Motion in one dimension
 motion is “relative”, or depends on
your frame of reference
 rate is a quantity divided by time
Speed: how fast something is
moving
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“/” means per,
“” means change in
Speed = distance / time
average speed = total distance covered /
time interval
Questions
• If the odometer reads
zero at the beginning
of a trip and 35 km a
half hour later, what is
the average speed?
• Would it be possible to
attain this average
speed and never
exceed 70 km/h on the
speedometer?
• If a cheetah can
maintain a constant
speed of 25 m/s, it will
cover 25 meters every
second. At this rate,
how far will it travel
in 10 seconds? In 1
minute?
Velocity = speed with direction
• distinction between speed and velocity is
direction
• you can have a constant speed and have a
changing velocity
• average velocity = displacement / time
elapsed
– ¯v = = x2 - x1 / (t2 - t1) = x / t
• instantaneous velocity = average velocity
over an infinitesimally short time
Questions:
• If an airplane travels
500 km due north in 1
h, what is its velocity?
• 250 km due north in
1/2 h?
• 125 km north in 1/4 h?
• What are three
“velocity changers” on
a car?
Acceleration = CHANGE in
velocity / change in time
• it can be felt!! Whenever you’re in an
automobile
• it can be positive - a car accelerates from 0
- 60 mph in 60 seconds
– 60 mph / 60 sec = 1 mi / hr / sec
• it can be negative - a car moving at 30 mph
comes to a stop in 10 seconds
– -30 mph / 10 sec = -3mi / hr / sec
Question:
• What is the
acceleration of a car
that goes from 0 to
100 km/h in 10 s?
Question
• What is the
acceleration of a
mechanical part that
moves from 0 - 10 m/s
in a time of 1 s?
Free Fall: How Fast
• Does an object dropped from your hand
accelerate?
• What does it mean to say it accelerated 10
m/s2?
• ASSUMPTION: Air resistance is
negligible!
• Freely falling objects are affected only by
gravity, “g”
• the acceleration of an object falling is about
10 meters per second squared
Question:
• If an object is dropped from rest from the
top of a cliff, how fast will it be going at the
end of 1 second?
• What is the speed at the end of 2 seconds?
• What is the speed at the end of 10 seconds?
Free Fall: How Fast
• acceleration = change in speed / time
interval
• instantaneous speed = acceleration x
elapsed time
• v = gt
Question
• If you threw a ball straight up with an initial
velocity of 30 m/s, how long would it take
for it to reach its peak height?
• (HINT: Draw a picture!!)