describing motion kinematics §2.1–2.2. the tortoise and the hare told in words, formulas, and...
TRANSCRIPT
Describing Motion
kinematics
§2.1–2.2
The Tortoise and the Hare
Told in words, formulas, and graphs
Group Work
Describe the Tortoise-and-hare race using a position-time graph.
CPS Question
Who was fastest?
A. The tortoise.
B. The hare.
C. They had the same speed.
D. What do you mean by faster?
Speed
average speed = xt
over entire interval
Rate of changing position
CPS Question
Who had the fastest average speed?
A. The tortoise.
B. The hare.
C. Their average speeds were the same.
D. Over what time interval?
Speed Units
distance
time= m/s
Example Problem
You are working for the summer on the Wyoming Search and Rescue Squad when you get a call of a downed aircraft. The plane took off from Cheyenne at 12:15, flew north 100 miles and then 80 miles in a direction 30° north of west, where it vanished from radar at 1:05.
What was the average speed of the plane?
Speed as Slope
Speed = distance
time
distance
time
= slope of graph!
d
t
Instantaneous speed
finite t
Young and Freedman, Figure 2.7
smaller t limt0
Speed
xt
at one instantinstantaneous speed = limt 0
= dx/dt
CPS Question
Who had the fastest maximum instantaneous speed?
A. The tortoise.
B. The hare.
C. Their instantaneous speeds were the same.
Illustrating Motion
Young and Freedman, Fig. 2.8
x-t plot motion diagram
Can we make a motion diagram of this race?
Group Work
Describe the Tortoise-and-hare race using a velocity-time graph.
Constant-Velocity Motion
• v = x/t = constant throughout process
• x = vt• xf = xi + x = xi + vt
• Can also use this with average v
Speeds and Areassp
eed
timet1 t2 t3
hare
tortoise
area = vt = distance)
t0 t4