Things you always wanted to know the answer to [Vol. 4]

[ajprice]

SpeckledJim said:

Those bottom ones are perhaps even worse in terms of pedestrian impact than the original popups.

It was a random google image, there are other setups with fixed lights under glass.

[gothatway]

Flibble said:

Shakermaker said:

And surely pop up headlights could be made safe but still look cool?

Someone needs to engineer a way to do this

It's aerodynamics as well as safety that put paid to them. Who is going to take the efficiency loss of them?

An interesting report on the 944's aerodynamics. Summary : a 6% increase in drag with the lights up. The report states that the last new cars with pop-up headlights were in 2004.

[Shakermaker]

gothatway said:

Flibble said:

Shakermaker said:

And surely pop up headlights could be made safe but still look cool?

Someone needs to engineer a way to do this

It's aerodynamics as well as safety that put paid to them. Who is going to take the efficiency loss of them?

An interesting report on the 944's aerodynamics. Summary : a 6% increase in drag with the lights up. The report states that the last new cars with pop-up headlights were in 2004.

6% increase in drag, 600% increase in cool.

Worth it

[glazbagun]

Something I once knew but now can't remember. Does temperature bleed out at a constant rate?

For example, if I have some hot black tea and some room temperature milk, then it doesn't matter when I add the milk, the mixture will always take the same time to reach ambient temperature, (ignoring the tea heating the room here) correct?

[SpeckledJim]

glazbagun said:

Something I once knew but now can't remember. Does temperature bleed out at a constant rate?

For example, if I have some hot black tea and some room temperature milk, then it doesn't matter when I add the milk, the mixture will always take the same time to reach ambient temperature, (ignoring the tea heating the room here) correct?

I don't know the answer to this, but my hunch is that the time taken to lose 1 degree is shorter when the tea is very hot than when it is merely warm.

So left to its own devices your tea goes from 90 degrees to 80 degrees more quickly than it goes from 50 degrees to 40 degrees.

So I think that means that adding the milk earlier will give you a marginally longer-lasting drinkable cuppa. Just a guess.

[Allan L]

SpeckledJim said:

glazbagun said:

Something I once knew but now can't remember. Does temperature bleed out at a constant rate?

For example, if I have some hot black tea and some room temperature milk, then it doesn't matter when I add the milk, the mixture will always take the same time to reach ambient temperature, (ignoring the tea heating the room here) correct?

I don't know the answer to this, but my hunch is that the time taken to lose 1 degree is shorter when the tea is very hot than when it is merely warm.

So left to its own devices your tea goes from 90 degrees to 80 degrees more quickly than it goes from 50 degrees to 40 degrees.

So I think that means that adding the milk earlier will give you a marginally longer-lasting drinkable cuppa. Just a guess.

1950s O level physics taught us that heat transfer rate is proportional to temperature difference, so SpeckledJim is quite right in his first two statements but the third confuses me.

[SpeckledJim]

Allan L said:

SpeckledJim said:

glazbagun said:

Something I once knew but now can't remember. Does temperature bleed out at a constant rate?

For example, if I have some hot black tea and some room temperature milk, then it doesn't matter when I add the milk, the mixture will always take the same time to reach ambient temperature, (ignoring the tea heating the room here) correct?

I don't know the answer to this, but my hunch is that the time taken to lose 1 degree is shorter when the tea is very hot than when it is merely warm.

So left to its own devices your tea goes from 90 degrees to 80 degrees more quickly than it goes from 50 degrees to 40 degrees.

So I think that means that adding the milk earlier will give you a marginally longer-lasting drinkable cuppa. Just a guess.

1950s O level physics taught us that heat transfer rate is proportional to temperature difference, so SpeckledJim is quite right in his first two statements but the third confuses me.

Me too!

My guess was that adding the milk early takes the tea into a lower temperature quickly, but raises its thermal mass, so it's (marginally) better to have a higher mass at a lower temperature, than a smaller mass at a higher temperature, because higher temperatures are relatively fleeting.

This may be bobbins.

[Clockwork Cupcake]

Allan L said:

1950s O level physics taught us that heat transfer rate is proportional to temperature difference

My 1980's O-level physics agrees with you.

[MartG]

Clockwork Cupcake said:

Allan L said:

1950s O level physics taught us that heat transfer rate is proportional to temperature difference

My 1980's O-level physics agrees with you.

Proportional to the fourth power of the temp difference IIRC

[Shakermaker]

Clockwork Cupcake said:

Allan L said:

1950s O level physics taught us that heat transfer rate is proportional to temperature difference

My 1980's O-level physics agrees with you.

And it all disproves the idea that used to float around at some point that "Hot water freezes faster than cold water"

I definitely remember being told that as a child

[SpeckledJim]

Shakermaker said:

Clockwork Cupcake said:

Allan L said:

1950s O level physics taught us that heat transfer rate is proportional to temperature difference

My 1980's O-level physics agrees with you.

And it all disproves the idea that used to float around at some point that "Hot water freezes faster than cold water"

I definitely remember being told that as a child

Can of worms time...

I think that this is actually a thing. Under circumstances I don't understand, for reasons I don't understand.

ETA: the Mpemba Effect. Which I don't understand.

[Clockwork Cupcake]

Certainly on QI they showed that hot water being poured into a glass sounds different to cold water being poured into a glass. Something to do with hot water being more "slippy" due to the extra energy in it.

[Europa1]

SpeckledJim said:

Shakermaker said:

Clockwork Cupcake said:

Allan L said:

1950s O level physics taught us that heat transfer rate is proportional to temperature difference

My 1980's O-level physics agrees with you.

And it all disproves the idea that used to float around at some point that "Hot water freezes faster than cold water"

I definitely remember being told that as a child

Can of worms time...

I think that this is actually a thing. Under circumstances I don't understand, for reasons I don't understand.

ETA: the Mpemba Effect. Which I don't understand.

A mate of mine used to work for the British Antarctic Survey and said he'd tried it, and yes, it can be "a thing".

[98elise]

SpeckledJim said:

Shakermaker said:

Clockwork Cupcake said:

Allan L said:

1950s O level physics taught us that heat transfer rate is proportional to temperature difference

My 1980's O-level physics agrees with you.

And it all disproves the idea that used to float around at some point that "Hot water freezes faster than cold water"

I definitely remember being told that as a child

Can of worms time...

I think that this is actually a thing. Under circumstances I don't understand, for reasons I don't understand.

ETA: the Mpemba Effect. Which I don't understand.

It can happen in very particular circumstances, however 99.99% of the time cold water will freeze quicker than hot water and our faith in O Level physics is restored.

[ajprice]

Is this the same O level physics that makes ice cubes from boiled water clear?

[Flibble]

Clockwork Cupcake said:

Certainly on QI they showed that hot water being poured into a glass sounds different to cold water being poured into a glass. Something to do with hot water being more "slippy" due to the extra energy in it.

Dunno about "slippy" but the difference in pitch is because hot water has let viscosity,much like many things when they are hot (oil, syrup etc).

[227bhp]

How do I put a degree symbol (the tiny o thing) into a post or an email? How do I get a normal keyboard to do this?

Edited by 227bhp on Saturday 9th March 09:30

[227bhp]

On the topic of hot frozen tea:

[MartG]

ajprice said:

Is this the same O level physics that makes ice cubes from boiled water clear?

Isn't that because boiling expels any dissolved gases ?

[Clockwork Cupcake]

227bhp said:

How do I put a degree symbol (the tiny o thing) into a post or an email? How do I get a normal keyboard to do this?

On Windows, you hold down the Alt key, type 248 on the numeric keypad, then release the Alt key.