Transcript Example #2 - Sizemore Science

2D Motion
IntervalDist.(m)
IntervalTim e( s)
Freefall Post Lab
Analyzing Data
Interval
Interval
Dist. (cm)
Increase
dist.(cm)
AB
NA
BC
BC-AB
CD
CD-BC
Interval
Time (s)
Average
Vel. (m/s)
Accel.
(m/s2)
NA
Freefall Post Lab
First Graph Questions
1. What’s the shape of the
graph?
2. What does the shape of graph
infer about the motion of the
tape?
3. What does the y-intercept
represent?
4. What does the slope of a line
tangent to the curve
represent?
5. Is the tape moving at point A?
Explain.
6. Which of our basic equations
best fits the graph?
7. What does this acceleration
Freefall Post Lab
Second Graph Questions
8. What’s the shape of the graph?
9. What does the shape of graph
infer about the motion of the
tape?
10. What does the y-intercept
represent?
11. What does the slope of the curve
represent?
12. Is the tape moving at point A?
Explain.
13. Which of our basic equations
best fits the graph?
14. Calculate the acceleration of the
tape.
15. What does this acceleration
represent?
Freefall Post Lab
Define Freefall
Any condition in which the only force
affecting your motion is gravity.
Example #1
A brick is dropped from the roof of a building
under construction. The brick strikes the ground
after 4.85 seconds. What’s the brick’s velocity
just before it reaches the ground?
Example #1
A brick is dropped from the roof of a building
under construction. The brick strikes the ground
after 4.85 seconds. How tall is building?
Example #2
A kangaroo is playing catch with herself by
kicking a ball straight up. How fast does she kick
the ball if the ball comes back to her foot 2.5
seconds later?
Example #2
A kangaroo is playing catch with herself by
kicking a ball straight up. How high did the ball
rise?
Freefall Ball-Terminal Velocity Post Lab
Part 1 Describe the acceleration of ball as it rises,
reaches the top, and falls. Ignore Air Resistance.
FBD’s
Ball as it leaves hand
Ball at top of flight
Ball Falling
Freefall Ball-Terminal Velocity Post Lab
Terminal Velocity-Definition
Factors affecting the force of air resistance
Freefall Ball-Terminal Velocity Post Lab
Part 2
(a)How does the terminal velocity seem to depend on the
mass of the coffee filters (number of coffee filters)?
(b) What is the acceleration of the coffee filters when they
reach terminal velocity?
(c) How can you tell what the terminal velocity of the
coffee filters is from the position versus time graph?
Position vs. time graph for freefalling coffee filters
Freefall Ball-Terminal Velocity Post Lab
Part 2
(d) If we could remove all of the air from the room,
describe the free fall acceleration of a
i. softball
ii. inflated balloon
iii. coffee filter
iv. feather
v. bowling ball
vi. Parachute
Explain your answers.
Example #3
A 0.005 kg coffee filter is dropped from rest from a
height h above the floor. The filter falls for 1 s
before reaching terminal velocity.
What is the filter’s acceleration immediately
(at t = 0 s),and after it is dropped?
Example #3
A 0.005 kg coffee filter is dropped from rest from a
height h above the floor. The filter falls for 1 s
before reaching terminal velocity.
What is the filter’s acceleration when it reaches
terminal velocity?
Example #3
A 0.005 kg coffee filter is dropped from rest from a
height h above the floor. The filter falls for 1 s
before reaching terminal velocity.
What is the magnitude of the air resistance force
while falling at terminal velocity?
FBD at terminal velocity
Projectile Motion Post Lab
Questions
Define projectile:
Any object moving through space above
the surface of the earth acted on only by
earth’s gravity
Define trajectory:
The path of a projectile. It is always
curved.
Projectile Motion Post Lab
Questions
3. Do the horizontal and vertical motions affect
one another? Explain your answer using the
data from your lab.
The horizontal and vertical motion of the projectile are
independent of one another!
The HORIZONTAL VELOCITY is CONSTANT (ignore air
resistance)
The VERTICAL ACCELERATION is always 9.8 m/s2
downward
Projectile Motion Post Lab
Questions
4. Write an equation that describes
horizontal motion in terms of horizontal
speed (vx), horizontal distance (dx) and
time of travel (t).
dx = vxt
Projectile Motion Post Lab
Questions
5. Write an equation that describes the vertical
motion in terms of distance fallen (dy),
vertical accel. (g) and time of travel (t).
dy =
2
½gt
Projectile Motion
Velocity can be SEPARATED into horizontal and
vertical components.
Solve vertical and horizontal parts of problem
separately.
ALL the same equations from linear motion work for
projectiles.
Time is the only quantity which is the same for both
vertical and horizontal motion.
See the Kin/Dyn Skill Sheet
Horizontal
Vertical
Example #4
A stone is thrown horizontally at 25 m/s from the
top of a cliff 53 meters high. How long does it
take the stone to reach the bottom of the cliff?
Example #4
A stone is thrown horizontally at 25 m/s from the
top of a cliff 53 meters high. How far from the
base of the cliff does the stone strike the ground?
Example #4
A stone is thrown horizontally at 25 m/s from the
top of a cliff 53 meters high. What’s the stone’s
horizontal and vertical speeds just before striking
the ground?
vfy
vfx
Example #5
Cliff divers at Hawaii dive from 65 meter high cliffs. The
rocks at the base of the cliff protrude 27 meters beyond the
edge of the cliff. What is the minimum horizontal velocity
needed to safely clear the protruding rocks?