Physics 2011
Chapter 2:
Straight Line Motion
Motion:
• Displacement along a coordinate axis
(movement from point A to B)
• Displacement occurs during some interval
of Time
Describing Motion:
• Average Velocity, Vav: The speed of
displacement as characterized by the ratio
of a change in displacement to its
corresponding change in time
Describing Motion (Cont.)
• Average Acceleration: The “Speed of
Velocity” as characterized by measuring a
change in velocity and its corresponding
change in time
Problem with Average Quantities
• Velocity is different at every point on the
curve
Instantaneous Velocity, V
• Need to have a more accurate description of
velocity
• A description that is valid at a particular point
during the time interval of interest
• If we can write a time based function describing
displacement, x(t), then velocity is just the
derivative of that function.
Instantaneous Acceleration
• Likewise, a more accurate description of
acceleration is useful
• Given an instantaneous velocity as a function of
time, v(t), the instantaneous acceleration is the
first derivative of the velocity function with
respect to time
• By definition then, Acceleration is also the
Second Derivative of the displacement function,
x(t), with respect to time.
General Equations, Integral Form:
• In general then, since velocity is the
derivative of displacement and
acceleration is the derivative of velocity:
• Given an acceleration as some function of
time, a(t):
Constant Acceleration
• If we don’t allow Acceleration to be a time
varying function (For simplicity and also
because there are many examples of
constant acceleration, such as gravity):
Kinematic Diagrams
• Given some kind of Motion, it is possible to
draw curves and graphs of the motion
based on the equations described in the
chapter.
• Such graphs of motion are called
Kinematic (derived from the word Kinetic,
relating to motion) Diagrams
Motorcycle in Motion:
Motorcycle Motion Data:
Kinematic Diagram of Motorcycle
Motion: