# Motion Notes

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14 Νοε 2013 (πριν από 4 χρόνια και 6 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

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