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Motion
Speed, Velocity, Acceleration &
Forces
Frame of Reference
Object or point from
which motion is
determined
What is Motion?
Motion: A change in position of an object
compared to a reference point
Motion involves all of the following:
What is motion?
• If you are standing in one place, and your friend
walks by you, are you moving relative to your
friend?
– Is your friend moving relative to you?
– Is either of you moving relative to the
earth?
Answer:
• You are moving relative to your
friend, and your friend is moving
relative to you!
• You (the Joker) are not moving
relative to the earth, but your friend is.
You are both moving relative to the
sun!
What is motion?
• If you and your friend are walking down the hall
together at the same speed, in the same direction,
are you moving relative to your friend?
– Is your friend moving relative
to you?
– Are either of you moving
relative to the earth?
Answer:
• You are NOT moving relative to your
friend, and your friend is NOT
moving relative to you. You both are
moving relative to the earth.
What is Motion?
Speed
The rate of change in position
Speed = distance ÷ time or
= distance
time
Speed
Example: A car travels 300km in 6
hours. What is the speed of the car?
Answer:
•Speed = distance ÷ time
•Speed = 300km ÷ 6 hours
•Speed = 50km/hr
More practice
•1. How far can a plane travel if it
flies 800km/hr for 9 hours?
•2. How long does it take a ship to
go 500 km if it travels at a speed of
50km/hr?
Answers
1. 7200km/hr
2. 10 hours
What is Motion?
Velocity
Speed plus direction
Example: 50 km/hour north
Velocity
•Speed in a given direction.
•What is the velocity of a boat that
travels from Lancaster to
Baltimore(10 miles) in 15 minutes?
Answer
•Speed = distance ÷ time
•Speed = 10 miles ÷ 15 minutes
•Speed = 0.67 mi/min
•Velocity = 0.67 mi/min NW
Acceleration
•Change in velocity
– Can be change in speed or
direction
Acceleration
The rate of change in velocity
Positive acceleration = speeding up
Negative acceleration = slowing down (decelerate)
Acceleration = Vfinal – Vinitial
Time
or
= ∆Velocity
Time
Acceleration problem
• A roller coaster’s
velocity at the top
of a hill is 10m/s.
Two seconds later
it reaches the
bottom of the hill
with a velocity of
26m/s. What is
the acceleration of
the roller coaster?
ANSWER:
a = 26m/s – 10m/s
2s
a = 16m/s
2s
a = 8m/s/s or 8m/s2
What is a Force?
FORCE = Any push or pull which
causes something to move or change
its speed or direction
What is a Force?
Forces can be BALANCED or UNBALANCED
Balanced forces are equal in size and
opposite in direction
UNbalanced forces are not equal in
size and/or opposite in direction. If
the forces on an object are
UNBALANCED, we say a NET force
results.
Determine the NET FORCE: