Transcript What is Motion?

Motion
and
Forces
Motion and Force
A. Motion
1. Motion is a change in position
2. Reference points are necessary
Motion is not absolute, it depends on the observer. For
example, if Jack and Jill are sitting in a bus, 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, they
see one another 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, still sees Jill as going 0mph.
What they observe seems to depend on their
reference point.
Reference point or frame of reference is the
background or object that appears to stay in place
when compared to an object being observed 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?
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 or mph), feet per sec (ft/s)
While on vacation, Lisa
traveled a total distance
of 440 miles. Her trip
took 8 hours. What was
her average speed?
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
Speed- distance/time
d
OR
S= d/t
(distance)
S
(speed)
t
(time)
SPEED = DISTANCE/TIME
•The distance between point A and point B is
120m. Jon walked from point A to point B in 15
seconds. What was his speed?
S= 120m/15s
S= 8 m/s
SPEED = DISTANCE/TIME
 Next, Jon walked from point B to point C in 55s.
Jon What was his speed?
S= 300m/55s
S= 5.5 m/s
SPEED = DISTANCE/TIME
•A plane flies 2000 kilometers in 4 hours.
What is the speed of the plane
S= 2000km/4hr
S= 500
km/hr
S= d/t
t= d/S
Frank drove a distance of 150 miles at
60mph. How long did it take him to
Drive the 150 miles?
150mph/60mph=
2.5 hrs
Velocity
Velocity is a measure of both an object’s
speed AND its direction.
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
Acceleration is the rate at which
velocity changes. SO…..if an object
speeds up, slows down or changes
direction, it has ACCELERATED.
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 CENTRIPETAL MOTION.
This means that the direction is constantly
changing.
Graph 2
Graph 1
Graph 3
Graph 1:
Accelerating- the speed at
each plot point on the graph is
different and gaining speed.
Graph 3:
At rest- at each plot point, the
object remains at the same
distance meaning no motion is
occurring.
Graph 2:
Constant speed- the speed at each
plot point is the same which means
speed is constant, not accelerating.
Graph 1
Graph 2
Graph 3
Average Speed = Total distance traveled
divided by Total time of the trip
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.
LET’S
PRACTICE
1. Consider a car moving with a constant velocity of
10m/s North 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
300
200
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9
7
5
3
0
1
DISTANCE (M)
CAR 1 SPEED GRAPH
TIME (SECONDS)
Drag Car 1 traveled 240m in 12 sec. Its average speed was 20m/s.
I know it traveled at a constant speed because of the diagonal line
on the graph and the fact that the speed was the same at every point
along the graph.
200
150
100
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5
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0
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DISTANCE (M)
CAR 2 SPEED
TIME (SECONDS)
Drag Car 2 traveled 150m in 12 sec. Its average speed was
12.5m/s. I know the car accelerated for the first 9 sections of the
race and then came to an abrupt stop at 10 seconds and remained
stopped for the remainder of the race.
150
100
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5
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DISTANCE (M)
CAR 3 SPEED
TIME (SECONDS)
Drag Car 3 traveled 112m in 12 sec. Its average speed was 9.3m/s.
This car accelerated throughout the entire race going faster at the
beginning but very slowly at the end.
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300
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0
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DISTANCE (M)
CAR 4 SPEED
TIME (SECONDS)
Drag Car 4 traveled 315m in 12 secs. Its average speed was 26.3m/s.
Car 4 accelerated for the first two seconds and then came to an abrupt
stop. It stayed still for 3 seconds. It started moving again and
accelerated very rapidly until the end of the race.
WHAT IS A FORCE?
A force is simply a push or a pull.
THERE IS A BIG
RELATIONSHIP BETWEEN
FORCE AND MOTION
WITHOUT A FORCE THERE
WOULD BE NO MOTION.
Examples of forces acting on
objects would be:
A flag being blown by the force
of the wind.
A jet engine propelling an
airplane forward.
Iron being pulled toward a
magnet.
Examples of forces acting on
objects would be:
Opening and closing a door.
A space shuttle lifting off
What type of force would these
objects need to move?
Sports
equipment
kites
wagons
sleds
Forces
What types of forces can you think of?
How is the object affected by those
forces?
FORCES ALWAYS
OCCUR IN PAIRS
Forces can:
1) give an object the
energy to move
2) cause object to stop moving
3) Change objects direction.
Net Force
• Total amount of force acting on an object.
• Will also determine motion and direction of motion.
HOW DOES FORCE CAUSE
MOTION?
Motion is a result of UNBALANCED
FORCES.
UNBALANCED FORCE is when the
net force on an object is greater than 0.
HOW DO UNBALANCED FORCES
CAUSE MOVEMENT?
REMEMBER: Forces always
come in pairs.
2 Unbalanced forces acting in the same
direction get added together and cause
motion.
EXAMPLES OF
UNBALANCED FORCES
PUSHING A
SHOPPING
CART
SKIING
DOWNHILL
WHAT IS A BALANCED
FORCE?
Balanced Forces cause no motion.
= when the net force on an object
is zero.
The paired forces occur in
opposite directions and are of
equal force.
EXAMPLES OF BALANCE
FORCE
There is an
equal amount of
people playing
tug of war.
WHICH PICTURES SHOW BALANCED FORCE?
WHICH PICTURES SHOW UNBALANCED FORCE?
If you chose answer F, you are correct!
Less force = Less distance traveled
FRICTION : FORCE THAT OPPOSES MOTION
Friction - The force that opposes motion between
two surfaces.
 Friction occurs because all surfaces are
covered with microscopic hills and valleys,
which make the surface rough.
When surfaces touch, the hills and valleys stick
to each other and this causes friction even if the
surfaces look smooth.
If you chose C, you are correct!
The open umbrella has more surface area/ more
air resistance and will take longer to drop.