Transcript FORCE AND MOTION

FORCE AND
MOTION
MEASURING MOTION
BELLRINGERS
1. What two things must you know to determine speed? What
is the formula for speed?
2. Alex rode his bicycle 60 kilometers in 4 hours. How fast was
he going? Matt rode 90 meters in 6 minutes. How fast was he
going?
3. Explain why is would be important to know a tornado’s
velocity and not just its speed.
4. Read pg. 7 in your packet and complete the questions on
the back of the page.
5. Put the finishing touches on your Car Distance/Time Graphs.
WHAT IS MOTION?
Motion is a change in an objects position
over time when compared with a reference
point.
Reference point or frame of reference is the
background or object that is used as comparison
to the object in motion.
Most common reference point is the Earth’s
surface.
Other reference points are buildings, trees,
mountains etc.
What reference point
do the balloonists
use?
Motion is not absolute, it depends on the observer. For
example, if Jack and Jill are sitting in a room, Jack sees Jill
at rest and Jill sees Jack at rest. BUT, if we zoom out, we
see that Jack and Jill are sitting on a bus moving at a
constant speed of 25mph. From the reference INSIDE the
bus, Jack sees Jill at rest and Jill sees Jack at rest.
Jill’s mother, waiting for the bus, sees Jill’s bus go
by at 25mph. She sees Jill traveling 25mph. Jack
on the other hand, sees Jill as going 0mph. What
they observe seems to depend on their reference
point.
While riding the bus, Jill begins throwing
cookies to Jack. Jill can throw cookies at a
speed of 30 mph. From their reference
point, Jack and Jill both see the cookies
going 30mph.
As Jill’s mom observes the cookie tossing from
where she is standing on the side of the road, she
sees the cookies going 30mph on a bus moving
25mph in the same direction. SO, she observes the
cookies going 55mph!!!!!!
As Jill continues to throw 30mph cookies at Jack,
the bus drives by Jack’s mom on a bicycle. She is
riding 10mph in the same direction as the bus is
traveling 25mph. From her point of reference,
Jack seems to only be going 15mph (25mph –
10mph) and she see the tossed cookies going
45mph (15mph + 30mph).
As the cookie tossing between Jack and Jill
continues, a car drives by going 40mph in the
other direction. The observer in the car sees Jack
going 65mph (40mph + 25mph). The observer
then notices the flying cookies to be traveling a
whopping 95mph!!!!!! (40mph + 25mph +
30mph).
SO WHAT IS SPEED?
Speed is the rate at which an object
moves. This is determined by the distance
traveled and the time it takes to travel.
SO…
SPEED = DISTANCE / TIME
UNITS FOR SPEED: meters per sec (m/s)
miles per hour (mi/hr), feet per sec (ft/s)
AVERAGE SPEED VS
CONSTANT SPEED
Average Speed = Total distance traveled
divided by Total time of the trip
AVERAGE SPEED VS
CONSTANT SPEED
Constant speed – speed that does not change.
Every plot point on the graph has the same speed
When you see a graph like this, you will know that
the object is traveling at a constant speed. Double
check yourself by calculating the speed at each point.
SOLVE THIS PROBLEM
While on vacation, Lisa
traveled a total distance
of 440 miles. Her trip
took 8 hours. What was
her average speed?
SOLVE THIS PROBLEM
While on vacation, Lisa traveled a total
distance of 440 miles. Her trip took 8
hours. What was her average speed?
SPEED = DISTANCE/TIME OR SPEED = D/T
DISTANCE – 440 MILES
TIME – 8 HRS
SPEED – 55 MILES PER HOUR
Which graph shows constant
speed?
VELOCITY
Velocity is the speed of an object in a
specific direction.
Speed and Velocity do not mean the
same thing
Velocity changes as speed or direction
changes.
Which of the following are examples
of velocity?
1. 25 m/s forward X
2. 1/500 km/h
X
3. 55 m/h south
4. 10, 000 m/s
BELLRINGERS
1. What two things must you know to determine speed? What
is the formula for speed?
2. Alex rode his bicycle 60 kilometers in 4 hours. How fast was
he going? Matt rode 90 meters in 6 minutes. How fast was he
going?
3. Explain why is would be important to know a tornado’s
velocity and not just its speed.
4. Read pg. 7 in your packet and complete the questions on
the back of the page.
5. Put the finishing touches on your Car Distance/Time Graphs.
COMBINING VELOCITIES
2 velocities in the SAME DIRECTION – subtract the
smaller velocity from the larger velocity to find the
resultant velocity.
2 velocities in DIFFERENT DIRECTIONS – add them
together to find the resultant velocity.
Acceleration is the rate at which
velocity changes. SO…..if an object
speeds up, slows down or changes
direction, it has ACCELERATED.
ACCELERATION – CHANGES IF
SPEED, DIRECTION OR BOTH
CHANGES
TYPES OF ACCELERATION
Positive Acceleration – occurs when
velocity increases.
Negative Acceleration – occurs when
velocity decreases.
This is also called deceleration.
SO… what about this? What
type of motion does it have? Is
the object accelerating?
Is the object changing speed?
NO!
Is the object changing direction?
YES!!!! An object traveling in a
circle is constantly changing
direction. SO… is the object
accelerating?
Objects that are continuously accelerating
is called CIRCULAR MOTION. This
means that the direction is constantly
changing.
LET’S
PRACTICE
1. Consider a car moving with a constant velocity of
10m/s for 5 seconds. Look at the data table and
draw a graph of the results into your notes.
Does your graph look like this? What kind of
graph is this? What is the speed?
The object is traveling at a
constant speed of 10 m/s
for 5 seconds.
2. Consider a car moving with a constant velocity
of 5 m/s for 5 seconds, stopping abruptly, and
then remaining at rest for 5 seconds. Graph the
information into your notes.
Does your graph look like this?
Whenever there
is a flatline, this
means motion
has stopped.
3. Look at the picture and graph the information.
Does your graph look like this? What is the
speed?
Graphs that look
like this always
show …….
ACCELERATION
Speed is NOT the same at
every point along the line
Look at the two cars below. The blue car starts “ahead” of
the red car (which actually starts off the screen). Since the
red car is moving faster, it eventually catches up with and
passes the blue car. Since the red car passes the blue car,
there is an instant where they occupy the same position. At
how many seconds and at what distance does this occur?
What speed are the cars traveling at this position?
Which car or cars are accelerating?
Only the blue and the green cars are
accelerating. But why not the red?
The red car is traveling at a constant
speed. Since it is constant nothing is
changing!!!!!
Which car is experiencing the greatest
acceleration?
IT MUST BE THE BLUE CAR
BECAUSE IT OVERTAKES
ALL THE OTHERS
Look at the distance/time graph. Each one of
the three lines corresponds to the motion of
one of the three cars. Match the appropriate
line to the particular color of car.
LET’S
PRACTICE
THINK ABOUT RIDES IN AN AMUSEMENT
PARK
1. WHICH RIDES HAVE CONSTANT
SPEED?
2. WHICH RIDES HAVE CIRCULAR
MOTION?
3. WHICH RIDES ACCELERATE?