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Physics Unit 2
1-D and 2-D Motion
Topics:
What is Linear Motion? Vector vs. Scalar Quantities Distance vs. Displacement (Comparison) Speed vs. Velocity (Comparison) Velocity: Constant, Average, Instantaneous Acceleration
Linear Motion
Motion in one direction
Example: the motion of a Marta train- the train moves either forward or backward along the track
SCALAR
PHYSICAL QUANTITYPHYSICAL QUANTITY
Can be completely specified by its magnitude with appropriate units.•It has no direction.Ex) Distance, time, speed, mass, etc.
PHYSICAL QUANTITY
VECTOR
•Has a magnitude, a unit and a direction•e.g displacement, velocity, acceleration, force.
Demonstrating a Vector
The direction of the arrow indicates the direction of the vector quantity.
The length of the arrow indicates the magnitude of the vector quantity.
ATail Head
ADDING VECTORS -ONE DIMENSIONAL
Vectors are added by placing the tail of one vector at the head of the other vector.
A third vector (C) is drawn by placing the tail of one vector at the head of the other.
A B
C
EXAMPLES
200m 100 m
300 m-resultant
50 m30 m
20 m-resultant
Distance
How far an object actually moves
Displacement•Displacement does not always equal distance traveled•Displacement can be positive or negative
Displacement
Displacement is ZERO
Distance vs. Displacement
Displacement- a change in position
d = df- di
final position - initial position
Displacement Questions1. Amy runs 2 blocks south, then turns
around and runs 3 miles north.
2. Jermaine runs exactly 2 laps around a 400 meter track.
3. Ray runs 30 feet north, 30 feet west, and then 30 feet south.
4. Jamison turns around 5 times.
5. David walks 3 km north, then turns and walks 4 km east.
Speed and Velocity
SpeedSpeed is a rate
Speed is a rate of the distance traveled in a unit of time
Speed
Speed is a measure of how fast something is moving
Speed is a SCALAR quantity- it only requires a magnitude
Calculating Speed
Speed =
Distance traveled
Time
What is the fastest land animal?
The cheetah can travel at speeds up to 100 km/h!!
VelocityThe terms speed and velocity
are used interchangeably
Velocity is speed in a given direction
Velocity VECTOR quantity- it must have both
magnitude and direction– magnitude is a number – direction: north, south, east, west, etc.
Units of Speed and Velocity
Units of distance /unit of time
Meters/sec, miles/hour, kilometers/hour, nanometers/sec,
Velocity Graphs (position vs. time)
A
B
A
CB
D
Constant velocity
Occurs when the average velocity is the same for all time intervals
Also called uniform velocity
Constant Velocity Graph
The velocity is equal to the slope of a distance versus time graph
Average Velocity Used to describe an objects motion when
the velocity is changing, i.e. speed up, slow down, stop, start, etc.
Average velocity will equal the magnitude of an object moving with a constant velocity.
Calculating Average Velocity
Total distance (displacement)/total time
slope of line drawn from start to stopping point on a distance time graph.
Average Velocity
DISPLACEMENT divided by TIME
vavg =
average velocity = change in position = displacement
change in time time interval
if
if
tt
dd
t
d
Instantaneous Velocity The velocity of an
object AT a particular INSTANCE or moment.
Instantaneous Velocity
Determined by drawing a tangent line to the curve and determining the slope of the line.
Example
During her first track meet, Andrea runs with an average velocity of 6.02 m/s to the east. What distance does Andrea cover in 137 s?
Given:
v = 6.02 m/s
t = 137 s
d = ?
t
dV=
s
d
s
m
13702.6
md 825
Example
Last weekend I traveled from Lawrenceville to Dillard (100 km). If I drove 50 km/h for the first 50 km and 100 km/h for the second 50 km, what was my average velocity?
Acceleration
Acceleration is the rate of change in velocity
Acceleration
Acceleration is shown by a curved graph when position (distance) versus time is plotted.