Describing Motion

I love physics, but I hate moving.

Kinematics

· Examine the different ways of relating motion.

· Graph and examine position-time for uniform motion.

Motion can be described in a lots of ways:

Verbal - words to describe position and motion.

Symbolic - equations to relate displacement, time and velocity.

Numerical - data tables to indicate position at an instant in time.

Graphical - graphs giving direct information of position and time.

CONSTANT velocity - NO CHANGE in size OR direction.

Movement shown in the data table is – UNIFORM MOTION –

What is the velocity between 10 and 15 seconds?

v = ΔdΔt

v =

v = 2 m/s [E]v = 10 5

30 - 2015 - 10

PO

SIT

ION

(m

)TIME (s)

10

20

30

40

50

5 10 15 20 2500

Time is plotted on the HORIZONTAL AXIS. Position is plotted on the VERTICAL AXIS.

A STRAIGHT line represents UNIFORM motion.

PO

SIT

ION

(m

)

TIME (s)

10

20

30

40

50

5 10 15 20 2500

P-T graphs tells where an object is at a given time.

The slope of P-T graphs give velocity of the object.

RISE

RUN

Rise:Δd = d2 - d1

= 21 - 7= +14

Run:Δt = t2 - t1

= 11 - 4= +7

v = + 2.0 m/s

y

10

20

30

40

50

5 10 15 20 2500

x

The slope of a line shows the change of one thing compared to another.

Slope =

Slope = xy

run rise

Slope =

Slope = + 2

40 - 1020 - 5

Making a Position -Time graph

· 2 - walker, 7 - timers, 1 - recorder

· timers line up 10 metres apart (70 m total distance)

· all timers start clock when walker begins

· each timer stops clock when runner passes them

· walkers must try to maintain a constant velocity

· the second walker must walk faster than FIRST.

0.010.020.030.040.050.060.070.0 70

635139272290.0

Time (s)Position (m)

0:00 0:09 0:22 0:27 0:39 0:51 1:03 1:10

Pos

ition

(m)

Time (s)

PO

SIT

ION

(m

)

TIME (s)

10

20

30

40

50

5 10 15 20 2500

What is the velocity of the walker?

v =

v = 2 m/s [E]v = 20 10

v = ΔdΔt

50 - 3025 - 15