Bellringer
EXPLAIN IN COMPLETE SENTENCES WHAT IS
KINETIC ENERGY
Velocity vs Time Graphs
slope = velocity
d
t
slope = acceleration
v
area = distance
t
(Page 61 in Workbook)
If the graph is a horizontal line,
there is no change in velocity,
therefore there is no acceleration
(the slope is 0).
If the acceleration is positive
then the slope is positive (the
line moves upward to the right).
If the acceleration is negative, then
the slope is negative (the line moves
downward to the right).).
Calculating acceleration from a velocity-time graph
The slope of a
velocity-time graph
is the acceleration.
Calculating the distance on velocity-time graph.
The area under the velocity-time graph
gives the displacement of the object for
the specified time interval.
The velocity-time graph for
acceleration is a straight line.
constant
An object is moving in the positive direction if the line is
located in the positive region of the graph (whether it is
sloping up or sloping down).
An object is moving in the negative direction if the line is
located in the negative region of the graph (whether it is
sloping up or sloping down).
If a line crosses over the x-axis from the positive region
to the negative region of the graph (or vice versa), then
the object has changed directions.
The Average Velocity for each section of a velocity time graph
is found by Adding the initial and final velocities with each
section and dividing the sum by 2.
Avg vel = (Vi + Vf) / 2
Velocity Time Graphs
• How can you tell if the object is
accelerating or decelerating?
– Accelerating (speeding up) – when the magnitude
of the velocity is increasing
– Decelerating (slowing down) – when the magnitude
of the velocity is decreasing
The object moves in the + direction at a constant
speed - zero acceleration (interval A).
The object then continues in the + direction while
slowing down with a negative acceleration (interval B).
Finally, the object moves at a constant speed in the +
direction, slower than before (interval C).
The object moves in the + direction while slowing down; this
involves a negative acceleration (interval A).
It then remains at rest (interval B).
The object then moves in the - direction while speeding up;
this also involves a negative acceleration (interval C).
The object moves in the + direction with a constant velocity
and zero acceleration (interval A).
The object then slows down while moving in the + direction
(i.e., it has a negative acceleration) until it finally reaches a
0 velocity (stops) (interval B).
Then the object moves in the - direction while speeding up;
this corresponds to a - acceleration (interval C).
Homework
DESCRIBE YOUR MOTION USING THE CONCEPTS
WE LEARNED TODAY