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.