1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Helium balloon in a decelerating car

  1. Nov 12, 2009 #1
    I was watching a program "what would happen if" (or something along that line) in NatGeo and was stunned by what i saw in it. This is the situation.
    Several helium balloons are suspended from a car's roof panel through strings (interior of the car). When the car decelerates, what direction do you think the balloons would swing to? forward? NO. That doesn't seem to be the way nature prefer. The balloons swung back in unison when the car was braked.
    The anchor said something about the air in the car rushing front and as a result a low pressure region being created at the back.. Can someone clarify this further?
    P.S: I think this thread could also be used to share other non-intuitive events.
     
  2. jcsd
  3. Nov 12, 2009 #2

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2016 Award

    When I used to teach intro physics, I had my students get onto the Chicago CTA trains with helium balloons and see what happened when the trains accelerate.

    The reason why these balloons float in the first place is that it is less dense than the air surrounding it. If you left it go, it will rise upwards because the more ends and heavier surrounding air sinks underneath the balloon and pushes it upwards.

    Same thing when you accelerate. The air surrounding the balloon will get pushed back more, and thus, displaces the balloon. The opposite occurs when you decelerate.

    BTW, this is one example where things happened counter-intuitively when one doesn't know the physics. It makes sense, and becomes intuitive when one learns a little bit more. So "intuition" in this case is nothing more than an accumulated body of knowledge.

    Zz.
     
  4. Nov 12, 2009 #3

    Ranger Mike

    User Avatar
    Science Advisor
    Gold Member

    now that is neat!
    thanks!!!!
     
  5. Nov 12, 2009 #4

    russ_watters

    User Avatar

    Staff: Mentor

    Clarification: is this a floating helium balloon or an air filled balloon hanging from the ceiling? The "suspended from the car's roof panel" part makes no sense to me.
     
  6. Nov 12, 2009 #5
    Sorry. I meant to type floor panel.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Helium balloon in a decelerating car
  1. Balloon in car (Replies: 16)

  2. Balloon Car (Replies: 3)

Loading...