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Flying R2-D2, Newton and Aristotle
Rhett Allainon 20 September 2010
Transcript of Flying R2-D2, Newton and Aristotle
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You get position-time data http://www.cabrillo.edu/~dbrown/tracker/ Looks pretty constant
But thrusters are angled back
Thrusters at about 43 degrees When R2 stops, thrusters point forward What should a flying rocket look like? Forces are interactions natural motions
violent motions natural motions things want to be where they should go
fire goes up
air goes up
rocks go down
you know, natural violent motion moving something from its natural state
To sum: force = motion
(hint: many people think this way and Galileo Forces CHANGE MOTION Example: Suppose I push a cart What happens when I stop pushing? Aristotle: No more violent interaction
Cart returns to natural state = at rest
No force = no motion. Period.
Newton: The cart slows down
There must be some other force
No force = no CHANGE in motion Of course - but that is what makes it fun Notice how the rocket guy is upright when flying at a constant speed?
His feet point in the opposite direction as the acceleration What if he really needs to forward thrust for constant speed?
What would that mean?
Assumptions You assume too much
air density like Earth Physics Newton says: constant speed means How about a force diagram values:
thrust angle of 35 degrees
velocity of 2.3 m/s Mass of R2 = 0.1 kg = 100 grams this would be a density of 0.1 kg/m^3
styrofoam has a density of 40 kg/m^3 WARNING:
Do not say: physicist proves R2 weighs less than styrofoam.
That would be confusing density and mass.
I weigh more than iron (more than a small piece of iron)