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Suppose a Car/Van is launched into space with you. Suppose you would like to do 'Surf' on the car roof like Marty in "Teen Wolf". On the earth, if car accelerate up to 30-50 or 100 mph will make Marty fall down because of air friction and because Marty is not "anchored" to the Van.

But what happen in empty space if car accelerate and I'm not anchored to the car roof ?

Will I get "car motion/speed" just because I'm lean on car roof ?

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stighy
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    How does an answer get positive votes for a question that gets negative votes? I generally figure that if a question stimulates an up-voted answer, then the question must have been worth something and should get a vote as well. – Greg Jun 01 '20 at 20:44
  • Technically capsules like Dragon car surf on their boosters until they reach orbit – Speedphoenix Jun 01 '20 at 21:34
  • Marty will not fall off because of air friction, but because of inertia. Same if he would be in the car and he'd not be have his belt on ... His death upon braking would hardly be due to air friction then. – AtmosphericPrisonEscape Jun 01 '20 at 21:51
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    @Greg The criteria for upvoting are different for questions and answers. For questions, they include "question shows research effort". A question without even basic research isn't worth being rewarded by an upvote, but its answers may still be useful. – TooTea Jun 02 '20 at 09:53
  • What does "in empty space" mean? In vacuum? In free-fall? Both? (probably both, right?) – Solomon Slow Jun 02 '20 at 14:53

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With no gravity there is no friction between shoes and the car roof. You'll keep floating as you were while the car will speed away... if it gets any traction between the wheels and whatever it drives on, which would be absent just the same. But maybe it has a rocket engine.

On the other hand, if you stand "sideways" on the car grill or windshield, the car's acceleration will substitute for gravity and you'll be accelerating with it... for as long as the car keeps accelerating. As soon as it cuts off into neutral, the compression force that squeezed the soles of your shoes between the car and your feet will rebound and send you flying ahead.

SF.
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  • What does As soon as it cuts off into neutral mean? – gerrit Jun 02 '20 at 08:43
  • @gerrit stops accelerating. – SF. Jun 02 '20 at 09:09
  • Why would I be sent "flying ahead" when the car stops accelerating? We'd both be in exactly the same orbit with the same forces acting on us, so unless I push myself away from the car, I shouldn't accelerate relative to it, should I? – gerrit Jun 02 '20 at 09:23
  • So you're telling me that speak about "lean on other object" in no gravity / Space doesnt' mean nothing, because of gravity 0 .. – stighy Jun 02 '20 at 09:25
  • @gerrit "the compression force that squeezed the soles of your shoes between the car and your feet will rebound" - anything missing there? Rubber soles? – SF. Jun 02 '20 at 09:28
  • @stighy: You could just as well lean on a submarine while scuba-diving. – SF. Jun 02 '20 at 09:28
  • This is technically correct in that "friction" requires a force, but there's always a tiny bit of "stickiness" from molecular bonding or electrical attraction. Yeah, I'm picking nits off an elephant. – Carl Witthoft Jun 02 '20 at 11:33
  • Good magnets in the soles would solve it. – SF. Jun 02 '20 at 14:12
  • @gerrit, Re, "Why would I be sent 'flying ahead'...?" SF said something about, "the compression force that squeezed the soles of your shoes." That's probaby a reference to elasticity. Assume that the soles of your shoes are slightly springy. They would be compressed by the acceleration. Then, when the acceleration of the "car" suddenly stopped, the soles of your shoes would expand, releasing their stored energy, and continuing to accelerate you for a brief moment, pushing you away from the car. – Solomon Slow Jun 02 '20 at 14:59
  • Of course, if your legs were bent, and you were supporting your "weight" on muscle, then you would push yourself away from the car during the moment between when the car's acceleration stopped, and when you reacted to the change. – Solomon Slow Jun 02 '20 at 15:01
  • @SolomonSlow, it doesn't even require squishy shoes or bent legs. The rocket itself gets compressed a bit during acceleration. – Mark Jun 03 '20 at 03:11