Basic College Physics
John.Quality
MOTIONHANDOUT1.docxMOTION HANDOUT
Working in your groups, discuss the following concepts or situations and explain with diagrams, words, mathematics, graphs, or examples.
1. What is motion?
2. What is position?
3. How do we determine direction?
4. What is change in position?
5. What is distance? How do we determine distance?
6. You travel from Dayton, OH to Cincinnati, OH. How would you determine your average speed? Put it a mathematical formula.
7. What is instantaneous speed? How is it different from average speed?
8. What is acceleration? Is a car traveling in a straight line at 35 mph an example of acceleration? What about a car traveling around a curve at constant speed?
9. Make as many formulas as you can from the following formula:
a = v/t, where v = vfinal – vinitial and t is elapsed time.
10. When a physicist says describe the motion of something, he or she means describe the velocity of the object or how it changes (speeds up, slows down, and/or changes direction).
11. When an object speeds up, slows down, and/or changes direction it is said to be accelerating. Acceleration is a description of velocity.
12. When an object speeds up in any direction, its velocity vector points in the same direction as the acceleration vector. When an object slows down in any direction, its velocity vector points in the opposite direction of the acceleration vector.
1. A car slows down moving north. What direction does its acceleration vector point?
1. A car speeds up moving in a negative direction. What direction does its acceleration vector point?
1. A car speeds up moving in a positive direction. What direction does its acceleration vector point?
d. If an object is not speeding up, not slowing down, or not changing direction, what is its acceleration?
Understanding position vs. time graphs, velocity vs. time graphs, and acceleration vs. time graphs.
The graph below is a one dimensional motion graph, which means that the motion of the moving object is always along a straight line regardless of what the shape of the graph is. For example, the following graph is the position vs. time graph for an object thrown straight up in the air and returning to where it started.
( t (s) y=0 y ( m) )
The vertical axis, which is nothing more than two long rulers placed end to end, plots the position of the object. Any position above the horizontal axis means that the objects place at any given time is above the y=0 position. The motion, however, is first positive (upward) then negative (downward). Notice that the object is never below the y=0 position. Obviously, the y=0 position is at the point of release of the object, say a person’s hand, and returns to that same position.
6. If the person had not caught the object, what would the graph look like? The instantaneous velocity vs. time graph is developed from the instantaneous position vs. time graph. In the example above, draw the instantaneous velocity vs. time graph look below.
( t (s) v=0 + v ( m /s ) - v ( m /s ) )
7. Now you will attempt the instantaneous acceleration vs. time graph. Just think about what the motion is doing on the way up and which way the acceleration vector is pointing and what the motion is doing on the way down and which way the acceleration vector is pointing. In this class, we deal with constant acceleration only (remember that when you draw your graph).
( t (s) a=0 + a ( m /s 2 ) - a ( m /s 2 ) )
8. A car starts from rest and travels south until it reaches 40 m/s. Draw the position vs. time, the velocity vs. time, and the acceleration vs. time graphs. Draw qualitative graphs only (no numbers). Assume constant acceleration.
