Monday, December 7, 2009

Newton's First Law


This is what I learned about Newton's First Law.  Also known as the Law of Inertia, Newton's First Law states that an object at rest will stay at rest and an object in motion will stay in motion unless acted upon by an unbalanced force.  In this scenario, the object has the potential to change direction, slow down, and speed up.  When an object is at rest, the sum of the forces in both the x and y axes equals zero.  When this happens the object is in equilibrium, also known as translational equilibrium. In order to solve many problems where forces act upon objects, you must separate forces into x and y components.  This is important when forces, including gravity, act upon the object at an angle other than 0, 90, 180, 270, or 360 degrees, where the force would not be associated with an axis.  In order to find the resultant vector you use the Pythagorean Theorem (R=sq. rt. (A^2 + B^2).  Substitute A and B with Sum of the X and Sum of the Y.  To find the direction of the force you use the equation tan^-1 (Sum Y/Sum X)*absolute value.  Using the calculated Resultant Force you can find the mass by Fg = mg.  I also learned that the Equilibrant and Resultant Forces have the same magnitude and mass, but are in the opposite directions (a difference of 180 degrees).  This is what I have learned about Newton's First Law, Inertia, and Forces acting upon objects.

What I have found difficult about what I have studied is setting up the equations to find the x and y components of forces.  I need to develop more skill in this area so that I can be more time efficient.  Whenever I stumble upon a problem, I always have to stop and go through my SOH CAH TOA, and see which one makes sense.  This process takes me more time than I would expect of myself, and commonly after I finish the problem I second guess my work, or feel uncomfortable.  Whenever I am required to find the x and y component of gravity I have to analyze the force very closely.  Also, whenever I am given an angle of a force in a problem I am forced to think of which angle is actually relevant to the problem.

I feel that my problem-solving skills are generally pretty good.  I often find myself getting frustrated, setting aside the material, and then coming back to the work where I have an epiphany, or an "AhHa!" moment.  From then on, I try to build my confidence and I commonly make up my own problems, or re-do the problems in the homework or class work.  I feel that I help myself understand the problem further by making myself visuals such as FBD's or other sketches.  I have a hard time memorizing equations with variables, and I have found a way that has made me be successful.  Whenever I am introduced to a new equation, I take a few minutes to look at the equation and try to understand its purpose, meaning, and why it works.  By doing this, when I am introduced to a foreign style of problem I have a higher chance of knowing which equation to use.


The physics we are learning in class can be transferred into our understanding of our natural world around us.  Engineers use physics and Newton's laws when designing tables, lifts, and motors.  The engineers must calculate the strength of the material or device in order to build a special race car, cable-stayed bridge, or a hydraulic car lift.  Also, when we are in a car crash our bodies want to continue in our current direction, when there is another force causing the car to slow down, speed up, or change direction.  It is this abruptness that causes injuries in car wrecks due to whiplash, and sudden changes in velocities.  When I walked into school this morning, I opened a door applying pressure as far from the hinge as possible because then the force would be the most effective.


  1. Great reflection! I can clearly see the effort you put into learning the material, and you know that hard work pays off.

  2. I liked how you connected what we are learning in physics class to the real world that surrounds us. Nice!!

  3. Same do I. Racing Cars as an example of physiks?! Amazing idea. Further I can totally see your "struggles" the memorization. I had similar problems but the blue sheet helps a lot!