Flying R2 D2 What would Aristotle Say? What would Newton Say? Does R2 fly at a constant speed? What is R2 Made of? it's just a movie Using Tracker Video Analysis This is free software (java-based)

Load a video

Scale the video

Mark an object in each frame

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

Why?

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

Earth-like gravity

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)

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# Flying R2-D2, Newton and Aristotle

Does R2-D2 fly according to the ideas of Aristotle or Newton?

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