Download presentation
Presentation is loading. Please wait.
Published byPeter Daggett Modified over 9 years ago
1
Online Videos - Fake or Not? Stuff from the InterWebs Rhett Allain Dot Physics (dotphys.net) Southeastern Louisiana University
2
The Physics Suppose an object is in free fall Only one force (probably can ignore air) The acceleration is -9.8 m/s^2 down
3
Measurable Stuff Horizontal velocity = constant Vertical position should be parabolic (with time)
4
The Tools Tracker Video Analysis Get x, y, and time data from each frame http://www.cabrillo.edu/~dbrown/ tracker/
5
Video Analysisability Score Stationary camera and background Camera does not zoom Motion perpendicular to the camera You can see the object in each frame No repeating frames Downloadable Interlacing
6
Case 1: Elephant on a trampoline
7
Analysis Scale = 1 trampoline
8
Verdict: Fake Not a constant acceleration
9
Case 2: Kobe number 1
10
Problem - not a point object plot head, truck, arms, thighs, calf Kobe = 1.98 m
11
Horizontal Motion Verdict: Could be real, but faked
12
Case 3: Kobe number 2 Jumping over a pool of snakes
13
vertical motion
14
horizontal motion Verdict: No reason to say it is fake (except that it is crazy)
15
Case 4: Movie Up! Boy throws out GPS Verdict: Hello? Fake.
16
More Physics: Work-Energy Principle Human G-force (acceleration) tolerance Time (min) +Gx (eyeballs in) -Gx (eyeballs out) +Gz (blood feet) -Gz (blood head) 0.01 (sec) 3528188 0.03 (sec) 2822147 0.1 (sec) 2017115 0.3 (sec) 151294.5 1 (sec) 11973.3
17
Case 5: Hancock Not nice to call people names Not nice to throw people like that
18
The boy was in the air for 23 seconds. So, how fast did Hancock throw him? What if there is no air resistance? if acceleration = g, and no air resistance - then initial speed = final speed v initial = 113 m/s or 250 mph If the boy is accelerated over 2 meters, what would it be?
19
Air Resistance At 250 mph, air resistance plays an important role C is a coefficient of air resistance Force is in the opposite direction as v Depends on other stuff also density of air cross section area shape
20
Finding C Assume that the boy would fall at a terminal velocity similar to an adult. For a falling person: At terminal velocity, air resistance = gravity
21
How to model this motion? Problem: Net force is not constant. Break it into pieces of time that have about constant force. - Numerical Calculation Plan: Calculate the force Calculate the acceleration Update velocity Update position Update time Plot stuff
22
How fast to be in the air for 23 seconds? What if v-initial = 113 m/s with air? No air resistance air resistance
23
Keep running program with different initial velocities Record initial v and time of flight
24
Back to acceleration If the boy is thrown in 2 meters with a final speed of 400 m/s... from work-energy: Put in some numbers Verdict: I am pretty sure this is fake.
25
Case 6: Prof Splash
26
Great case for work-energy Key: what is acceleration in water? Use Work-Energy to find F-water Find acceleration
27
Findings v at water = 14.55 m/s Avg acceleration in water = 347 m/s^2 This is 35.4 g’s Verdict: NASA - Approved, real
28
Case 7: Giant Water slide jump
29
Vertical Motion Motion not always perpendicular Unknown slide height length scale = ramp
30
Other stuff Horizontal speed seems constant Accelerates in 3 seconds down the ramp - ok Risky, but possible Verdict: Fake (sometimes I get fooled also)
31
Conclusion Really, all I have to say is there are more videos at http://blog.dotphys.net
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.