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On Apr 29, 2022, at 2:52 PM, John Denker via Phys-l <phys-l@mail.phys-l.org> wrote:_______________________________________________
On 4/29/22 10:20 AM, Carl Mungan via Phys-l wrote:
And I suppose even if he had used enough straps, the whole trailer
could have jack-knifed vertically up into the air?
Let's talk about that.
1) By design, most boats have a rather low center of mass.
The last non-catamaran sailboat I was on had thousands of
pounds of lead in the keel, to make it not heel too much
when on a reach.
So, even if you add in the height of the trailer, I would
expect the height of the CM to be less than half the length
of the boat. That implies to flip the thing up in the air
would require more than 1 gee of deceleration. I doubt that
the truck could achieve that.
2) The same physics leads to a different conclusion in other
situations. A person on a bicycle has a comparatively high
CM relative to length (compared to a boat). If you have good
brakes, you might be able to generate enough force to flip
yourself over the front tire.
In a panic-stop situation with a high CM, you should start
by scrunching down to lower your CM as much as possible, then
apply the front brake to the point where most of the down
force is shifted to the front, i.e. just shy of the point
where the rear wheel comes off the ground (which would result
in loss of directional control). The point is, assuming a
constant coefficient of friction and no skidding, this is
the most braking force you can achieve.
Suppose you use the back brake only. This is self-limiting,
because more braking means less down-force on the rear (and
more down-force on the front) so at some point the rear tire
starts skidding. This is suboptimal. It is far less than the
maximum possible braking.
If you have a lower CM and/or a longer bike and/or a
more rearward seat position, you don't need to worry about
flipping over the front tire. Max braking will be achieved
with "most" of the weight on the front wheel but there will
still be "some" weight on the back, so there will still be
some role for the rear brake.
3) The same physics applies to taildragger-type airplanes. A
nose-over accident is definitely possible if you apply too
much braking. Normally you can prevent this by applying
back stick (i.e. nose-up tail-down aerodynamic force) but
if (a) you are a klutz and/or (b) there is a tailwind that
robs you of aerodynamic control authority, expensive things
can happen.
https://www.youtube.com/watch?v=o4oOhumKco4
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