, a row that was closer to the center, or, if you look at the picture, closer to the green area. These two different rows would have different tangential velocities. Tangential velocity measures the distance that you go in a certain time frame. Well, the row closer to the middle would have to cover less distance in a certain amount of time because it is closer to the axis of rotation. The outer row would have to cover a larger amount of distance in the same amount of time because it is much farther away from the axis of rotation. Now, every time the Bassetts go to the fair, all I will be thinking about is the Physics of a ferris wheel.

Starting Off With a Bang

        Well, we are certainly off to a strong start in the spring semester of Physics. It was definitely hard to come back since we had truly done no work, but the experiments we preformed and the lessons we learned certainly made it a lot easier.
        Ms. Lawrence started class off by asking us a question, "Which person will go faster, the person on the outside horse of a carousel or the person the very inside horse of a carousel. Instantly, my brain shut down. How were we supposed to know this? It was beyond any knowledge we had learned before. Thankfully, Ms. Lawrence explained to us that the answer can be answered in two ways. To answer the question, we had to look at both the rotational velocity and the tangential velocity. We learned that rotational velocity was measuring the rotations per minute, and tangential velocity measured the distance covered in a certain amount of time. In the case of rotational velocity, both people were going the same speed. However, when we examined the tangential velocity, we came to realize that the person on the outside was moving faster. This is because they had a greater amount of distance to cover in the same amount of time that the inside horse did. To give an example, recall the propeller experiment we preformed on the first day back to class.
     Next, we watched a video on rotational inertia, and the conservation of rotational momentum. Recall that inertia is the property given when an object resists change in motion. Rotational inertia is basically the same thing with one difference: it is the property given to an object when it resists change in spin. This property is dependent on mass and the distribution of mass. If there is more weight towards the outside of the axis of rotation, then the object will be harder to turn. As an example, think of how runners bend their knees when they are running; this brings the mass closer to the axis of rotation and will ultimately decrease the rotational inertia. Next we have the conservation of rotational momentum. We figured out that rotational momentum is equal to the rotational inertia multiplied by the rotational velocity. We also came to the conclusion that for momentum to be conserved, the rotational momentum before would have to equal the rotational momentum after. We set this equation up just like we did last semester for the conservation of momentum. To learn about the conservation of rotational momentum, we watched a clip on a figure skater pulling her arms in when she spun, causing her to speed up. We figured out that when the figure skater has her arms and leg extended, the rotational inertia will be larger, causing the rotational velocity to be smaller. Looking at the opposite spectrum, when an ice skater tucks her arms and legs in, she decreases her rotational inertia which will ultimately cause her rotational velocity to increase.
       The next subject we talked about was torque. We said that torque caused rotation, and was equal to the force multiplied by the lever arm; the lever arm is just a fancy way to say the distance from the axis of rotation. The larger the lever arm is, the greater the torque will be. To go along with this, we also learned about center of mass and center of gravity. The center of mass is the average position of the total mass on an object or objects. The center of gravity is when gravity is working on the center of mass. Finally, we said that when an object is in a state of balance, it is because the counter-clockwise torque is equal to the clockwise torque.
      Finally, we learned about centripetal and centrifugal force. Centripetal force is a center seeking force; it is what keeps you moving into a curve. Centrifugal force is defined as a center fleeing force, but in reality isn't actually a force at all. It is used to describe that feeling you get when your driving into a curve, like you are about to be flung out of the car. In actuality, there is no force that does this to you.
      I think the biggest challenge coming into this semester was trying to reprogram my brain back into a Physics-thinking mode. I had been so used to thinking mindlessly during break that is was a shock to come back to the classroom. However, my classmates and Ms. Lawrence made it easy on me by taking a slow start and building up from there. We also talked over questions we had.
       In this first unit of the new semester, I feel like my problem-solving skills and effort have increased. I talk more in class and help my partners during labs. I even try to explain to other people that are confused what is going on. My patience has also improved. It is easy in homework questions to try and simply get everything done. However, in reality it pays more to put forth effort, and think through questions that might be confusing. While this definitely increases the time it takes to finish exercises in the book, it is worth it. Second, I feel that as an individual and as a class, our communication skills have improved. We make sure to ask questions when we have them, and even inquire from our neighbors about concepts we don't understand. Finally, I feel that I have started to be more creative in physics, as I think about every day things that pertain to the units we are learning at the time.
      

The Great Mass of a Meter Stick Challenge

        It was a momentous day when Physics F Block walked into class and heard the words "I've got a challenge for you guys today," and a challenge it certainly was. After studying in class lessons on torque, rotational inertia and velocity, and the conservation of angular momentum, we were given the task to calculate the mass of a meter stick only using a 100g weight. Tricky right? My brain exploded just a tad. In my head I was thinking, "How on earth can I do this?!" Thankfully, my partner Margaret Anne had more of a cool head than I did (being a red head has disadvantages sometimes). We thought about the lesson we had just learned on torque, and got to work.
      So thinking about torque, we need to realize that it is equal to the force multiplied by the lever arm; the lever arm is a fancy way of saying the distance from the axis of rotation. We also know that torque causes rotation. Finally, we know that when an object is balanced, like say a see-saw, the counterclockwise torque is equal to the clockwise torque. Thinking this through, we decided that the best step would be to find the lever arm of the meter stick. So, we balanced the weight on the end of the meter stick, and pushed it toward the end of the desk until it was in a balanced state. The meter stick was level at twenty-two inches. We know that a meter stick equals one hundred centimeters, so we could therefore subtract twenty-two from 1one-hundred, and we got seventy-eight.
      Now it got a little tricky (like it hadn't already); we needed to find the lever arm of the other side of the meter stick. To do this, we needed to know the center of gravity, which on a meter stick will always be around fifty centimeters. From there, we subtracted fifty from seventy-eight, and got that the second lever arm would be twenty-eight centimeters. We had all the measurements we needed, but now we had to plug these numbers into an equation.
        As we said before, we know that when a meter stick is balanced (like it was) the clockwise torque is equal to the counterclockwise torque. This gave us an equation to plug our measurements into. Like we said before, we know that torque is equal to the force multiplied by the lever arm; accordingly, our equation became counterclockwise lever arm x force= clockwise lever arm x torque. We said the force on the first side was the weight, so we multiplied that by our twenty two centimeter lever arm. On the opposite side we multiplied our twenty-eight centimeter lever arm by our unknown force. Once we plugged the answer in, our unknown force was 78.57.
         We measured the meter stick and got around 83 grams, which is pretty close to our actual answer. While it was a tough process, it was interesting to use physics to way something without using a scale. It was a good way to wake up our brains in the morning.

Cats and Physics, who knew they had anything in common!

So, when you first watch this video, it is completely understandable that there might be some people out there scratching their heads and thinking, "What did I just watch?" Honestly, if I had not been in a physics class I would have thought the exact same thing, but that was before we learned about the concept of torque. Torque is the name given to the property that causes something to rotate. To get torque, you can multiply the force and the lever arm together; the lever arm is just a fancy way of saying the distance from the axis of rotation. So putting this video into context, we saw the doorstop that the cat was playing with. Based on torque, we know why that doorstop was placed at the very end of the door instead of somewhere in the middle. This was done to increase the distance from the hinge, ultimately increasing the lever arm and thus the torque.

Ice Princess

So I think I probably know what you are thinking right now, "What on earth does a cheesy Disney movie have to do with our physics class." Well, as Margaret Anne and I were talking about in class, Ice Princess is the story of a girl who does a physics project on ice skating. So, to compare this to physics: we know that angular momentum is equal to the rotational inertia multiplied by the rotational velocity. As we talked about in class, when someone spins on skates, whether it's one the ice or at a roller rink, it will always be easier to spin faster when you have your hands and leg tucked in. This is because when you do this, more mass is distributed to the center of the axis of rotation. When this happens, we know that rotational inertia will be less than if you spread your leg and arms out, causing the mass to distributed towards the outside of the axis of rotation. Accordingly, because the rotational inertia is less, then the rotational velocity will be greater causing the skater to go faster.