PH 104 w/DrG Lec4
More about: acceleration
Linear Motion 2/2
PH 104 w/ dr. g
Lec 4
Moving in a straight line: More about acceleration
Acceleration = (Change in velocity) / Time.
y Recall: riding inside car in uniform motion
y (you are in an “inertial frame of reference”)
y Cannot detect difference between moving and at rest
y Feel difference: only with acceleration (feel a force)
y Going from zero velocity to nonzero velocity, v
Free fall is accelerated motion.
y Over time interval t, acceleration a =
y So velocity attained from rest, over time t is
Moving in a straight line: More about acceleration
Acceleration = (Change in velocity) / Time.
y Galileo’s inclined planes: Interactive figure
y All angles: takes SAME time to reach bottom
y Higher angle of incline = higher v (3.0 s) = higher a
Galileo’s inclined planes, continued:
y Incline-plane results: SAME for all MASSES.
y = (9.8 m/s2) times sine of angle
y Extrapolate: For angle = 90 deg, a = 9.8 m/s2
Free-fall: CONSTANT acceleration
y Acceleration of falling (no air friction) =
y Each case: same change in velocity every 0.5 s
y = constant, a
y = graph of velocity vs. time:
Galileo’s Experiments: Results:
Free-fall: CONSTANT,
universal acceleration
y Acceleration of falling (no air friction)
= 9.8 m/s2 = “g”
y (Aristotle: Different masses fall at
different accelerations.)
y Galileo: Tower of Pisa: All objects fall
with same acceleration = g = 9.8 m/s2
regardless of mass
Galileo Galilei (Italian, 1564 – 1642)
• First to prove that all objects fall with
constant acceleration.
• This constant acceleration is the same
for all objects.
y How can this be??? (…later…)
Leaning Tower
of Pisa
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PH 104 w/DrG Lec4
QUESTION 1
QUESTION 2
From the top of a cliff, a ball is released from rest.
Neglect air resistance.
After 10 seconds, its acceleration will be
From the top of a cliff, a ball is released from rest.
Neglect air resistance.
After 10 seconds, its speed will be
(a)1 m/s2
(b)10 m/s2
(c)100 m/s2
(d)Cannot determine; need more info!
(a)1 m/s
(b)10 m/s
(c)100 m/s
(d)Cannot determine; need more info!
Free-fall: CONSTANT acceleration.
QUESTION 3
y Different starting velocities : Interactive figure
a=
( v at time2) - (v at time1)
time2 - time1
y From rest :
y velocity acquired after t is v = g t
y Distance covered = (average v) t = (½v)t
d = (½
(½v)t = (½gt) t =
y Thrown downward: velocity still increases at 9.8 m/s per sec
A ball is thrown straight up with an initial speed of 30
m/s. How high does it go?
(a)30 m
(b)45 m
(c)300 m
(d)Cannot determine; need more info!
y Thrown upward: deceleration, followed by acceleration
y IN EVERY CASE, AT ALL TIMES acceleration = g, down
QUESTION 4
From the top of a cliff, a ball is released from rest.
Neglect air resistance.
After 10 seconds, it will have fallen _______meters.
(a)5 m
(b)50 m
(c)500 m
(d)Cannot determine; need more info!
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