Motion• Chapter 1 pp. 12-29
Speed• a measure of how fast something is
moving.
• Equation-
Speed = distance
time
You have to
MEMORIZE
this one!
Units for
speed• mi/h (mph)
• km/h or
• m/s
Use this to
remember the
equation!
• ( / is read per and means divided by)
1.) What is the speed of a car
that has gone 200 km in 4 hrs.?
Answer200km
4 hr
=
50 km/hr
Velocity- describes the speed and direction of
something
• You can change velocity
without changing speed
if you turn a corner.
• If you travel at 10mph
on Lombard street your
speed stays the same.
2.) Does velocity change?
Answer: Yes, several times
Velocity vector• a pictorial representation of velocity
• An arrow that shows the direction of travel
• Length of the arrow shows the speed of
object
Vectors can also represent
other quantities like force
• Shows the direction of the force.
• Length of the arrow = magnitude of the
force
Adding vectors
A
• Vectors that add together
– Component Vectors
(arrows A & B)
• The sum of component
vectors is called a
resultant ( arrow C)
B
Add vectors by lining them up
“tip to tail”
End up with a parallelogram
C
• You cannot add velocity
vectors with force vectors
or acceleration vectors
A
B
Acceleration- the rate of change in velocity
• Acceleration = change of velocity
time interval
Units for
Acceleration• km/hr2
Reads kilometers per hour per hour
Each hour the speed changes so many kilometers per hour
• m/s2
Reads meters per second per second
Each second the speed changes so many meters per second
• km/h/s
Reads kilometers per hour per second
Each second the speed changes so many kilometers per
hour
3.) A car can go from 0 km/h to 90
km/h in 10 s. What is its
acceleration?
Answer90 km/h – 0 km/h = 9 km/h/s
10 s
These units are the hardest to
understand!
4.) What do these units mean?
This answer means that each second
the car is speeding up 9 km/h
Free Fall (Vertical Velocity)• an object falling free of all restraints
• v = gt
– v- velocity
– g- acceleration of gravity
» 9.8 m/s2 on earth
» during each second of fall the
object gains 9.8 m/s in velocity
– t- time
Calculating Vertical Distance• Freely falling objects only
• Equation- d = ½ gt2
– d = distance traveled
» Units- meters
– g = acceleration due to gravity
» Units- m/s2
– t = time of fall
» Units- seconds
5.) A person jumps off a cliff
and has been falling for 1.3 sec.,
how far did they fall?
Answer:
• d = ½ gt2
• d = ½ x (9.8) x (1.3)2
• d = 4.9 x 1.69
• d = 8.28 meters
6.) Why are the units meters?
The units on 9.8 are m/s2.
Done!!