Tuesday, December 7, 2010

What do Mμ know? Newton's Laws!!!

What do mμ know? Well that is the wrong question to ask because this is about what I know. I learned so much about Newton's Laws. The book states "An object at rest tends to stay at rest and an object in motion tends to stay in motion blahblahblah...", I had no clue what we were learning. But then, we began with the problems, and I started to learn about this thingy called Inertia.


We started off with the easy stuff like Fg=mg,  ΣFx=0 and ΣFy=0, and "mickey mouse" problems like that. Then we applied that to normal force, then we found the net force, and I thought it was easy. But it got a little bit harder, but a lot more interesting. I learned how to apply these small equations to trigonometry and I was then able to find other forces such as tension. Starting off with the translational Equilibrium Equations,  ΣFx=0 and  ΣFy=0, combined with a FBD, I could use the small equations that we learned to find the missing force in an equation. If I was told that a block was hanging by two cords, the block was 50 Newtons, and the angles of the cords were 60 degrees, I could easily find the tension in the cords. Then, we had problems that had more forces such as friction and force applied. We used the FBD's to clarify these problems, we applied  ΣFx=0 and ΣFy=0, and after many calculations, we found the missing force. And though the problems slowly got harder and harder, I was able to apply all of the small concepts that we learned and trigonometry to find the missing variable. I learned a TON about the first law. And I was told that this was the hardest law, I was able to wipe the sweat off my head. I learned many things about Inertia and his first law, I had all of the forces down, and was ready to move on to the next law. 

Newton's second law was definitely in my top 3 favorite laws of motion. (That's funny because there are only 3!!! So I liked all of them!!!). Ok, back to the reflection, I got carried away in the awesomeness of the laws. According to the book, the second law states that "for a particular force, the acceleration of an object is proportional to the net force and inversely proportional to the mass of the object." Now in not super smart terms, it is saying that the net force equation is equal to the mass multiplied by acceleration. So  ΣF=ma. Though I still had to draw FBD's and apply all of the rules that I learned in the first law, it was very different. Now, the net force equation was not equal to zero. Also, we had to use our old equations from projectile motion and horizontal projection. We got to use the good ol' yellow sheet. With the second law, we were given a situation where a certain object with a mass is either lifted, propelled, or moved by applied force. We would set up the net force equation to equal mass times acceleration. After having everything set up, we would solve for the missing variable, which was usually acceleration. These problems also started off simple, just regular algebra applied to physics. But then, we had to apply this law to other concepts. One of the concepts we had to apply this to was apparent weight. We had to apply the regular first law, and then we had to use the second law to finish off the problem. They were problems like finding the normal force in a elevator if the elevator is accelerating (either up or down). So in order to find this, we would have to combine the two laws. We would have to use the  ΣF=ma equation, but we would have to take into perspective that we are finding the normal force of the elevator on the person, and not the tension force or anything else. We also had to apply the second law to pulley systems, the biggest change was instead of  ΣF=ma, it was  ΣF=mtotala. I learned to draw two FBD's and then I was able to relate the FBD's together depending on the pulley system. I would find the positive and negative forces, make the net force equation, and solve for the unknown. This concept can be very confusing if you over-think it, but I learned if you highlight the direction of the motion, make the net force equation, then solve for the unknown helped greatly. The last concept we applied this to was frictional force. In this concept we were introduced to our new friend Mu. Otherwise known as μ. The equation for friction is Ff=Fnμ. I learned how there is kinetic and static friction in this topic. Kinetic, or sliding friction, according to the book, occurs after the starting friction and is usually less than the static friction. The static friction, or starting friction, according to the book, occurs between surfaces at rest relative to each other. In some of the problems, we were given both μstaticand μkinetic. We had to decipher between each on some problems but on others we just had to find the missing force. In order to find the frictional force, you must have μ and Fn. So, using the ΣFy=0 equation, we would find Fn, and then apply it to the Ff=Fnμ. It was pretty simple to learn, and the concepts are pretty simple to apply. Learning about μ, the coefficient of friction, was very interesting and I enjoyed it.

 Newton's third law was short and sweet. The book states that "when one object exerts a force on another object, the second object exerts on the first an equal force in opposite direction." So in an easier way, if the head hits the wall, the wall hits the head. (Hopefully nobody is hitting a wall with their head, it is just an example). So all in all, it was just an action force has a reaction force.

What I have found difficult about Newton's Laws is very simple. I know all of the laws, I know how all of them work, and I can get most of the problems. I just don't know exactly when to apply some of the rules. I find it difficult to know when to use certain net force equations. I usually get it right, but sometimes I am a little bit "iffy". The last thing that I had difficulties with some of the angles on the tension problems in the first law. Sometimes I don't know which axis to draw my x component and y component to, sometimes I draw the right triangle with the y-axis, and sometimes with the x-axis. I don't know if one is right or if they are both but that is what I found difficult. I got most of the stuff and understand it well, but just these two little things were confusing

The laws of motion have really upped my level of thinking. My problem skills have gotten SO much better. I really put a lot of effort into trying to understand everything in the first place. Getting the simple FBD'S was pretty easy, but then applying them to the problems was the hard part. After applying them to the problems, I felt that my strengths were finding ways to get to the final answer. For example, some FBD's might not give you enough information so that you can cruise through the problem. On these harder problems, my strength was that I was able to find my way to the end. I was able to plan ahead and see that a certain variable was going to cancel out, which would then make the problem much easier. It is very hard to explain in words, but it was just simply my thought process was my biggest strength. I gave a very good effort with all of the laws and tried as hard as I could, and other than making complicated FBD's with angles, I got pretty much everything and understood it well.



  1. Your reflection is excellent, very thorough and clearly explained.
    Please remove any mentions of my name as it is out of context. The objective of reflections (and all of our blog postings) is not to talk about the teacher but about your learning process. For example, you could say: "in class we learned how to highlight the direction of ..."
    Remember that you have an audience not just your teacher!
    Is there a way that you can format your posting so that the words are not cut at the end of the column?
    Great job!!

  2. This comment has been removed by a blog administrator.

  3. I apologize for the last comment, but I can't figure out how to delete it. You have done a remarkable job of fixing the formatting, which makes it easier for the reader to notice your stellar writing style. One problem I had with the posting is that you misspelled 'cord' several times, which led me to believe we were talking about music. Although this made tension force much more interesting, the quality of your post would be much improved if you changed this. Overall, I was glad to read about your views of physics class, and look forward to your next posting.

  4. I removed your comment for you, Abigail. I changed all of the chords to cords as well. Thank you for pointing that out to me!
    Thanks for the comment.