Define the term motion. Give an example of something in motion. How do we know an object is in...
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Transcript of Define the term motion. Give an example of something in motion. How do we know an object is in...
S-9
Define the term motion. Give an example of something in
motion. How do we know an object is in
motion? How do we know if we are in motion
even if our eyes are closed?
Chapter 2Motion
SPS8 Students will determine relationships among force, mass, and motion.a. Calculate velocity and acceleration.
11.1 Distance and Displacement
What is needed to describe motion completely?How are distance and displacement different?How do you add displacements?
11.1 Distance and DisplacementI can determine an appropriate frame of reference and decide if an object is moving
How do we know an object is moving?
Frame of reference Motion is always relative (compared to) something That something is called the Frame of Reference for us usually the earth)
11.1 Distance and DisplacementI can determine an appropriate frame of reference and decide if an object is moving
How do we know an object is moving? Frame of reference
We choose a frame that makes sense. Using the ground as a frame, the ball is moving forward Using the truck as a frame of reference, the ball goes up then back down
11.1 Distance and DisplacementI can explain the difference between distance and displacement
Distance – the length of a path between two points
Displacement – straight line distance (and direction) between the start and end
Example: Travel 3.5 miles south
PHET Vector
Addition
11.1 Distance and DisplacementI can add one dimensional vectors for displacement, velocity, and acceleration
Adding Displacements (vector addition)
Vector – has number value and direction
If the vectors aren’t in a straight line, then we have to use trigonometry to add the vectors
11.2 Speed and Velocity
How are instantaneous speed and average speed different?How can you find the speed from a distance-time graph?How are speed and velocity different?How do velocities add?
SR-71 BlackbirdSpeed: 2070 mphor 920 m/s
11.2 Speed and VelocityI can calculate the average speed for a moving object.
Speed – ratio of distance to time Measured in meters per second (m/s) Average Speed
Example: A car travels 25 km in 0.2 hours, then 45 km in 0.3 hours. What is the average speed?
Total distance and then total distance
TimeTotal
ceDisTotaledAverageSpe
.
tan.t
dv
tv
4525
t
kmv
70
3.02.0
70
kmv
hr
kmv
5.0
70 hr
kmv 140
11.2 Speed and VelocityI can calculate the average speed for a moving object.
Practice: A person jog 400 meters in 192 seconds, then 200 meters in 132 seconds, and finally 100 meters in 96 seconds. What is the joggers speed?
t
dv
96132192
100200400
vs
mv
420
700 s
mv 67.1
11.2 Speed and VelocityI can calculate the average speed for a moving object.
Practice: A train travels 190 kilometers in 3.0 hours, and then 120 kilometers in 2.0 hours. What is its average speed?
t
dv
0.20.3
120190
vhr
kmv
0.5
310 hr
kmv 62
11.2 Speed and VelocityI can calculate the average speed for a moving object.
A speedometer does not measure average speed, it measures instantaneous speed.
11.2 Speed and VelocityI can calculate speed from a distance time graph.
A distance time graph can be used to determine speed.
The slope of the graph (distance divided by time) is average speed
GizmoDistance vs. Time
11.2 Speed and VelocityI can list two ways velocity changes and show these changes by graphs or diagrams.
Velocity – speed in a direction (vector)
Velocity changes with either A change in speed A change in direction
Velocity is added by vector addition (like displacement)
11.3 Acceleration
How are changes in velocity described?How can you calculate acceleration?How does a speed-time graph indicate acceleration?What is instantaneous acceleration?
11.3 AccelerationI can define acceleration.
Acceleration is a change in velocity, so Change in speed▪ Either getting faster▪ Or getting slower
Change in direction▪ Turning
Measured in meters per second squared (m/s2)
11.3 AccelerationI can calculate the acceleration for an object changing speed.
Calculating Acceleration – divide the change in velocity (speed) by the total time
Example: A ball rolls down a ramp, starting from rest. 4 seconds later, it’s velocity is 13 m/s. What is the acceleration of the ball?
First, what is the initial velocity? 0 m/s
timetotal
velocityinchangenAccleratio
.
..
t
va
t
vva if
s
a4
013
sa s
m
4
13 225.3
sma
11.3 AccelerationI can calculate the acceleration for an object changing speed.
Practice Problem 1
A car traveling at 10 m/s slows down to 3 m/s in 20 seconds. What is the acceleration?
t
vva if
sa
20
103
sa s
m
20
7 235.0
sma
11.3 AccelerationI can calculate the acceleration for an object changing speed.
Practice Problem 2
An airplane travels down a runway for 4.0 seconds with an
acceleration of 9.0 m/s2. What is its change in velocity during this time?
t
va
s
vsm
0.40.9 2
vs
sm 0.40.9 2
smv 36
11.3 AccelerationI can determine acceleration from a speed-time graph.
Reading a Speed-Time graph The slope of the graph (rise over run)
is the acceleration Straight upward – positive constant
acceleration Straight downward – negative constant
acceleration (slowing down) Flat – constant speed, no acceleration Curved – changing acceleration
11.4 Free Fall
How does gravity cause acceleration?
Free Fall – when an object is falling under only the influence of gravity
The acceleration due to gravity on the surface of the earth is 9.80 m/s2
So our acceleration equation becomes
Everything else is the same
11.4 Free FallI can calculate using the acceleration due to gravity.
t
vv if
sm
280.9
Problem 1 How fast will a rock dropped from the top of the empire state building be going after 8.0 seconds?
11.4 Free FallI can calculate using the acceleration due to gravity.
t
vv if
sm
280.9
s
v fsm
0.8
080.9 2
s
v fsm
0.880.9 2 fsm vs 0.880.9 2 fs
m v4.78