C
Carl Sundquist
Guest
"MagillaGorilla" <[email protected]> wrote in message
news:[email protected]...
>> 'Gil,
>>
>> Thanks for the level headed response. I just scanned it 'cuz I'm headed
>> out the door for a ride, but nobody said anything about extra energy or
>> increased watts. Think of it this (perhaps not the best example) way:
>> pitchers very rarely throw over 100 mph. Tennis players serve the ball
>> 120 all the time. Even women serve faster than 100 mph. It's not
>> increased energy, it's increased distance traveled (face of the tennis
>> racquet) in an equal time over the pitcher's throwing device (arm).
>
>
> Yes, a tennis player has increased torque over a pitcher. This is why
> using a longer tire iron/wrench makes it easier to remove lug nuts.
This isn't about increased torque. A longer tire iron works because of
increased leverage on the axis point. The torque on the axis point
(shoulder) for a lithe 125 lb female tennis player is not greater than that
of a fattie major league pitcher. Torque is force needed to twist an object
an object. Power is torque * speed (in rpm) * X (X is a constant, 5250 in
the case of horsepower). If torque and rpm are equal between the pitcher and
the tennis player, what makes the difference in the speed of the ball being
thrown/hit? The lever of the tennis player (arm and racquet) has to travel
farther in it's arc than the arm of the pitcher. If the torque and rpm are
the same, the speed of the tennis racquet face has to move faster than the
pitcher's hand to achieve an equal angle of rotation because the length of
the arc is greater. Same reason the shaft of a golf club is longer the
farther you expect to hit the ball. Or think of it this way: put your kid on
the local merry-go-round. Put him/her in the middle. Spin it as fast as you
can. He will be having a great time (whereas if you were in the middle,
you'd likely be throwing up). Put your kid on the outside if the merry-go
round and he'll have to hang on for dear life because of the increased
speed. Torque to spin the merry-go-round hasn't changed, neither has rpm.
But your kid will get launched like a jai-alai pelota if he doesn't have the
Kung-Fu grip. But I think this digression of these illustrations only serve
to add to the confusion.
>
> I think why everybody is confused on this is because they are only seeing
> the small positive effect of turning on a velodrome. And this small
> positive effect (assuming Dan's calculations are accurate) is going to be
> offset by relatively larger negative effects I have cited. I don't see how
> these negative effects would be smaller than the positive effect you are
> talking about. It doesn't feel right to me.
>
> Plus, everywhere you look, things go slower in turns - NASCAR, Indy cars,
> horses, runners.
All these examples slow because of traction issues, not forces due to
changes in direction (other than traction issues). With race vehicles, some
of that can be negated by banking the turns. You can't really do that very
much with horses or runners because the the effort to resist compressive g
forces would take away from speed. Race cars don't have that issue because
the suspension is isolated from the motive forces. Bicycles, being
essentially unsprung and supporting the drive mechanisms (legs), don't have
those issues. However, if you tried to pedal out of the saddle at top speed
on the banked turns of a track you'd have the same issues as the runners and
horses.
>
> Have someone do the experiment I talked about in the LA Velodrome. I am
> positive you will see a decrease in speed on turns for a constant wattage
> output vs. that same wattage output on a straightaway.
I know this is anecdotal, but the best illustration is a team pursuit (yeah
I know, coming from me that's a big surprise). In a team pursuit maintaining
a constant, close gap between the wheels of the riders is optimal. As the
first rider enters the turn, his bike accelerates to keep the same
rotational speed as his center of mass on a slightly smaller radius. The
center of mass does not increase speed. As the first rider's bike
momentarily goes faster than the rider directly behind him (until the second
rider enter the turn and his bike speeds up too), the gap between the front
rider's rear wheel and the second rider's front wheel increases. This
increased gap slightly lessens the draft the second rider receives. The
increased gap is maintained throughout the length of the turn. Same scenario
for riders 2-3 and 3-4. You may pooh-pooh that the increased gap is
insignificant, but it is visible (on the order of 3-6 inches). Upon exiting
the turn, the front rider's bike slows down to match the rider's center of
mass. The same would happen for the following riders, meaning they would
"catch up" to the rider in front of them, as their bikes are still going
faster in the turn than the bike in front on the straight.
Ok. So far that seems simple enough: Center of mass speed stays constant
throughout, attached objects (bikes) to the outside of COM, must increase
speed in turns to maintain equal RPM with COM on a longer arc. Then
everybody and everything all catch up and even out when you hit the next
straight. Unfortunately, it isn't as simple as that. Simce increased gaps
between wheels is bad, BAD!, the riders try to maintain the same wheel gap
in the bends as on the straights. There are three ways of doing that:
Following riders "punch it" as they enter the turn to catch up, leading
riders "float" in order not speed up the bike, leading riders ride higher
on the track to increase the distance needed to travel through the bend.
Normally, the leading riders float just a bit through the turn. This also
allows the legs a small break in effort. Then as they exit the turn, the
leading riders punch it slightly to keep the following riders from stacking
up behind them.
>>
>> On the track, the speed is going to be influenced most by the center of
>> mass.
>
> On what basis do you say this? I think your premise is false. I'm
> thinking it is actually most influenced by wind resistance and rolling
> resistance, both which increase on a turn.
M = mv, where M=momentum, m=mass, v=velocity
Wind resistance is unchanged on the COM.
>
>
> In a turn, the center of mass will (ideally) stay the same speed, just
>> change direction.
>
> Okay, but I say so what? This change in direction requires a huge input of
> energy that is lost in increased friction. This loss of energy does not
> take place when going straight. This increased friction is what slows you
> down in a turn. You are only looking at one isolated positive variable of
> a turn and ignoring the negative effects.
I think (unscientifically) that the banking may negate some of the energy
loss of the change of direction. I think this because if you spin a wheel
and let it roll down the straight of a track and into the bend, at a speed
which the wheel is more or less perpendicular to the track banking, the
wheel will track through the bend on a pretty even line.
>
> I think it's very dangerous to talk about increasing speed on a bicycle in
> a turn without telling me where the extra energy is supposedly coming
> from. Saying it will come from the radius being shorted of the center of
> mass is not compelling because this defies my empirical senses.
I understand your point, but I don't think the energy needed to accelerate
the bike offsets the rotational energy of the COM on a shorter radius at an
equal rpm.
news:[email protected]...
>> 'Gil,
>>
>> Thanks for the level headed response. I just scanned it 'cuz I'm headed
>> out the door for a ride, but nobody said anything about extra energy or
>> increased watts. Think of it this (perhaps not the best example) way:
>> pitchers very rarely throw over 100 mph. Tennis players serve the ball
>> 120 all the time. Even women serve faster than 100 mph. It's not
>> increased energy, it's increased distance traveled (face of the tennis
>> racquet) in an equal time over the pitcher's throwing device (arm).
>
>
> Yes, a tennis player has increased torque over a pitcher. This is why
> using a longer tire iron/wrench makes it easier to remove lug nuts.
This isn't about increased torque. A longer tire iron works because of
increased leverage on the axis point. The torque on the axis point
(shoulder) for a lithe 125 lb female tennis player is not greater than that
of a fattie major league pitcher. Torque is force needed to twist an object
an object. Power is torque * speed (in rpm) * X (X is a constant, 5250 in
the case of horsepower). If torque and rpm are equal between the pitcher and
the tennis player, what makes the difference in the speed of the ball being
thrown/hit? The lever of the tennis player (arm and racquet) has to travel
farther in it's arc than the arm of the pitcher. If the torque and rpm are
the same, the speed of the tennis racquet face has to move faster than the
pitcher's hand to achieve an equal angle of rotation because the length of
the arc is greater. Same reason the shaft of a golf club is longer the
farther you expect to hit the ball. Or think of it this way: put your kid on
the local merry-go-round. Put him/her in the middle. Spin it as fast as you
can. He will be having a great time (whereas if you were in the middle,
you'd likely be throwing up). Put your kid on the outside if the merry-go
round and he'll have to hang on for dear life because of the increased
speed. Torque to spin the merry-go-round hasn't changed, neither has rpm.
But your kid will get launched like a jai-alai pelota if he doesn't have the
Kung-Fu grip. But I think this digression of these illustrations only serve
to add to the confusion.
>
> I think why everybody is confused on this is because they are only seeing
> the small positive effect of turning on a velodrome. And this small
> positive effect (assuming Dan's calculations are accurate) is going to be
> offset by relatively larger negative effects I have cited. I don't see how
> these negative effects would be smaller than the positive effect you are
> talking about. It doesn't feel right to me.
>
> Plus, everywhere you look, things go slower in turns - NASCAR, Indy cars,
> horses, runners.
All these examples slow because of traction issues, not forces due to
changes in direction (other than traction issues). With race vehicles, some
of that can be negated by banking the turns. You can't really do that very
much with horses or runners because the the effort to resist compressive g
forces would take away from speed. Race cars don't have that issue because
the suspension is isolated from the motive forces. Bicycles, being
essentially unsprung and supporting the drive mechanisms (legs), don't have
those issues. However, if you tried to pedal out of the saddle at top speed
on the banked turns of a track you'd have the same issues as the runners and
horses.
>
> Have someone do the experiment I talked about in the LA Velodrome. I am
> positive you will see a decrease in speed on turns for a constant wattage
> output vs. that same wattage output on a straightaway.
I know this is anecdotal, but the best illustration is a team pursuit (yeah
I know, coming from me that's a big surprise). In a team pursuit maintaining
a constant, close gap between the wheels of the riders is optimal. As the
first rider enters the turn, his bike accelerates to keep the same
rotational speed as his center of mass on a slightly smaller radius. The
center of mass does not increase speed. As the first rider's bike
momentarily goes faster than the rider directly behind him (until the second
rider enter the turn and his bike speeds up too), the gap between the front
rider's rear wheel and the second rider's front wheel increases. This
increased gap slightly lessens the draft the second rider receives. The
increased gap is maintained throughout the length of the turn. Same scenario
for riders 2-3 and 3-4. You may pooh-pooh that the increased gap is
insignificant, but it is visible (on the order of 3-6 inches). Upon exiting
the turn, the front rider's bike slows down to match the rider's center of
mass. The same would happen for the following riders, meaning they would
"catch up" to the rider in front of them, as their bikes are still going
faster in the turn than the bike in front on the straight.
Ok. So far that seems simple enough: Center of mass speed stays constant
throughout, attached objects (bikes) to the outside of COM, must increase
speed in turns to maintain equal RPM with COM on a longer arc. Then
everybody and everything all catch up and even out when you hit the next
straight. Unfortunately, it isn't as simple as that. Simce increased gaps
between wheels is bad, BAD!, the riders try to maintain the same wheel gap
in the bends as on the straights. There are three ways of doing that:
Following riders "punch it" as they enter the turn to catch up, leading
riders "float" in order not speed up the bike, leading riders ride higher
on the track to increase the distance needed to travel through the bend.
Normally, the leading riders float just a bit through the turn. This also
allows the legs a small break in effort. Then as they exit the turn, the
leading riders punch it slightly to keep the following riders from stacking
up behind them.
>>
>> On the track, the speed is going to be influenced most by the center of
>> mass.
>
> On what basis do you say this? I think your premise is false. I'm
> thinking it is actually most influenced by wind resistance and rolling
> resistance, both which increase on a turn.
M = mv, where M=momentum, m=mass, v=velocity
Wind resistance is unchanged on the COM.
>
>
> In a turn, the center of mass will (ideally) stay the same speed, just
>> change direction.
>
> Okay, but I say so what? This change in direction requires a huge input of
> energy that is lost in increased friction. This loss of energy does not
> take place when going straight. This increased friction is what slows you
> down in a turn. You are only looking at one isolated positive variable of
> a turn and ignoring the negative effects.
I think (unscientifically) that the banking may negate some of the energy
loss of the change of direction. I think this because if you spin a wheel
and let it roll down the straight of a track and into the bend, at a speed
which the wheel is more or less perpendicular to the track banking, the
wheel will track through the bend on a pretty even line.
>
> I think it's very dangerous to talk about increasing speed on a bicycle in
> a turn without telling me where the extra energy is supposedly coming
> from. Saying it will come from the radius being shorted of the center of
> mass is not compelling because this defies my empirical senses.
I understand your point, but I don't think the energy needed to accelerate
the bike offsets the rotational energy of the COM on a shorter radius at an
equal rpm.