## Sunday, January 31, 2010

### Application: Glogster

Kinetic friction is when an object is in motion while static is while the object is stationary. Using Newton's first law to find out why static friction is more than kinetic friction check out my glogster, click here!

## Tuesday, January 26, 2010

### Reflection Circular Motion and Gravitation

From this unit I have learned many things, I have learned new equations, I have come to better understand how/why objects move and have come to understand forces better. One of the first things we learned about were periods, these are a little tricky but help greatly in the problem solving procedure. They help with finding the velocity, in the beginning of the problem you are given how many rotations a minute or a second an object makes. You would then convert this to Hertz and then to seconds.

I have also learned about how objects move in circles. For example when an object is moving in a circular motion the velocity vector is tangential because it is always changing direction. The objects accelerations is always directed toward the center of the circle. So therefore in circular motion and objects acceleration is always perpendicular to it's velocity.

I have also learned what keeps the objects moving in a circle. To keep the object moving a centripetal force must be applied, this is not one specific force but rather could be any, i.e. friction of gravity. When objects move in vertical circles the centripetal force is different. Usually at the highest point of rotation the object centripetal force is equal to the force keeping the object in the circle plus the gravitational force then set equal to the mass times the velocity squared over the radius. At the lowest point the equation is the same but you subtract the gravitational force. But that is not always the case, depending on the way the forces are going you could have two equations for subtraction.

In some problems the forces are in different places. Problems that have to due carnival rides often have their forces in very different places, but still spin in a vertical motion. In these problems the firiction force can be in the upper y-axis and the normal force in the x-axis. Because of where the forces are you wouldn't necessarily solve the problem with the equations I stated above. You might do a sum of the forces in the y-axis or use the centripetal force equation. Overall there is no equation set in stone that you use to solve vertical circle problems. You have to evaluate your problem, draw an FBD, and choose that best method/equation to solve for with the facts you know. To sum it up the equations motions of vertical circles is different then horizontal ones.

I have also learned about 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" or the Law of Universal Gravitation sums it up perfectly. With this. This helps me figure out the what the gravitational pull between two object is or their masses or the distance between the two.I have also learned to find the acceleration due to gravity with any object.

This unit has been one of the most challenging for me. I have had to learn many new equations and how to use/when to use them. I have also have had to be very carefully with my fingers since I have been calculating big, long numbers. Again slowing down and reading the problem completely have lead to some mistakes in my work. I have also learned to make time in my day to review my notes even when there is not a test or quiz.

Gravitational problems have been hard for me because of the big numbers and to solve it is not also plug in the numbers but I have to go through steps or think about how to solve, that it is not just the given equation at the beginning of the notes.With this unit my finger skills have become much better. When I do not get a problem correct I check to make sure I have calculated correctly first.

My study habits have become better, with studying not just when needed. But as always my need to slow down and really read the problem has come into play. Also making sure I really understand the material and am not just solving the problem to finish it. I still need to work on things like slowing down, reviewing , and being careful in my work but I'm getting better with all of these things.

I have also learned about how objects move in circles. For example when an object is moving in a circular motion the velocity vector is tangential because it is always changing direction. The objects accelerations is always directed toward the center of the circle. So therefore in circular motion and objects acceleration is always perpendicular to it's velocity.

I have also learned what keeps the objects moving in a circle. To keep the object moving a centripetal force must be applied, this is not one specific force but rather could be any, i.e. friction of gravity. When objects move in vertical circles the centripetal force is different. Usually at the highest point of rotation the object centripetal force is equal to the force keeping the object in the circle plus the gravitational force then set equal to the mass times the velocity squared over the radius. At the lowest point the equation is the same but you subtract the gravitational force. But that is not always the case, depending on the way the forces are going you could have two equations for subtraction.

In some problems the forces are in different places. Problems that have to due carnival rides often have their forces in very different places, but still spin in a vertical motion. In these problems the firiction force can be in the upper y-axis and the normal force in the x-axis. Because of where the forces are you wouldn't necessarily solve the problem with the equations I stated above. You might do a sum of the forces in the y-axis or use the centripetal force equation. Overall there is no equation set in stone that you use to solve vertical circle problems. You have to evaluate your problem, draw an FBD, and choose that best method/equation to solve for with the facts you know. To sum it up the equations motions of vertical circles is different then horizontal ones.

I have also learned about 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" or the Law of Universal Gravitation sums it up perfectly. With this. This helps me figure out the what the gravitational pull between two object is or their masses or the distance between the two.I have also learned to find the acceleration due to gravity with any object.

This unit has been one of the most challenging for me. I have had to learn many new equations and how to use/when to use them. I have also have had to be very carefully with my fingers since I have been calculating big, long numbers. Again slowing down and reading the problem completely have lead to some mistakes in my work. I have also learned to make time in my day to review my notes even when there is not a test or quiz.

Gravitational problems have been hard for me because of the big numbers and to solve it is not also plug in the numbers but I have to go through steps or think about how to solve, that it is not just the given equation at the beginning of the notes.With this unit my finger skills have become much better. When I do not get a problem correct I check to make sure I have calculated correctly first.

My study habits have become better, with studying not just when needed. But as always my need to slow down and really read the problem has come into play. Also making sure I really understand the material and am not just solving the problem to finish it. I still need to work on things like slowing down, reviewing , and being careful in my work but I'm getting better with all of these things.

## Sunday, January 10, 2010

### Newton's Second Law

Newton's Second Law has been the toughest for me to understand out of the three laws. Newton’s Second Law helps us understand moving bodies by linking the cause and the effect (or force and acceleration) in a definite way. In the definition of Newton's Second Law it states that acceleration of an object is proportional to the net force and inversely proportional to the mass of an object. I found that very confusing until I learned the equations a=ΣF/m and ΣF=ma. These equations are the key to understand Newton's Second Law. The equations and FBDs helped me solve problems that involved gravity, tension and applied force. After mastering the equations I came to understand how things are inversely proportional to each other. For me though it was not just knowing when which equation or knowing what forces to use, but understanding why I would use each force/equation in a problem. This I think helped me get a better understanding of the second law. I may understand Newton's Second Law now, but I did have trouble mastering it. I have found a number of things difficult about the second law. One thing that I found hard was the direction the object was moving. If an object is moving upward the tension force (the force is usually tension) comes first in the equation. But when the object is moving downward the gravitational force comes first. In the beginning I did not understand this; I thought one force comes first no matter what. But after I came to understand that the direction the object is going affects the order the forces in the equation this problem was fixed. Another thing I had a bit of trouble with was inclined plans, I again had to refresh myself on SOH CAH TOA, but after that angles and inclined plans were a breeze. Just because I have survived this class for 1/2 a year does not mean I go without mistakes, my problem solving skills are stronger but not bullet proof (yet). I again have to remind myself to SLOW down. I have tendencies to rush through the problems as fast as I can. But I have gotten much better at slowing down reading the problem, thinking what I know, and using that information to solve. FBD's have been another small problem for me, in some problems I neglected to draw one. Since making many errors I have learned to make and FBD for every problem, even if not required to help. The making of an FBD helps show me how to set up my equation the right way.

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