Conversation at work - Could this be another Karl?

[CantSayBien]

Im pretty sure second person is right, but then again its been a while since I took physics. But i distinctly remember a problem with a juggler standing on some scales, and the solution was that the scales read the weight of him + 3 juggling balls. Seems like the same reasoning should apply to the truck.

[Bidlin]

Im pretty sure second person is right, but then again its been a while since I took physics. But i distinctly remember a problem with a juggler standing on some scales, and the solution was that the scales read the weight of him + 3 juggling balls. Seems like the same reasoning should apply to the truck.

On average the weight equals him and his balls, but there is fluctuation. The missing weight of airborne balls is countered by the force of throwing and catching them.

Consider what happens if the juggler gets a bit cheeky and doesn't catch a ball and it falls beside the scale. At which point does the scale realize this and change the reading?

[CantSayBien]

Yeah I was talking average weight. It seems to imply that a bunch of birds flying around in the truck weighs essentially the same (of course theres the slight offset at the start due to the jumping, but that can be made to have an arbitrarily small impact on the average, provided they fly around for long enough afterwards)

Of course, if birds can get in and out (or even if air can get in and out) then the whole argument falls apart

[Martin]

On average the weight equals him and his balls

[Calum]

i didn't read any of that tripe, but on a similar note to the responses, i've always wondered why if i drop something in a car it doesn't go to the back of the car. when moving. if that makes sense.

[monkeysandthat]

calum there waiting for the world to fall.

[ScottHanson]

Also, if you're sitting in a car without a seatbelt on, how comes you're not just pinned to the back windscreen.

[ike]

I must admit I did have a similar thought once when I was younger and saw a fly buzzing around on a plane, couldn't figure out what was stopping it from just whizzing straight to the back of the plane, given that a Boeing 747 is flying at around 700 mph or there abouts, so the fly would have to be moving at that same speed to stay in the same place....

[Nill Demand]

Magic.

[Gtpod]

i didn't read any of that tripe, but on a similar note to the responses, i've always wondered why if i drop something in a car it doesn't go to the back of the car. when moving. if that makes sense.

This man works for/with the British government.

[CantSayBien]

Intertia innit. Same reason that when you jump in the air, the planet earth doesn't fly underneath you at hunderds of kilometers per second as it orbits the sun

[Spuddy]

Intertia innit. Same reason that when you jump in the air, the planet earth doesn't fly underneath you at hunderds of kilometers per second as it orbits the sun

I thought it did but you always landed back in the same place because it spins once in the time of a jump.

[mars bah bah bah]

This thread delivered.

[Bret]

F'ing magnets - how do they work?

[MarsBarBarBar]

The following conversation was forwarded to me under the heading "He's just like KP".

Now I know both parties and while they agree their conversations take on a RG-KP theme, they argue as to who is more like KP.

Make up your own minds and let me know.

(Names have been changed to protect the innocent/guilty)
"First person" :
  YOU KNOW THAT thing about birds on lorries jumping at the same time
"Second person" :
  yes
"Second person" :
  what about it?
"First person" :
  well i think the lorry will weigh less in certain circumstances
"Second person" :
  what circumstances
  bear in mind here, this isnt an area of science thats open for debate.
"First person" :
  ok
  you have your lorry
  but the bird cages are really high
  when the birds fly they are pushing down with their wings
  BUT
"Second person" :
  yup
  k
"First person" :
  if they stop flying they drop
  while they are droping they are not push enough air down to support their weight
  ergo the lorry is lighter
"Second person" :
  what are they falling through?
"First person" :
  the air?
"Second person" :
  taadaa
  they are pushing the air down as they fall
"First person" :
  this isnt a bird shaped column
"Second person" :
  it doesnt matter
"First person" :
  they are falling because they arent pushing enough air down
"Second person" :
  the weight stays the same
  yes, they are falling because they're not pushing enough air to stay in one spot
  but while they're falling they are pushing the air below them with the force of their weight
"First person" :
  im skepical
"Second person" :
  I know
  doesnt mean its not true
"First person" :
  what about - they are in a vacuum
"Second person" :
  then they couldnt be flying
"First person" :
  they jumped
"Second person" :
  and
"First person" :
  probably cos they couldnt breath
"Second person" :
  actually they'd be exploding, but thats not the point
"First person" :
  and while falling the lorry weiaghs less
"Second person" :
  when they jumped they exerted a downward force.  For every action there is an equal and opposite reaction.  There jump up would have pushed the lorry down.
  pushing something down equates to weight
  I'm sure the physics works out exactly so that that becomes canceled out the moment they land again
  if they havent exploded that is 
"Second person" :
  I can see where your problem is.
  your idea about just before they fall they are weightless
  its not true
  you're never weightless
"Second person" :
  when you're falling it simulates being weightless, but thats only your perception because you're acelerating at the same rate as gravity .
"First person" :
  youve jumped
  the scales have dipped
  returned to zero
  you stop in mid air
  you are not pushing down on the air yet
"Second person" :
  you are
"First person" :
  no you arent
"Second person" :
  yes you are
"First person" :
  no
  you are at the tipping point
"Second person" :
  there is no tipping point
"First person" :
  your speed in either direction is zero
"Second person" :
  your speed while you're on the ground is zero
  it doesnt mean you're not pushing down
"First person" :
  if your hand was below the body you wouldnt feel any weight
"Second person" :
  you dont anyway
  you're also working on the misaprehension that air is weightless
"First person" :
  no im not
  the body isnt acting on the air in any way
"Second person" :
  yes
  it
  is
  it just hasnt pushed it out of the way yet
"First person" :
  is the air being moved by the object?
"Second person" :
  its being pressed
"First person" :
  not by the object
"Second person" :
  look.  you can argue the toss over this as much as you want
  it doesnt change the fact that your wrong
  observably wrong
"First person" :
  but you cant expalain it
"Second person" :
  this isnt just a thought experiment.  This is backed up by observable science
  in a closed system the mass is constant, wherever the items are inside the closed system
  you cant find a loophole
  as i said yesterday.  the laws of physics arent going to turn around and say, "hang on a sec.  You've got me there"

tl;dr