Motion Notes

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14 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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Motion Notes

Overview

Mechanics


2 parts


Kinematics


Characteristics

of motion


Dynamics


Causes

of motion

Kinematics


Imagine a three legged stool and each
leg is a fundamental parameter of
motion:


Position

(distance/location)


Time


Speed


Kinematics


Position


Position

(linear measure)


Where an object is located at specific point in
time


Units of meters


Can be described in terms of:


Distance

(scalar)


measure from one position to another


Displacement

(vector)


measure from one position to another in a direction


distance

from the start point to the finish point in a
straight line, in a certain
direction

Stop here

Kinematics
-

Speed


Definition


Rate of change of position


Average Speed

(scalar) =
distance traveled


time taken to travel the distance


Velocity

(vector) =
displacement


time taken


When traveling in a straight line, speed and velocity have
the same magnitude.


v
av

= d/t


Units:

meters/second (m/s)


Distance

is to
speed

(both
scalar

quantities)
as
displacement

is to
velocity

(both
vector

quantities).

Example


speed


Usain

“Lightning” Bolt won the World
Track & Field 100m sprint in 9.58
seconds. What was his average speed
in m/s?


Solve:
avg

speed = distance/time


Speed (v) = 100/9.58 = 10.438 m/s

Example
-

segments


A traveler uses a cab to travel east for
1000 m @ 25 m/s then north for 1700 m
@ 10 m/s. How long is the trip?


Solution
: break the trip into segments
and use d = v*t or t = d/v to find the
segment times


then add.


Seg

1: t = 1000/25 = 40 seconds


Seg

2: t = 1700/10 = 170 seconds


Total time = 40 + 170 = 210
seconds.
Stop


http://www.physicsclassroom.com/Class/
1DKin/U1L1c.cfm

see
teachers tab



Kinematics
-

Acceleration


How do you pass a car on I
-
81?


Definition


Rate of change of velocity


a =



tⰠ潲


a = (
v
f



v
0
)/t, where


v
f

= final (ending) velocity


v
0

= initial (starting) velocity


t = time taken for the velocity to change


units
: meters/sec/sec, or meters/sec
2

(m/s
2
)


VECTOR
!


Average speed (alternative formula)


Vav

= (v
0

+
v
f
)/2

Example
-

acceleration


A funny car accelerates from zero to 300
mph (135 m/s) in 5 seconds. What is its
acceleration?


Solve: acceleration = (
v
f



v
o
)/t


a = (135
-

0)/5


a = 27 m/s/s


a = 27 m/s
2


g
-
forces?
STOP


Kinematics


Graphs

(Distance vs Time)


slope

=
velocity or
speed
of the object


Steep

(left) slope =
higher

speed


Zero

slope (flat line)
= object stationary


Slope can be + or


indicating motion
direction

Kinematics


Graphs

(Velocity vs time)


slope is
acceleration


Steep

(left) slope =
higher

accel’n


Zero

slope (flat line) =
zero
accel’n

or the
object is moving at
constant speed


Slope can be + or


indicating speed
direction
STOP

Practice
-

Handouts


H/O Interpretation of Motion Graphs


D
-
T & V
-
T


H/O d
-
t & v
-
t graph worksheet


D
-
T & V
-
T


H/O Position Time


D
-
T & V
-
T