Transcript Motion and Speed

Motion and Speed
Answer the following questions on
your notes:
• Explain in detail how you could tell that the
object was moving.
• Describe the motion of the object using
the things around it.
• Define motion without using any form of
the term “move” (This means you can not
use the words like moved, moving, etc.).
• Are there any situations you can think of
where detecting motion could be difficult?
Explain.
Motion
Change in position in relation to a reference point.
Reference Point
A non-moving object from which motion is measured
Reference point
Motion
Problem:
You are a passenger in a car
stopped at a stop sign. Out of the
corner of your eye, you notice a tree
on the side of the road begin to
move forward.
You have mistakenly set yourself as
the reference point.
Newton’s First Law
Newton’s First Law of Motion
An object at rest will remain
at rest and an object in
motion will continue moving
at a constant velocity
unless acted upon by a net
force.
Speed
• Rate of motion
• Distance traveled by an object divided by
the time interval during which the motion
occurred (distance traveled per unit of time)
distance
speed 
time
Average Speed
• Most of the time objects do not travel at a constant
speed
– You probably do not walk at one constant speed on
the way to class
• This is why when we talk about how fast an object is
moving we are usually talking about its average speed.
• If we are talking about an object’s speed at a particular
instant in time, you would be describing the
instantaneous speed of the object.
total distance
average speed 
total time
Let’s practice….
• An athlete swims a distance from one end
of a 50 m pool to the other end in a time of
25 seconds. What is the athlete’s average
speed?
• Average speed = total distance
total time
Average speed = 50m
25 s
Average speed = 2 m/s
Problem:
A storm is 10 km away and is
moving at a speed of 60 km/h.
Should you be worried?
It depends on the
storm’s direction!
Velocity
• Speed in a given direction
– Velocity must include speed of an object and
direction!
– Example: If you were to give the velocity of
an airplane and you said it was 600 km/h, you
would be incorrect. Why?
– You must give a direction. You could say the
plane’s velocity is 600 km/h south.
Velocity
• An object’s velocity changes if either it’s
speed or direction changes.
• In order for velocity to remain constant, the
object must travel on a straight line in the
same direction.
Acceleration
• The rate at which velocity changes
• Acceleration occurs when an object
changes speed, direction, or both
• An increase in velocity is called positive
acceleration.
• A decrease in velocity is called negative
acceleration or deceleration.