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OK, so here's an irritating problem...
A while back I bought an external sound card. I'm very happy with it by
the way. But then I unplugged my microphone from my PC's built-in sound
card and plugged it into the external one. I can't hear a damned thing.
"OK, so it needs a line input" I thought. So I went out and bought a
microphone preamp. And you know what?
I still can't hear anything.
To be fair, without the preamp, if I amplify the digital signal all I
get is noise. But with the amp, if you apply about 90 dB of
amplification, you can very faintly detect any loud noises made directly
in front of the mic.
Can anybody explain to me (A) why the mic is still too damned quiet, and
(B) how to make it loud enough to be useable?
[Remember, if I plug it into my motherboard sound card and turn on the
"boost mic" option, it works perfectly. But the outboard sound card has
no such option.]
Just as a point of interest... I have a knackered old mic that I got for
£5 about 15 years ago. If I plug that in through the preamp it works
just fine. [Although it's still a little on the quiet side. And that mic
never did have any treble response at all.] The mic I'm trying to use
was sold as a PC microphone, and indeed if you plug it into any PC and
turn on the mic boost option, it works just dandy. [And gives a vastly
superior sound quality to my ancient mic.]
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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My guess is that it's just picking up the wrong input in the app. The
mic probably works fine (try plugging it into the mobo mic jack and see
if it behaves properly).
Jim
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"Orchid XP v8" <voi### [at] dev null> a écrit dans le message de news:
48501913$1@news.povray.org...
> OK, so here's an irritating problem...
>
Maybe this microphone is an electret one and need to be powered (whitch your
motherboard microphone input does but not your additionnal soundcard)
Maybe you need to switch something like 'plugin power' somewhere (either
hardware or software switch).
Be careful your preamp may have a ' 48v phantom power' option but it is way
too much for a PC microphone.
Marc
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> A while back I bought an external sound card. I'm very happy with it by
> the way. But then I unplugged my microphone from my PC's built-in sound
> card and plugged it into the external one. I can't hear a damned thing.
As Marc said, your microphone is probably a powered one, and PC sound cards
normally provide power on the mic socket.
> "OK, so it needs a line input" I thought. So I went out and bought a
> microphone preamp. And you know what?
>
> I still can't hear anything.
The pre-amp is probably expecting a real microphone, not one that needs
power.
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"scott" <sco### [at] laptopcom> a écrit dans le message de news:
4850cbf8$1@news.povray.org...
>
> The pre-amp is probably expecting a real microphone, not one that needs
> power.
>
Some top-notch microphones need power :-)
on professionnal equipment 48V DC phantom power through ballanced wiring is
commonly used.
http://en.wikipedia.org/wiki/Phantom_power
But as I said it does not fit to PC microphones that use plugin power
A detailed arcticle :
http://www.epanorama.net/circuits/microphone_powering.html
Marc
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>> OK, so here's an irritating problem...
>>
> Maybe this microphone is an electret one and need to be powered (whitch your
> motherboard microphone input does but not your additionnal soundcard)
> Maybe you need to switch something like 'plugin power' somewhere (either
> hardware or software switch).
Actually I'm pretty sure my PC microphone is a crystal mic...
[The microphone that works is marked as "dynamic", whatever that means.]
I had a go with my dad's test meter. At 0 Hz, the working mic has a
resistence of about 600 Ω, whereas the non-working one is about 1.2 kΩ.
I don't know whether that has anything to do with anything. [I don't
have the specifications for my outboard sound card to hand...]
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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"Invisible" <voi### [at] devnull> a écrit dans le message de news:
4850f855@news.povray.org...
> Actually I'm pretty sure my PC microphone is a crystal mic...
UH? do they still sell that? Usually they are electrets
>
> [The microphone that works is marked as "dynamic", whatever that means.]
It means a moving coil microphone, no need for power
>
> I had a go with my dad's test meter. At 0 Hz, the working mic has a
> resistence of about 600 ?, whereas the non-working one is about 1.2 k?. I
> don't know whether that has anything to do with anything. [I don't have
> the specifications for my outboard sound card to hand...]
For the dynamic microphone you measure the DC resistance of the coil .
Electret microphone are buffered by a FET and insulated from DC by a
capacitor.
You can't measure a useable impedence at 0 Hz :-)
maybe you measured between rim (power +) and sleeve (ground)
http://en.wikipedia.org/wiki/Electret_microphone
Marc
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>> Actually I'm pretty sure my PC microphone is a crystal mic...
> UH? do they still sell that? Usually they are electrets
Sure - why not? They sell crystal ear pieces too - very useful with
home-made crystal radio sets. And let's not forget, picture speakers use
crystals too...
>> [The microphone that works is marked as "dynamic", whatever that means.]
>
> It means a moving coil microphone, no need for power
Right. So a reverse speaker then?
>> I had a go with my dad's test meter. At 0 Hz, the working mic has a
>> resistence of about 600 ?, whereas the non-working one is about 1.2 k?. I
>> don't know whether that has anything to do with anything. [I don't have
>> the specifications for my outboard sound card to hand...]
> For the dynamic microphone you measure the DC resistance of the coil.
Right. So the working mic has a DC resistence of 600 Ω.
> Electret microphone are buffered by a FET and insulated from DC by a
> capacitor.
> You can't measure a useable impedence at 0 Hz :-)
OK. So assuming it really is electret, I can't measure its impedence
meaningfully.
I'm 70% sure this is the guy BTW:
http://www.maplin.co.uk/module.aspx?ITAG=SPEC&ModuleNo=24698&doy=12m6#spec
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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"Invisible" <voi### [at] devnull> a écrit dans le message de news:
4850ff36$1@news.povray.org...
>>> Actually I'm pretty sure my PC microphone is a crystal mic...
>
>> UH? do they still sell that? Usually they are electrets
>
> Sure - why not? They sell crystal ear pieces too - very useful with
> home-made crystal radio sets. And let's not forget, picture speakers use
> crystals too...
The frequency response of crystal microphones is often limited to a
relatively narrow band . They boost treeble and have poor basses.
It may be good for a close-miking of voice to enhance speach recognition but
they are far from all-purpose applications.
>
>> It means a moving coil microphone, no need for power
>
> Right. So a reverse speaker then?
Exactly but not optimized for that use :-)
>
>
> OK. So assuming it really is electret, I can't measure its impedence
> meaningfully.
>
> I'm 70% sure this is the guy BTW:
>
> http://www.maplin.co.uk/module.aspx?ITAG=SPEC&ModuleNo=24698&doy=12m6#spec
The *stereo* (the exact name is TRS for Tip/Rim/Sleeve) jack for a mono
microphone makes me suspect it is an elecret.
The rim is for power +.
Marc
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>>> It means a moving coil microphone, no need for power
>> Right. So a reverse speaker then?
>
> Exactly but not optimized for that use :-)
Mmm - I understand you can also make a mic out of a speaker. But it
tends not to work well. ;-)
Hey, I wonder - can I use the alternator on my car to drive the car
instead of recharge the battery? :-D
>> I'm 70% sure this is the guy BTW:
>>
>> http://www.maplin.co.uk/module.aspx?ITAG=SPEC&ModuleNo=24698&doy=12m6#spec
>
> The *stereo* (the exact name is TRS for Tip/Rim/Sleeve) jack for a mono
> microphone makes me suspect it is an elecret.
> The rim is for power +.
Hmm... a stereo jack on a mono microphone... yeah, that does seem a
little suspect.
Oh goodie. Now I need to find some power from somewhere. :-/
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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"Invisible" <voi### [at] devnull> a écrit dans le message de news:
48512450$1@news.povray.org...
>
> Oh goodie. Now I need to find some power from somewhere. :-/
>
> --
Out of curiosity, whitch model is your additionnal soundcard?
Marc
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Invisible wrote:
> Mmm - I understand you can also make a mic out of a speaker. But it
> tends not to work well. ;-)
That's how the very first telephones worked. By the time they actually
got to something like a switchboard (i.e., telephone rather than
intercom) they figured they could separate the two.
> Hey, I wonder - can I use the alternator on my car to drive the car
> instead of recharge the battery? :-D
Yes. It's called a starter motor. ;-)
--
Darren New / San Diego, CA, USA (PST)
Helpful housekeeping hints:
Check your feather pillows for holes
before putting them in the washing machine.
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>> The pre-amp is probably expecting a real microphone, not one that needs
>> power.
>
> Some top-notch microphones need power :-)
I was going to say... it's usually only *expensive* mics that need power
[which is why I'm surprised that a £4.99 mic would need it]. Usually
only expensive studio equipment provides this power too...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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> Hey, I wonder - can I use the alternator on my car to drive the car
> instead of recharge the battery? :-D
Probably with half a dozen, I'd guess they'd be 2 - 5 HP each,
would need a good DC to 3 phase controller of course.
http://www.diyelectriccar.com/forums/showthread.php/alternator-motor-conversion-booklet-2959.html
It might be a cheap way to drive one of those carts they
get the HS students to race at the enviro-fairs.
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Darren New wrote:
>> Hey, I wonder - can I use the alternator on my car to drive the car
>> instead of recharge the battery? :-D
>
> Yes. It's called a starter motor. ;-)
The starter motor is designed to convert electric to kinetic. The
alternator is designed to convert kinetic to electric. I'm musing over
whether either device can do the *opposite* job. :-P
Actually, you laugh, but I did see a report about a car that has a giant
motor inside it that drives the wheels at low speeds, acts as a starter
motor to start the petrol engine when the car is moving fast enough, and
acts as an alternator to charge the batteries thereafter. Basically the
petrol engine only runs while the car is doing more than 20 MPH. The big
advantage being that waiting at traffic lights uses no fuel.
[Actually, having computed that my car uses 10^(-6) L of fuel per minute
even when it's flying down the road at 75 MPH, I wonder just how much
fuel it can possibly be wasting on tickover? And also, doesn't
repeatedly starting up a petrol engine waste fuel anyway?]
Last I heard the car never came to market. They were still playing with
the control software to try to figure out the most optimal algorithms...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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m_a_r_c wrote:
> Out of curiosity, whitch model is your additionnal soundcard?
Behringer F-Control Audio FCA202 (I think!)
Unbalanced input impedance = 24 kΩ, max level = 2 dBV.
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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> Actually, you laugh, but I did see a report about a car that has a giant
> motor inside it that drives the wheels at low speeds,
A useful tip that (apparently) not many people know, is that if you've
broken down in a dangerous location you can use the starter motor to move
along at slow speeds in *any* car (ok maybe not in those american
automatics). Just put it in 1st gear and try to start the engine - it will
allow you to move the car to a safer location (assuming you don't also have
a flat battery!).
> The big advantage being that waiting at traffic lights uses no fuel.
My car does that already - as soon as you are stationary, in neutral, and
let go of the clutch pedal, the engine stops. And then as soon as you touch
the clutch pedal it restarts. Apparently meant to save a few % of fuel when
driving in cities.
> [Actually, having computed that my car uses 10^(-6) L of fuel per minute
> even when it's flying down the road at 75 MPH,
Wow! What car do you have with such great fuel economy? ;-)
> I wonder just how much fuel it can possibly be wasting on tickover?
I had a Ford once that showed the fuel economy in realtime as you were
driving, but if you were stopped it switched to litres per hour, was
something like 1.5 litres per hour IIRC when stationary. I rememeber
figuring out I could leave it running for a day or so until it used up a
full tank.
> And also, doesn't repeatedly starting up a petrol engine waste fuel
> anyway?]
Depends how warm the engine is and how often you restart it. For a fully
warm engine I think that if you're going to let it idle for more than a few
seconds it's better to switch it off and restart.
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> A useful tip that (apparently) not many people know, is that if you've
> broken down in a dangerous location you can use the starter motor to
> move along at slow speeds in *any* car (ok maybe not in those american
> automatics). Just put it in 1st gear and try to start the engine - it
> will allow you to move the car to a safer location (assuming you don't
> also have a flat battery!).
The thing I find interesting is that my car weighs easily enough to
crush every single bone on your body... and yet it's not actually that
hard to push it along a road. If it's parked on the drive and I need to
move it a few feet to open the guarage door or something, take the
brakes off and push it... it moves surprisingly easily for such a damn
heavy object. (I guess my wheel baring work really well?)
OTOH, if there's a hill... forget it.
(Also curios is the fact that the car doesn't accelerate when you drive
it down a hill... You'd think it would.)
>> The big advantage being that waiting at traffic lights uses no fuel.
>
> My car does that already - as soon as you are stationary, in neutral,
> and let go of the clutch pedal, the engine stops.
Mmm, interesting.
I would think this electric motor trickery probably also saves fuel on
low-speed manovers like trying to park. [Think how much you have to rev
the engine to make a car move that slowly...]
>> [Actually, having computed that my car uses 10^(-6) L of fuel per
>> minute even when it's flying down the road at 75 MPH,
>
> Wow! What car do you have with such great fuel economy? ;-)
...OK, so maybe it wasn't exactly 10^(-6). But it worked out to be some
absurdly small figure anyway.
>> I wonder just how much fuel it can possibly be wasting on tickover?
>
> something like 1.5 litres per hour IIRC when stationary.
Interesthing. I thought it would be smaller...
>> And also, doesn't repeatedly starting up a petrol engine waste fuel
>> anyway?]
>
> Depends how warm the engine is and how often you restart it.
I've always wanted to know... An engine is a mechanical device. So why
does temperature have any effect on anything?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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"Invisible" <voi### [at] devnull> a écrit dans le message de news:
48524503$1@news.povray.org...
> m_a_r_c wrote:
>
>> Out of curiosity, whitch model is your additionnal soundcard?
>
> Behringer F-Control Audio FCA202 (I think!)
>
> Unbalanced input impedance = 24 k?, max level = 2 dBV.
>
> --
> http://blog.orphi.me.uk/
> http://www.zazzle.com/MathematicalOrchid*
this one then?
http://www.behringer.com/FCA202/index.cfm?lang=ENG
If I read correctly the specs sheet, it has a dual line input, no microphone
input.
you need a preamp providing plugin power to get your pc microphone working
with it.
Marc
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"Invisible" <voi### [at] devnull> a écrit dans le message de news:
485259b1$1@news.povray.org...
.
>
> I've always wanted to know... An engine is a mechanical device. So why
> does temperature have any effect on anything?
>
http://en.wikipedia.org/wiki/Flash_point :-)
Marc
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> The thing I find interesting is that my car weighs easily enough to crush
> every single bone on your body... and yet it's not actually that hard to
> push it along a road.
...
> (I guess my wheel baring work really well?)
I guess they design them to be pretty good :-)
> (Also curios is the fact that the car doesn't accelerate when you drive it
> down a hill... You'd think it would.)
Press the clutch and start off at 5mph so as to avoid any air drag. It
should accelerate then.
> I would think this electric motor trickery probably also saves fuel on
> low-speed manovers like trying to park. [Think how much you have to rev
> the engine to make a car move that slowly...]
Ermm, my car moves just by lifting the clutch gently, no need to rev at all.
> ...OK, so maybe it wasn't exactly 10^(-6). But it worked out to be some
> absurdly small figure anyway.
IIRC you meant that amount per revolution of the engine, not per minute!
> I've always wanted to know... An engine is a mechanical device. So why
> does temperature have any effect on anything?
Things expand with temperature, an engine is designed to run smoothly at
it's operating temperature, below that there is a lot more friction.
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Invisible wrote:
> The starter motor is designed to convert electric to kinetic. The
> alternator is designed to convert kinetic to electric. I'm musing over
> whether either device can do the *opposite* job. :-P
If you essentially disengage the safeties and get them hooked up right,
yes. But since the starter motor is designed to start a car that isn't
running, there are (for example) no mechanisms to let you mesh the gears
when the motor is already running. Try turning the key when the car is
already running and you'll see what I mean.
Similarly, the generator (if you have one) really only kicks in when
you're already going more than about 20MPH, and the alternator does
funky things to keep drawing power even at low RPMs without stalling you
out.
> doesn't repeatedly starting up a petrol engine waste fuel anyway?]
Depends on whether it's carburated or fuel-injection. With fuel
injection, there's no "ramp up" to get the fuel from the tank to the
engine, no already-carburated fuel sitting in pipes and then going to
waste or evaporating, etc. It used to be starting a car used 90 to 300
minutes worth of idle-speed fuel. Nowadays, it uses maybe 2 seconds
worth, or less with cars designed to turn on and off like the hybrids.
> I've always wanted to know... An engine is a mechanical device. So why
> does temperature have any effect on anything?
It's a mechanical device that derives power from the difference in
temperature between the inside and the outside.
In the same way, a balloon zings around the room when you blow it up and
let it go, but falls to the ground when it runs out of air.
--
Darren New / San Diego, CA, USA (PST)
Helpful housekeeping hints:
Check your feather pillows for holes
before putting them in the washing machine.
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>> (Also curios is the fact that the car doesn't accelerate when you
>> drive it down a hill... You'd think it would.)
>
> Press the clutch and start off at 5mph so as to avoid any air drag. It
> should accelerate then.
Oh, it *does* accelerate... just... not very much. I mean, if you point
a *bicycle* downhill, it takes off like a rocket. And it doesn't even
weigh much! But a much heaveir car... doesn't seem to pick up speed very
much.
>> I would think this electric motor trickery probably also saves fuel on
>> low-speed manovers like trying to park. [Think how much you have to
>> rev the engine to make a car move that slowly...]
>
> Ermm, my car moves just by lifting the clutch gently, no need to rev at
> all.
Is your car diesel by any chance?
>> ...OK, so maybe it wasn't exactly 10^(-6). But it worked out to be
>> some absurdly small figure anyway.
>
> IIRC you meant that amount per revolution of the engine, not per minute!
Right. So given that there's roughly 10^3 revolutions per minute, that
would be about 10^(-3) L per minute. ;-)
>> I've always wanted to know... An engine is a mechanical device. So why
>> does temperature have any effect on anything?
>
> Things expand with temperature, an engine is designed to run smoothly at
> it's operating temperature, below that there is a lot more friction.
Ah, I see. That would make sense...
[I guess the same goes for the oil. It's probably a tad thick at 20°C.]
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Invisible wrote:
> Actually, you laugh, but I did see a report about a car that has a giant
> motor inside it that drives the wheels at low speeds, acts as a starter
> motor to start the petrol engine when the car is moving fast enough, and
> acts as an alternator to charge the batteries thereafter. Basically the
> petrol engine only runs while the car is doing more than 20 MPH. The big
> advantage being that waiting at traffic lights uses no fuel.
>
> [Actually, having computed that my car uses 10^(-6) L of fuel per minute
> even when it's flying down the road at 75 MPH, I wonder just how much
> fuel it can possibly be wasting on tickover? And also, doesn't
> repeatedly starting up a petrol engine waste fuel anyway?]
>
I'm having trouble with that math, but it could be that I haven't looked
at a diesel car in a while. My sisters car got, lets say 35 miles per
gallon when running at mostly highway speeds. I'm probably
underestimating it a bit, it was a small car. At 70 mph, that's 2
gallons of fuel an hour. 3.78 liters in 30 minutes, gets .12ish liters
per minute.
Unless you are coasting all the way downhill in both directions.
> Last I heard the car never came to market. They were still playing with
> the control software to try to figure out the most optimal algorithms...
>
They have gotten it working, the Toyota Prius does just that. It can run
on the electric motors up to around 35 MPH, and cuts the petrol engine
off when ever it doesn't need it. The batteries for the electric system
charges off of both the petrol system and a regenerative braking system.
What's really odd is riding in one of these cars when the petrol engine
cuts off at highway speeds. The car just decides that going down hill is
easy, and the driver is braking anyways, so who needs the engine?
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"Orchid XP v8" <voi### [at] devnull> a écrit dans le message de news:
4852b62f$1@news.povray.org...
>
> Oh, it *does* accelerate... just... not very much. I mean, if you point a
> *bicycle* downhill, it takes off like a rocket. And it doesn't even weigh
> much! But a much heaveir car... doesn't seem to pick up speed very much.
>
Ask Galileo :-)
Marc
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>> [Actually, having computed that my car uses 10^(-6) L of fuel per
>> minute even when it's flying down the road at 75 MPH, I wonder just
>> how much fuel it can possibly be wasting on tickover? And also,
>> doesn't repeatedly starting up a petrol engine waste fuel anyway?]
>>
>
> I'm having trouble with that math, but it could be that I haven't looked
> at a diesel car in a while.
Don't worry about it. I plucked 10^(-6) L out of the air. My point was,
during recent calculations it showed up that just coasting along uses
surprisingly little fuel. (I calculated that the amount of fuel injected
into each cylinder is drastically less than 1 drop. Which, obviously, is
impossible. The fuel would have to be vapourised or something, otherwise
surface tension would simply prevent you injecting such an absurdly tiny
volume.)
My [petrol] car can to 75 MPH at roughly 45 MPG. Let's do some math...
75 miles/hour = 1.25 miles/minute.
45 miles/gallon = 204 miles/litre.
204 miles/litre = 0.0049 litre/mile.
1.25 miles @ 0.0049 liter/mile = 0.0061 litre.
So we have roughly 6.1 * 10^(-3) L/minute. That's 6.1 mL per minute.
That's, like, one teaspoon of fuel per minute, while rocketing along at
75 MPH. What the hell the engine uses while idling has surely got to be
even smaller than this...
>> Last I heard the car never came to market. They were still playing
>> with the control software to try to figure out the most optimal
>> algorithms...
>>
>
> They have gotten it working, the Toyota Prius does just that. It can run
> on the electric motors up to around 35 MPH, and cuts the petrol engine
> off when ever it doesn't need it. The batteries for the electric system
> charges off of both the petrol system and a regenerative braking system.
>
> What's really odd is riding in one of these cars when the petrol engine
> cuts off at highway speeds. The car just decides that going down hill is
> easy, and the driver is braking anyways, so who needs the engine?
The reporter I saw remarked how eerie it is when you pull up at some
traffic lights and the engine goes silent...
Personally, it still kinda weirds me out that when a train is about to
get moving, it makes this loud whirring noise, and starts moving, and
then the whirring shuts up and the train accelerates MORE. o_O
[Of course, the noise you can hear is actually the hydraulics for the
brake system or something - it has nothing to do with the more or less
silent motors that actually drive the train along.]
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Orchid XP v8 wrote:
> 45 miles/gallon = 204 miles/litre.
PWN3D!
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Let's try that again, shall we?
75 miles/hour = 1.25 miles/minute.
45 miles/gallon = 9.89 miles/litre.
9.89 miles/litre = 0.101 litre/mile.
1.25 miles * 0.101 liter/mile = 0.126 liters
So now we have 0.126 liters/minute - a considerably larger value. (About
a third of a coke can.) Still surprisingly small given the insane
velocity involved.
(For what it's worth... I'm currently debugging a partial predictive
matching engine that keeps telling me that symbol A currently has a 130%
probability of being seen next. *sigh*)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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On Fri, 13 Jun 2008 21:18:54 +0200, "m_a_r_c"
<jac### [at] wanadoofr> wrote:
>
>"Orchid XP v8" <voi### [at] devnull> a écrit dans le message de news:
>4852b62f$1@news.povray.org...
>>
>> Oh, it *does* accelerate... just... not very much. I mean, if you point a
>> *bicycle* downhill, it takes off like a rocket. And it doesn't even weigh
>> much! But a much heaveir car... doesn't seem to pick up speed very much.
>>
>Ask Galileo :-)
>
No one expects the Spanish inquisition :)
--
Regards
Stephen
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Orchid XP v8 wrote:
> Oh, it *does* accelerate... just... not very much.
You need bigger hills. Come down over the Pacific Divide some time, and
you can brake to 5MPH and be up over 80 MPH in half a mile.
--
Darren New / San Diego, CA, USA (PST)
Helpful housekeeping hints:
Check your feather pillows for holes
before putting them in the washing machine.
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> Oh, it *does* accelerate... just... not very much. I mean, if you point a
> *bicycle* downhill, it takes off like a rocket. And it doesn't even weigh
> much! But a much heaveir car... doesn't seem to pick up speed very much.
If there was no friction the car and the bike would accelerate at the same
rate, however cars have a lot more friction in the wheel bearings, tyres etc
because they are heavier by a factor of like 20.
BTW did you actually try the experiment or is it just what you imagine? It
feels a lot faster doing 30mph on a bike than 30mph in a car!
>> Ermm, my car moves just by lifting the clutch gently, no need to rev at
>> all.
>
> Is your car diesel by any chance?
Yes, but even petrol cars can do this - you just can't lift the clutch as
quickly because the flywheel is usually much lighter in petrol cars. Try
it - you only need to give it some revs if you want to move off relatively
quickly.
> Right. So given that there's roughly 10^3 revolutions per minute, that
> would be about 10^(-3) L per minute. ;-)
Still not right, you can't use 1 mL of fuel per minute at 75 mph, otherwise
you'd be able to drive for 5 weeks continuously without refilling! Using
something like 100-150 mL/min of fuel seems much more likely for a normal
car at 75 mph.
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