Re: Getting old is not for sissies

On 3/3/2025 7:35 PM, Roger Merriman wrote:

Frank Krygowski <frkrygow@sbcglobal.net> wrote:

On 3/3/2025 10:23 AM, Roger Merriman wrote:

Frank Krygowski <frkrygow@sbcglobal.net> wrote:

On 3/2/2025 7:55 PM, Roger Merriman wrote:

Frank Krygowski <frkrygow@sbcglobal.net> wrote:
>

I submit Peter Sagan at about 0:15 in this video:
https://www.youtube.com/watch?v=Viszek1LlpA
>

I’d suggest he probably did more than just pull up, it’s fast ...

>
It helps to slow it down to half speed or slower as you view it.
>

... but looks
like he compresses and then springs up, he’s also someone with some MTB
background and likes to throw the bike about.
>
Ie that doesn’t look like just a cheap and dirty pull on the bars.

>
Reread above, please. What I said is still there:
>
"On my road bikes, I "spring up"- that is, jump my body upward. I then
pull upwards with both hands and feet. Since I use toe clips instead of
clipless, I don't think I've ever unclipped while doing that."
>
If I want to jump a bit higher and if I have time, I think I do
"compress" a bit before I spring up.
>
>

He clearly does compress ie not at all clear that he’s pulling up much if
anything...

>
Really? Let's think about this in terms of physics - of force, mass and
acceleration.
>
Unlike your mountain biker, Sagan does not use an extreme wheelstand to
raise the center of mass of the bike, allowing later rotation around
that elevated C. of M.
>
Instead, after Sagan's body rises, the bike rises in pure translation
(as opposed to rotation). Such a motion requires upward force. Without
an upward force, a body can't experience an upward translational
acceleration.
>
If Sagan is not pulling up, what would make the bike levitate?
>
>

I strongly suspect that he’d die of shame if he used that cheap and dirty
yank on the bars, like other examples it’s fast and fluid so breaking it
down into its consistency movements is always difficult which is again why
Don did the exaggeration to explain.

You're avoiding the physics of the situation. Cheap or expansive, dirty or clean, fast or slow, no bicycle (or other object) is going to rise upward in translational motion like that unless there is an upwardly directed force.
It can get more complicated if, as your mountain bike did, one introduces rotation into the motion. But Sagan did not, so the physics remains very basic.
Slow the video to 0.25 speed and watch carefully.
--
- Frank Krygowski