[ExI] scieceblind

John Clark johnkclark at gmail.com
Fri Oct 13 16:23:12 UTC 2017


On Thu, Oct 12, 2017 at 7:34 PM, William Flynn Wallace <foozler83 at gmail.com>
 wrote:

​> ​
> In fact, I found myself in an error or two.  For instance, what he calls
> the 'normal force'
>

​
A normal force is just a force perpendicular to a surface.

​> ​
> example consists of a table and book lying on it, and says the table is
> exerting a force upwards on the book (or else the book would be pulled
> through it by gravity, which I doubt in the extreme, as both are very
> solid).  Upward force?  From where?
>

​The short answer is electrostatic repulsion. The most outer part of the
atoms on the most outer part of the book consist of negatively charged
electrons, and the same is true of the atoms in the table, and 2 negatively
charged objects repel each other. The reason this effect does not destroy
all solid objects like books and tables is because of chemistry, sometimes
2 atoms can share an electron and form a chemical bond, this would happen
if you put glue on the book and stuck it to the table. To explain why
sometimes atoms would want to share an electron and form a bond I'd have to
get into quantum mechanics.


> ​> ​
> I also thought about something not in the book:  why does a helium balloon
> rise?
>

​Gravity is indeed exerting a downward force on the balloon, but it is also
exerting a downward force on the air and because the air is heavier that
force is stronger. Air is not a solid so it can move and it moves air under
the balloon leaving the balloon nowhere to go but up.

 John K Clark
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