Sunday, January 16, 2011

Universal Gravitaion and UCM or other words, gravity and things that go in circles


Definition - The motion of an object in a circle with a constant or uniform speed.

       Uniform circular motion does not have a constant velocity (due to direction change) and an ever-changing acceleration.  This acceleration due to the centripetal force. (centripetal means inward force that is applied to an object to keep it moving in circular motion, or towards the center.)  Circular motion depends directly on centripetal force and the centripetal force requirement depends on the force that keeps the object in a circlet.  The net force of centripetal force depends on the acceleration, and velocity as well. 


Definition (or the law of universal gravitation) - "every object in the universe attracts every other object in the universe with a force that varies directly with the product of their masses and inversely with the square of the distance between the centers of the two masses"

       The universal gravitation is the numeric value of 6.67x10^ -11 N.m^2/kg^2.  This figure is most commonly used in the equation Fg= (Gm1m2)/r^2


I have learned that there is an equation to find the gravity of other planets or imaginary places, but that I already at least new a little about.  The thing I learned that was the most 'enlightening' was learning about circular motion.  I did not know that uniform circular motion was always accelerating and I did not know that it did not have a constant velocity.  It does not have a constant velocity because although the magnitude is constant, the direction is always changing.  As our book tells me, this word that describes it is tangential.  Also with uniform circular motion there is period T, frequency, and acceleration.


What I have found difficult is remembering what equations to use, also I have trouble 'improvising' with things such as coefficient of friction but now, after studying for the test, I now understand what to do.  I also used to have trouble with ratios but not anymore (since I studied for the test.)


My problem solving skills have needed improving, I lacked some of the connecting to improvise and impute other equations when needed.  But since studying for the test, I feel like I have improved and understand more of what is really going on in these equations.  Some of my strengths are being able to solve with no problems when I have the equations.  An example is the ratios problem on page 106 in the blue notebook.  It asks to find the value of g if earth's mass was double but the radius remained the same.    I couldn't think of the equation to use.  It didn't occur to me to use the equation that Mrs. Gende gave me because I thought I needed to make a ratio problem.  I made a equation that worked for all the problems and some others that needed to be worked on the notes.  Later Mrs. Gende told me that it wasn't a good equation to use.  And to only use the equation g=GM/r^2.  But in this equation with G is equal to 9.8m/s (with mass as well so mass is canceled out) and when multiplying the other side of the equation is is 9.8m/s,.  The other problem was 43 on page 105.  And I used my equation that I made to solve this problem....  But after speaking to Mrs. Gende I tried that other equation and it worked as well, I was just trying to solve a problem and so I did what I could to solve it.

1 comment:

  1. Good reflection though there is no explanation about what exactly keeps an object in UCM. What is the centripetal force requirement? How do we determine the net force.
    There are a few misconceptions:
    The big 'G' is only a constant of proportionality for the universal gravitational law. As such it does have units. Please add the appropriate units.
    Later you state that the big 'G' is just 9.8 m/s^2 which is incorrect. Please see me to go over this material to clarify these items.