[ExI] scieceblind

Dan TheBookMan danust2012 at gmail.com
Fri Oct 13 16:11:54 UTC 2017


On Oct 13, 2017, at 8:49 AM, William Flynn Wallace <foozler83 at gmail.com> wrote:
>> On Thu, Oct 12, 2017 at 8:56 PM, Mike Dougherty <msd001 at gmail.com> wrote:
>> On Oct 12, 2017 7:45 PM, "William Flynn Wallace" <foozler83 at gmail.com> wrote:
>> 
>> 
>> I also thought about something not in the book:  why does a helium balloon rise?  Don't tell l me it's lighter.  My cat is lighter than I am and he is not flying around.  The gas inside the balloon must be exerting pressure in every direction, so the force cannot be from there.  Where is the force here??
>> 
>> Do you not know this or are you cleverly feigning to test the list for science blindness? 
> ​------------
> Ah, if only I were that clever.  Even if I were, I'd not pull that on y'all.  I just do not understand buoyancy.  Another example from the book has a table pushing upwards against a book lying on it.  Don't get that either.  Don't see where the force is coming from.
> 
> Lighter things rise.  I get that.  I just don't see why.

Buoyancy has to do with density of an object in a fluid medium. Your cat and you are not less dense than the air, hence (under everyday conditions) neither of you float away.

The book is pulled down by gravity (in classical mechanics). If it's being acted in by a force yet doesn't move (in an inertial frame*), then another force must must be balanced against gravity. Since the book doesn't move, then it must be acted on by an equal and opposing force. In this case the table itself is pushing up against gravity. (In fact, the book will warp the table slightly, though this is unnoticeable is most situations. But imagine a really heavy book if a table that's very flexible. By the way, I notice this with my bookshelves, which have sagged over the years.)

Anyone else, please correct me where I've gotten it wrong.

Regards,

Dan
   Sample my latest Kindle book "Sand Trap":
http://mybook.to/SandTrap

* Well, it could move with constant velocity too, but the book is doing neither approximately if we take it to be in an inertial frame.
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