Re: Swimming ---Is Weight Loss Possible?

"cfreund" <[email hidden]> a écrit dans le message de news:
[email hidden]...

Quoted message said:

Forget physiology, fitness, muscle, fat. Simple physics

Work = Force * Distance
Force = Mass * Acceleration

Work = Mass * Acceleration * Distance

All other factors being equal, more work to move a greater mass.

More work is necessary to move 120kg 3000m than to move 90kg 3000m

It may be right, but it is not that simple.

When swimming at constant speed, acceleration is null: force = mass *
acceleration = 0.

The sum of the forces applied to ther body is 0.

That is, the propelling force is exactly equal to drag, and weight is equal
to buoyancy (to simplify a bit - one can "swim high" by applying downward
forces to water, with a good kick and the "Miller" force, which will allow
him to reduce drag, at the expense of using precious energy to a non
directly propulsive purpose).

Drag is not directly related to weight, but to cross-section (which is
grossly proportionnal to mass ^ (2/3)) and above all to technique.

Of course, if your velocity changes a lot during the stroke phases (as seems
to be indicated by velocity / time curves of elite swimmers), weight becomes
an even more important factor. However, I believe that velocity variation is
much more important at elite level than for rec swimmers, because drag is
much more important at high speed: elite swimmers are constantly swimming at
the limit of the hydrodynamic (Froude) wall, and stopping to apply
propulsion will instantly result in a strong negative acceleration.

-- Olivier

But is is that simple. More energy is needed to move a more massive
object.

In a frictionless environment once an object at rest remains at rest, an
object in motion remains in mostion, i.e. acceleratin=0, unless an
external force is applied.

When swimming you must overcome inertia and drag by applying force. Drag
is acceleration in the opposite direction you are trying to swim. It
slow you down. If no external force is applied you stop moving. In
order to keep moving, the external force must generate acceleration equal
to (or exceed) the accleration imposed by drag. Drag forces are
generated by friction. The swimmer must generate the forces to overcome
drag. More mass-> More Force necessary to move -> More Work

Argue technique, efficiency, hydrodynamics, etc all you want, it
complicates things beyond comprehension till it be comes philosphical.

Way back there was a statement that

"Swimming a 3000 meter workout requires a lot more energy for a 120 kilo
person than for a 90 kilo person."

A response was that:

"There is no way such a simplistic evaluation can be justified"

However, if you hold all other variables constant, it takes more energy
to move 120kg than 90kg

"Silver0l" <[email hidden]> wrote in
news:[email hidden]:

Quoted message said:

"cfreund" <[email hidden]> a écrit dans le message de news:
[email hidden]...

Quoted message said:

Forget physiology, fitness, muscle, fat. Simple physics

Work = Force * Distance
Force = Mass * Acceleration

Work = Mass * Acceleration * Distance

All other factors being equal, more work to move a greater mass.

More work is necessary to move 120kg 3000m than to move 90kg 3000m

It may be right, but it is not that simple.

When swimming at constant speed, acceleration is null: force = mass *
acceleration = 0.

The sum of the forces applied to ther body is 0.

That is, the propelling force is exactly equal to drag, and weight is
equal to buoyancy (to simplify a bit - one can "swim high" by applying
downward forces to water, with a good kick and the "Miller" force,
which will allow him to reduce drag, at the expense of using precious
energy to a non directly propulsive purpose).

Drag is not directly related to weight, but to cross-section (which is
grossly proportionnal to mass ^ (2/3)) and above all to technique.

Of course, if your velocity changes a lot during the stroke phases (as
seems to be indicated by velocity / time curves of elite swimmers),
weight becomes an even more important factor. However, I believe that
velocity variation is much more important at elite level than for rec
swimmers, because drag is much more important at high speed: elite
swimmers are constantly swimming at the limit of the hydrodynamic
(Froude) wall, and stopping to apply propulsion will instantly result
in a strong negative acceleration.

-- Olivier

"cfreund" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

But is is that simple. More energy is needed to move a more massive
object.

In a frictionless environment once an object at rest remains at rest, an
object in motion remains in mostion, i.e. acceleratin=0, unless an
external force is applied.

When swimming you must overcome inertia and drag by applying force. Drag
is acceleration in the opposite direction you are trying to swim. It
slow you down. If no external force is applied you stop moving. In
order to keep moving, the external force must generate acceleration equal
to (or exceed) the accleration imposed by drag. Drag forces are
generated by friction. The swimmer must generate the forces to overcome
drag. More mass-> More Force necessary to move -> More Work

Argue technique, efficiency, hydrodynamics, etc all you want, it
complicates things beyond comprehension till it be comes philosphical.

Way back there was a statement that

"Swimming a 3000 meter workout requires a lot more energy for a 120 kilo
person than for a 90 kilo person."

A response was that:

"There is no way such a simplistic evaluation can be justified"

However, if you hold all other variables constant, it takes more energy
to move 120kg than 90kg

One thing you're not accounting for in this oversimplification is the source
of that energy. I don't think any one seriously disputes that moving more
mass requires more energy, simply that the source of that energy isn't
definately triglycerides.

"cfreund" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Way back there was a statement that

"Swimming a 3000 meter workout requires a lot more energy for a 120 kilo
person than for a 90 kilo person."

A response was that:

"There is no way such a simplistic evaluation can be justified"

However, if you hold all other variables constant, it takes more energy
to move 120kg than 90kg

And that third quote is the reason for the second.

You're a little late off the mark here; this topic was discussed to death,
and the result was/is that

a) swimming is NOT that simple;

b) a 90kg swimmer does not necessarily use less energy to swim any
particular distance at any particular speed, compared with a 120 kg swimmer;

and

c) a 90 kg swimmer wearing a 30kg weight belt is NOT the same as a 120 kg
swimmer.

There was, of course, a lot of huffery-puffery about how smart one of the
posters thought he was; a number of pointless and off-topic diversions from
the thread; and some name-calling from a poster when fallacious arguments
were exposed, but that seems to have died down now.

"diablo" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

"cfreund" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

But is is that simple. More energy is needed to move a more massive
object.

Quoted message said:

Quoted message said:

Way back there was a statement that

"Swimming a 3000 meter workout requires a lot more energy for a 120 kilo
person than for a 90 kilo person."

A response was that:

"There is no way such a simplistic evaluation can be justified"

However, if you hold all other variables constant, it takes more energy
to move 120kg than 90kg

One thing you're not accounting for in this oversimplification is the

source

Quoted message said:

of that energy. I don't think any one seriously disputes that moving more
mass requires more energy, simply that the source of that energy isn't
definately triglycerides.

One aspect of the problem is that "cfreund" and the author of the 120/90
kilo quote are assuming that there is a closed system consisting solely of
the swimmer's body - a simplification which cannot be justified.

"cfreund" <[email hidden]> a écrit dans le message de news:
[email hidden]...

Quoted message said:

But is is that simple. More energy is needed to move a more massive
object.

That's false.
At constant speed and for equal drag, the same energy is needed, whatever
the weight of the body is.

Quoted message said:

In a frictionless environment once an object at rest remains at rest, an
object in motion remains in mostion, i.e. acceleratin=0, unless an
external force is applied.

Yes.

Quoted message said:

When swimming you must overcome inertia and drag by applying force. Drag
is acceleration in the opposite direction you are trying to swim.

You are not serious, are you?
It's amazing how the simplest physicsd concept can be misunderstood.

First, if you swim at constant speed, you don't have to overcome what you
call "inertia".

Second, drag is not acceleration: drag is a force.

Acceleration is dv/dt, that is variation of speed per unit of time of a
given point (in this case: the swimmer Center of Mass).

Quoted message said:

It
slow you down. If no external force is applied you stop moving. In
order to keep moving, the external force must generate acceleration equal
to (or exceed) the accleration imposed by drag.

You are completely confusing "force" and "acceleration".

Physics only says that:

sum(all the forces applied to the body) = mass * dv/dt

There is no acceleration generated by propulsive force and acceleration
generated by drag canceling each other.

There is only a propulsive force and drag canceling each other, to generate
a null acceleration, that is a constant speed.

The consequence of that, is that the force needed to move an object with a
given drag at constant speed is independant of the mass of the object. Force
must only be strictly equal to Drag.

Quoted message said:

Drag forces are
generated by friction. The swimmer must generate the forces to overcome
drag. More mass-> More Force necessary to move -> More Work

Complete [censored].

Take 2 torpedos, one heavy and one light, with exactly the same shape and
size: they will need exactly the same power to move at the same horizontal
speed.

You will answer that a heavier boat will need more power, but that is just
because a heavier boat will have more underwater volume (more buoyancy is
needed to compensate the weight) and "wet surface", and therefore will
generate more drag.

This said, I confirm that an heavier swimmer will need more power, but not
for the reasons you mention:
- he will need more power because his cross-section and his wet surface is
larger
- he will need more power because he is not cruising at constant speed, but
continuously accelerating and decelerating during the different stroke
phases
- he will need more power because of the internal forces of the swimmer (as
opposed to propulsive forces applied to water: rotating the arms, moving the
legs up and down...)

Re-read your physics 101. And try to understand. Or ask your mom.

-- Olivier