Transcript Section 1 Describing Motion A. Motion

Motion
Describing Motion
Motion – when an object changes
its position relative to a reference
point
Distance – how far an object
moves
Displacement – how far an object
moves in reference to the starting
point
Rates
Any change over time
Examples:
$7.50/hr
Rpm (rotations per minute)
Accidents/month
Miles/hr
m/s
Speed / Velocity
Distance traveled per unit of time
Speed = distance / time
Speed describes the rate of motion
Velocity includes the rate of motion and
direction
Speed
Speed that doesn’t change over time is
constant speed
Most speeds are non constant average speed
Why can’t you run at a constant rate?
Average and Instantaneous Speed
Average speed is taken when speed is variable.
Average speed = total distance / total time
Instantaneous Speed = speed at any given
point in time
Distance vs. Time Graphs
Visual representation of an
object’s motion
Plot distance on the vertical
axis (y-axis)
Plot time on the horizontal
axis (x-axis)
Which is the
independent variable?
Which is the dependent
variable?
What does this graph
represent?
AGENDA 1/19/11
You will need your textbook for the assignment
today
Access Chapter 2 Notes from my public folder
Acceleration Discussion
Ch. 2 Handout
Acceleration
Acceleration is a change in the motion of an object.
Positive acceleration – velocity is increasing
Negative acceleration – velocity is decreasing
Changing an object’s direction is also accelerating
YOU CAN FEEL ACCELERATION
Calculating Acceleration
Acceleration = change in velocity / time
A = ΔV / t
(VF – VI)
___________
t
Acceleration
Unit of acceleration is m/s2.
A velocity vs. time graph
Which is the dependent variable?
Which is the independent variable?
(+) acceleration has a
positive slope
(-) acceleration has a
negative slope
Where is acceleration experienced at an
Amusement Park?
Newton’s Laws of Motion
1st Law- “an object in constant motion remains in
constant motion until acted upon by an outside
force.”
The law of inertia
2nd Law- F = ma
3rd Law- “for every action there is an equal and
opposite reaction.”
Forces
Force- a push or a pull exerted from one object to
another
Balanced Forces- forces acting on an object are
all equal and in opposite directions
Unbalanced Forces- the magnitude and
direction of the forces do not cancel one
another out
Causes motion