Motion
Part 1: Motion and Speed
Speed
Speed is the distance an object
travels per unit of time.
To calculate speed:
Speed = Distance ÷ Time
Distance is in meters (m)
Time is in seconds (s)
Speed is in meters per second (m/s)
Example 1
A snail takes 5.0 s to crawl across the ruler.
Speed
Speed
Speed
==Distance
=0.07
0.014
m ÷m/s
÷5.0
Time
s
Example 2
A car drives 250 m in one minute.
Speed
Speed
Speed
==
Distance
=250
4.17
m ÷m/s
÷60
Time
s
Use the Formula Triangle!
d
s
t
To calculate
speed:
To calculate
time:
To calculate
distance:
s=d/t
t=d/s
d=sxt
Motion
Part 3: Velocity and Acceleration
Review: Speed
Speed is the distance an object travels
in a specific amount of time.
To calculate speed:
Speed = Distance ÷ Time
Distance is in meters (m)
Time is in seconds (s)
Speed is in meters per second (m/s)
Velocity
Sometimes, knowing the speed isn’t enough.
For example, sailors must know the speed
and direction their boat is travelling in.
Velocity is a description of
both speed and direction.
e.g. a sailboat travelling at
20 kph in a SE direction
Velocity
Sometimes, knowing the speed isn’t enough.
For example, sailors must know the speed
and direction their boat is travelling in.
Velocity is an example
of a vector, a quantity
that has both magnitude
and direction.
Acceleration
Objects can speed up, slow down or change direction.
Acceleration measures how much an
object’s speed changes over a certain time.
Acceleration can be:
A change in speed
A change in direction
A change in speed & direction
Acceleration
Acceleration can be positive, negative or zero.
Positive Acceleration
Object speeds up
Negative Acceleration
Object slows down
Zero Acceleration
Constant or no speed
Acceleration
Formula for acceleration:
acceleration = change in velocity
time
a = Vfinal - Vinitial
t
Velocity: meters per seconds (m/s)
Time: seconds (s)
Acceleration: meters per second squared (m/s2)
Example 1
A motorcycle’s velocity at the top of the hill is
11.0 m/s. 4.0 seconds later it reaches the
bottom of the hill with a velocity of 20.0 m/s.
What is the acceleration of the motorcycle?
a = Vfinal - Vinitial
t
a = 20.0 m/s - 11.0 m/s
4.0
a = 9.0 m/s
4.0
a = 2.25 m/s2
Example 2
A speed skater just finished a race. After she crossed
the finish line, she coasted to a complete stop. If her
initial speed was 13.0 m/s and her acceleration was
-2.9 m/s2, how long did it take her to stop?
a = Vfinal - Vinitial
t
- 2.9 m/s2 = 0.0 m/s - 13.0 m/s
t
t (- 2.9) = - 13.0 m/s
t = - 13.0 m/s / - 2.9
t = 4.5 s