# Re: physics question about pull ups

On Apr 21, 6:03 am, JJ Sinclair <john.sincl...@xxxxxxx> wrote:
On Apr 20, 6:35 pm, jim archer <archerz...@xxxxxxxxx> wrote:

On Apr 20, 6:17 pm, "Paul Remde" <p...@xxxxxxxx> wrote:

Hi Jim,

It is simple high school physics.  Yes the heavier glider has much more
energy, but it also takes much more energy to lift the heavier glider..  You
would be much more tired after carrying 100 pounds up a flight of stairs
than you would be after lifting 10 pounds up a flight of stairs.  The
physics shows very clearly that the extra speed energy from the higher
weight is exactly cancelled by the extra energy required to raise the
heavier weight.

before pullup            after pullup
1/2 mv^2 + mgh  = 1/2mv^2 + mgh

As you can see in the equation above you can divide both sides by m and the
equation doesn't change. So the mass of the glider doesn't matter, but the
speeds have a big effect because the velocity is squared.

Paul Remde

"jim archer" <archerz...@xxxxxxxxx> wrote in message

news:30cfc650-1aaf-4c7d-8b57-2b5d28ea2813@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Apr 20, 1:41 pm, Chris Reed <chris.r...@xxxxxxxxxxxxxxxx> wrote:

aak...@xxxxxxxxx wrote:
The effect of drag on height recovery isn't too bad, but is enough to
matter.

In a low-performance glider the drag can be extremely significant. In,
say, a K8 or (I'd guess) an I-26, the height gain is very small in
comparison with 40:1 glass.

A pilot flying at the UK Juniors a few years ago described a racing
finish in a K8, producing no more than a 200 ft climb from a 90kt
pull-up. He said that a K8 in this mode was the ultimate efficient
machine "for converting height into noise".

back to the original question...

Maybe I'm missing something, but I think the approach to the problem
is flawed.   How does mass "cancel out" if they are different masses?
Total energy is not the same in each case.  All things being equal at
the pull up, speed, glider type, etc. a ballasted glider has more mass
and thus more kinetic energy which would result in a higher climbout
compared to a non ballasted glider.  I'm not going to attempt to write
the equation because that would be embarrasing for me.   But what am I
missing?  Even if we start the gliders before the dive at the same
height the result is the same, the heavier glider has more potential
energy and will have a higher climb.  Isn't this simple high school
phyics?

I understand now what you mean, the mass is the same at the bottom and
top for each glider and therefore the climb is the same height if
velocity is the same.  Interesting.  Why does it feel like you climb
so much higher with ballast?- Hide quoted text -

- Show quoted text -

Most of us would be dumping our water ballast as we climbed, does that
make the ship gain more altitude? This is an old argument and I have
always believed the heavier ship gains more altitude.
JJ

Nope dumping the water loses you energy proportional to the mass of
the water, that energy no longer lifts that weight of water higher. In
the simple potential/kinetic energy model there is no effect.

AS stated by others I expect the perceived benefit of extra weight is
due to you more likely to be flying faster if ballasted and therefore
get a higher zoom climb.

Darryl
.

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