November 19, 2008
Kinematics!

Today in class, we had a substitute filling in for Ms. Kozoriz and corrected the chapter 3 study guide. I'll post the answers up just in case anyone missed any blanks.

Position and Distance
An object's position can be described in terms of its relationship to a reference point. Choosing a reference point establishes a(n) frame of reference. Describing distance does not need a(n) frame reference. Distance involves only a measurement of length, and is a(n) scalar quantity. Position involves both distance and direction, and is a(n) vector quantity.

Average Velocity
If an object is moving, its position at one and only one time is a(n) instantaneous position. The change is position of an object is its displacement, which is a(n) vector quantity. The average velocity of an object is the change in position divide by the time interval over which the change occurred. Average velocity is calculated using the equation v=Δd/ Δt. In this equation Δd, which is read as "delta d", stands for displacement. the symbol Δt, which is read as "delta t", stands for time interval. Average velocity is expressed in a unit made up of a(n) distance unit divided by a(n) time unit. Different units used to describe average velocity can be change can be changed from one to another by the use of conversion factors.

Finding Displacement from Velocity and Time
Displacement can be caculated by using the equation Δd= v Δt. In this equation, v represents average velocity and Δt represents the time intercal. if the average velocity of an object is the same at all time intervals, the object is described as moving at constant, or uniform, velocity. Constant velocity can be calculated using the equation v=d/t.

Position-Time Graphs
A position-time graph is used to show how position depends on time. If the motion is constant, the data produced a(n) straight line, which means the relationship between time and position is linear.

The Slope of a Position-Time Graph
On a position-time graph, the displacement is the vertical separation of two points. The time interval is the horizontal separation. the slop of the ratio of the rise to the run. The rise of the line represents displacement. The run of the line represents the time interval. the slope of the line represents the velocity of the object.

Positive and Negative Velocities
Displacements can be positive or negative, but time interval are always positive. Displacements to the right or the reference point are positive. Displacements to the left of the reference point are negative. Speed is the magnitude of velocity. Speed is generally shown as positive, but velocity can be positive or negative.

Instantaneous Velocity
If motion is not constant, the position-time grpah does not produce a(n) straight line. A straight line can be drawn tangent to the curve at any one point. The slope of this line is the instantanrous velocity at that point.

Velocity-Time Graphs
In a velocity-time graph, time is shown on the horizontal axis and velocity is shown on the vertical axis. If velocity is constant, the velocity-time graph produces a(n) straight line that is parallel to the horizontal axis. If velocity is incresing, the line has a(n) positive slope. If velocity is decreasing, the line has a(n) negative slope. The vertical value of any point on the line is the instaneous velocity at that time. The area under the line on a velocity-time graph is equal to the displacement of the object from its orignal position to its position at a given time.

Relativity of Velocity
Measurements of position of velocity depend on the observer's frame of reference. If a person walks slowly toward the back of a moving train, an observer on the train would say that the velocity and displacement are negative. A observer standing on the station platform would say that the walkers velocity and displacement are positive. Howerever, when velocities approach the speed of light, the frame of reference does not matter, and the velocity is the same, This concept is part of Einstein's theory of relativity.

We were also given time to do other worksheets (chapter 4 study guide and section 4.1: properties of vectors)