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Chapter 2 Motion
2-1. Speed
2-2. Vectors
2-3. Acceleration
2-4. Distance, Time, and
Acceleration
2-5. Free Fall System
2-6. Air Resistance
2-7. First Law of Motion
2-8. Mass
2-9. Second Law of Motion
2-10. Mass and Weight
2-11. Third Law of Motion
2-12. Circular Motion
2-13. Newton's Law of
Gravity
2-14. Artificial Satellites
2-1. Speed
• Definitions:
– Speed
• The rate at which something moves a given distance.
• Faster speeds = greater distances
– General formula for speed:
• Speed = distance / time
• Abbreviations commonly used:
d = distance t = time v = speed
v = d/t
2-1. Speed
Velocity
miles
 d   100miles 
v 
 40mph
  40
hour
 t   2.5hours 
Distance
 
d  v  t  30 miles

6
hours  180miles
hour
Time
miles
 d   100miles 
t  
 2.5hours
  2.5
miles / hour
 v   40miles / hour 
2-1. Speed
Average speed is the total
distance traveled by an
object divided by the
time taken to travel that
distance.
Instantaneous speed is
an object's speed at a
given instant of time.
2-2. Vectors
Velocity is a vector quantity that includes both speed and
direction.
2-3. Acceleration
Acceleration of an object is the rate of change of its
velocity and is a vector quantity. For straight-line motion,
average acceleration is the rate of change of speed:
change in speed
Accelerati on 
time interval
vf  vi
a
t
2-3. Acceleration
3 Types of Acceleartion
Speeding Up
Slowing Down
Turning
2- 4. Distance, Time and
Acceleration
Vavg =
(V1 + V2)
(20mph + 60mph)
2
2
= 40mph
d = vavg t
30mph 2hr = 60miles
d = ½at2
½ 10m/s/s 52 = 125m
2-5. Free Fall
The acceleration of
gravity (g) for objects
in free fall at the
earth's surface is 9.8
m/s2.
Galileo found that all
things fall at the same
rate.
2-5. Free Fall
The rate of falling
increases by 9.8 m/s
every second.
Height = ½ gt2
For example:
½ (9.8 )12 = 4.9 m
½(9.8)22 = 19.6 m
½ (9.8)32 = 44.1 m
½ (9.8)42 = 78.4 m
2-5. Free Fall
A ball thrown
horizontally
will fall at the
same rate as a
ball dropped
directly.
2-5. Free Fall
A ball thrown into the
air will slow down, stop,
and then begin to fall
with the acceleration
due to gravity. When it
passes the thrower, it
will be traveling at the
same rate at which it
was thrown.
2-5. Free Fall
An object thrown upward at an angle to
the ground follows a curved path called
a parabola.
2-6. Air Resistance
• In air…
– A stone falls faster
than a feather
• Air resistance
affects stone less
• In a vacuum
– A stone and a
feather will fall at
the same speed.
2-6. Air Resistance
• Free Fall
– A person in free
fall reaches a
terminal
velocity of
around 54 m/s
– With a
parachute,
terminal velocity
is only 6.3 m/s
• Allows a safe
landing
2-6. Air Resistance
• Ideal angle for a projectile
– In a vacuum, maximum distance is at an angle of 45o
– With air resistance (real world), angle is less
• Baseball will go furthest hit at an angle of around 40o