At the beginning of class, those of us who didn’t turn in our kinematics pair check on Monday turned it in before class started today. We didn’t turn in our homework (Kinematics Problems #1); instead, Coats-Haan passed around answer keys to check our homework. After checking our homework and asking any questions we had on the assignment, we looked at a worksheet called “Following Jack” This worksheet was designed to show the student the relationship between position and time in relation to speed. Afterward going over this sheet, the class began to take notes. The notes today were on position vs. time and velocity vs. time graphs.
For position vs. time graphs, the slope of the figure represents velocity. If a positive value on the graph is positive, the object is to the right of the origin (0,0) and if it’s negative, the object is to the left. Basically, if the object, such as a line, is pointing up, it is positive and similarly, if it is pointing down, it is negative. If the slope is positive, the object is moving right; if the slope is negative, the object is moving left. In either case, if the line is straight, the object maintains constant speed. If the position curve is a flat line, the velocity is zero. Also, a vertical position line, with a slope undefined, is meaningless. That basically means at one time you are in multiple positions, which Coats-Haan says isn’t possible unless maybe if you’re God. On a position vs. time graph, a line that is not a straight line means that the velocity is changing.
For velocity vs. time graphs, if the velocity is 0, the object is moving. If the velocity is positive, the object is moving to the right and if the velocity is negative, the object is moving to the left. This is just like the idea stated earlier that anything above the axis is positive and anything below is negative. If the line on the graph is curved, the acceleration isn’t constant. On these types of graphs, a line that is horizontal and straight means that the object has constant speed. Likewise, if the line is pointed up or down, the speed is changing. I don’t really understand this, but if a line is pointed down, that may mean that the object is speeding up. If the line is pointed up, that may mean the object is slowing down. An easy way to determine this is to draw tangent lines (short dotted lines) along the line or curve. If the subsequent lines have a steeper slope, that might mean the object is accelerating and if they have less-steeper slopes, the object is accelerating less. Unlike the position vs. time graphs, you don’t know where the object’s position is; therefore, when asked to tell where the initial position is, you say you don’t know, unless you are given the position in the problem.
By the time we finished going over these notes, we got out a page in our lab manual (I forget the page number). The page had a number of different position vs. time graphs and velocity vs. time graphs. Coats-Haan passed out matchbox cars to the class and in between Stedman getting carried away and constantly dropping his car on the ground, she had us act out the line in each graph with the cars. When we got to a graph that showed, I think, an instantaneous change in speed and direction, Coats-Haan said never to do that with our real cars. At that moment, Jacob was about to tell a story about the time he got into an accident at church, but Coats-Haan got the class’s attention before he could tell us what happened.
After we had finished this page, we barely had five minutes for Coats-Haan to pass out and explain a lab we were going to do. The lab is called “Graphing the Look of Motion” where you are supposed to use a sensor attached to the computer to detect your movement and have the program graph out the motion in both position vs. time and velocity vs. time graphs. The most the class could do at the end of the period is use the sensor to get a feel of how it works.
Tonight’s homework is to complete a worksheet called “Graphing Exercises.”
The question of the day is: You are chasing a truck full of chicken nuggets that keeps going faster and faster. Describe the position vs. time and velocity vs. time graphs for the truck’s motion.
Answer: In the position vs. time graph, the line, from the origin, is curving upwards, is moving right and is positive. In the velocity vs. time graph, I think the line is straight but I don’t know if it is pointed upwards or downwards. I’m guessing it is pointed upwards. If that’s the case, the line is moving to the right and is positive. Also, since it’s not stated in the problem, I don’t know where the origin is for this line.
No comments:
Post a Comment