General Questions

  • Thread starter Thread starter Orion
  • 2,283 comments
  • 107,704 views
Status
Not open for further replies.
Am I right in thinking that if all the sea ice in the world melted that sea levels wouldn't change, because ice displaces the amount of sea water that it contains itself?
 
Yes.

But of course there's a lot of ice locked up on land too, which displaces nothing.
 
Yeah that's the thing I see alot of people thinking when it comes to ice melting, that it's all floating in the water so if it melts it won't do anything. They always seem to forget that there's ice on land too which if melts will raise water levels.
 
Yes it would, as it's part of the mass. (Presuming you are talking about sea ice and the part of it above the water-line).
 
Alex.
Cheers guys, It may have actually been ground speed, and we were flying at higher than 35k feet aswell:tup:
Click to expand...

If that speed was GPS-calculated, then it was definitely ground speed, and the jet stream will give an aircraft a good 120- to 150-mph kick in the rear.

Regarding the ice above the water displacement question, remember that ice is less dense than the water it froze out of (sort of why it floats in the first place, see?) so that part of the ice that's in the water is the volume of liquid that it froze out of. That would be why it weighs the same, the very definition of displacement of a floating object.

I suppose everybody saw the proposal somewhere for those people living near the ocean to periodically grab a bucket of seawater, take it home and pour it down the drain, right? To keep the sea level from rising? :dunce:
 
Last edited:
Here is a question.

I have recently started driving, and I was wondering about fuel consumption and how it relates to the accelerator.

For instance, say I was driving down a road doing 25mph in 4th gear. The car would obviously be sluggish because I would not have the revs to accelerate efficiently. If I kept the accelerator floored, as opposed to just enough to get the car accelerating, would I use more petrol?
 
If you floor the pedal it means your fully opening the throttle. And while you might not get much response as your engine is way out of it's power bracket, you'll still be using more petrol. That's my thought on it, though ECU's mght throw all sorts of curveballs into the equation.
 
In relation. I am right in thinking that 3,000 rpm in 1st isn't going to be use the same amount of fuel as 3,000 rpm in 4th? To do with gearing iirc.

Just trying to compare that to cycling, where I think it's easier to feel forces.

*hopes he doesn't get corrected.
 
It might use the same amount of fuel per unit of time, but that's not how we measure fuel economy in cars. It'll use less fuel at higher gear because each engine rotation takes the car further.

As for accelerating in a taller gear than you'd like to be in, it sort of depends, because sluggish acceleration at high throttle might very well use more fuel than downshifting for a shorter amount of time, and having better acceleration. On the other hand, accelerating too slowly (to "save gas") is less efficient as well, as you spend too much time in lower gears. If it takes you 3/4 of a mile to reach 45, you've gone an awfully long ways in first, second, and third gears, as opposed to brisker acceleration and then cruising that distance in top gear.

Some years ago BMW tested fuel efficiency in acceleration and found that about 3/4 throttle was best; the best compromise between full-performance guzzling versus sluggish time- (and fuel-) wasting.
 
magburner
Here is a question.

I have recently started driving, and I was wondering about fuel consumption and how it relates to the accelerator.

For instance, say I was driving down a road doing 25mph in 4th gear. The car would obviously be sluggish because I would not have the revs to accelerate efficiently. If I kept the accelerator floored, as opposed to just enough to get the car accelerating, would I use more petrol?
Click to expand...

You would use more petrol if you floored it. My dads car has a monitor that displays loads of fuel consumption info on it. And one is your mpg on a sort of bar graph at that instance in real time and I've used it before to get the mpg as low as possible, whilst driving on my own, because it is boring and slow! And I found that by getting up to a high gear and very very gently accelerating that I could keep the graph looking good. On a combined cycle, going through town at about 20mph-30mph with little traffic and out of town at about 60 mph I brought the normal litre/100km reading down from 7.4 to 6.3, which is kind of ok, but with the effort involved and the lack of driving fun I dont drive like that too often, espeicially not in my own car.
 
The trick is to always get to the lowest stable speed (in other words, it won't slow down or require extra throttle above a trickle to stay at the same speed) in the highest gear possible... as quickly as possible. Every second you spend accelerating wastes gas.

Usually, you want this to be between 60-80 km/h. Any faster than 80 km/h usually wastes gas due to aerodynamic drag and rolling resistance, and any slower means you're usually fighting frictional losses.

Of course, full throttle braps waste gas, too... I usually do light throttle / high-rpm acceleration, but according to many motoring wags and testers, moderate throttle / low- mid- rpms is more efficient.

Still, any rpm at which the motor is lugging is a gas wasting rpm... you're wasting gas to overcome drivetrain losses that you shouldn't really be fighting.
 
niky
Any faster than 80 km/h usually wastes gas due to aerodynamic drag and rolling resistance
Click to expand...
I don’t believe either of those are functions of acceleration.

[Edit]: Just realized the beginning of your sentence is speed, not acceleration, though the rest of your post is in reference to acceleration…
 
Last edited:
Basically, whatever gear it takes to maintain your chosen speed with the lightest amount of throttle is your most efficient bet. Around town at low speed, that may be 3rd or 4th, for the reasons niky suggests above. As traffic opens up that is more likely to be the taller gears. As several folks have said, a short burst of solid acceleration followed by low-throttle cruise is the best way to increase speed.

Try 3/4 throttle as suggested - you'll find it is only marginally slower than WOT, yet it uses much less fuel. And on the contrary, you'll have to hold the throttle open at 1/4 far longer to reach the speed you wish, which also increases consumption.
 
Thanks for the info guys, I kinda had a suspicion that I would be using more petrol, but I couldn't be sure.

My car (Vectra 1.8i SRi new model) has a display that calculates fuel consumption based on how i am driving the car at that moment in time. At first I thought that the display was not working correctly, because the distance displayed would vary greatly. It took me a while to realise that it had a kind of 'lead-in' delay. now I've figured it out, I have improved my fuel consumption slightly.

Lately, I have taken to accelerating up to the rev limit in first gear, because as I hit 6,000rpm, my car is travelling at close to 30mph (the legal limit for urban areas in the UK). I then quick shift into 4th, and the revs drop to around 1,500rpm. This is perfect for cruising around town, obviously that is, if there is sufficient road ahead and no potential dangers.

I've also noticed that If I drop to around 1,200rpm, the engine starts to shudder. I know that the car needs more revs than that for forth gear, but does that shuddering cause wear to the clutch plates?
 
magburner
Thanks for the info guys, I kinda had a suspicion that I would be using more petrol, but I couldn't be sure.

My car (Vectra 1.8i SRi new model) has a display that calculates fuel consumption based on how i am driving the car at that moment in time. At first I thought that the display was not working correctly, because the distance displayed would vary greatly. It took me a while to realise that it had a kind of 'lead-in' delay. now I've figured it out, I have improved my fuel consumption slightly.

Lately, I have taken to accelerating up to the rev limit in first gear, because as I hit 6,000rpm, my car is travelling at close to 30mph (the legal limit for urban areas in the UK). I then quick shift into 4th, and the revs drop to around 1,500rpm. This is perfect for cruising around town, obviously that is, if there is sufficient road ahead and no potential dangers.

I've also noticed that If I drop to around 1,200rpm, the engine starts to shudder. I know that the car needs more revs than that for forth gear, but does that shuddering cause wear to the clutch plates?
Click to expand...

I destroyed my clutch experimenting how slow I could go in 5th gear, the ECU was trying to squirt fuel in the fuel to stop be from stalling but I was braking to prevent it from accelrating the car. I got 12 mph but on the journey home the clutch was slipping something awful. It was a very stupid thing to do. around 500 quid to replace including labour, the clutch was on its way out anyway so it was no biggie in the end, but yes if the cars beggining to kangeroo shift down. its not going to do your clutch any good if you do that often and your not in control of your car either, it will eventually stall depending on how fast you are going and lossing brake pressure and power steering isn't ideal.

Then again I haven't been driving for too long either so I could be completely wrong
 
If the engine is shuddering, it's not good for anything... basically you're using up power to overcome the inertia of the drivetrain and probably ruining your clutch and flywheel.

Sorry if my post mixed acceleration and speed... but yeah, 80 km/h is in reference to speed... but it'll vary per vehicle... some newer vehicles, by a combination of gear ratios and aero, are efficient at 80 - 90 km/h, but in general, staying at the lowest rpms possible (without shuddering) at 60-80 will give you fantastic mileage.

Just tried eco-driving in the CR-V (5AT) on a trip into the city yesterday... damn tranny would hold 5th gear at 60 km/h (posted minimum) and scrub off speed at light throttle (though getting about 16-18 km/l, otherwise... 40mpgUS), and you can't manually select to lock it in 5th gear... so you have to stay at about 80 km/h (posted limit), getting only 14 km/l (33mpg). Not bad... though traffic brought my overall average down to 12.5 highway (29mpg) and 9.2 combined (22mpg). Neither the slowest on the road, nor the fastest... overtaking some guys, pulling aside for others... I'm betting I could hold it at 40mpg on a long trip if I had a manual transmission or at least manual control over the 4th-5th gear change.

Only issue with accelerating at 3/4ths throttle, it's not very comfortable for the passengers... but it's fun. :lol:
 
Last edited:
magburner
Here is a question.

I have recently started driving, and I was wondering about fuel consumption and how it relates to the accelerator.

For instance, say I was driving down a road doing 25mph in 4th gear. The car would obviously be sluggish because I would not have the revs to accelerate efficiently. If I kept the accelerator floored, as opposed to just enough to get the car accelerating, would I use more petrol?
Click to expand...

Hey magburner, for future reference, a question like this very much warrants its own thread. So don't hesitate to post outside this thread in the Ask GTPlanet! forum.

This goes for everyone really.
 
sn00pie
Hey magburner, for future reference, a question like this very much warrants its own thread. So don't hesitate to post outside this thread in the Ask GTPlanet! forum.
Click to expand...

Thanks pal. TBH, I was expecting a simple straight forward answer, I never thought that it would of gone into this much detail! 👍
 
I've been trying to figure out the difference between a Halberd and a Pollaxe and I came up with a theory is it right?

Pollaxes are hammers on the end of very long sticks

Halberds are axes on the end of very long sticks.
 
BayConRong
I've been trying to figure out the difference between a Halberd and a Pollaxe and I came up with a theory is it right?

Pollaxes are hammers on the end of very long sticks

Halberds are axes on the end of very long sticks.
Click to expand...

Dunno, much about them historically, but this kinda reminded me of my days playing AD&D!

I've done a quick scan of the net for you pal, these links might help you:

The Medieval Poleaxe

Halberd

If your interested in medieval weapons in general, follow this link to the home page, for more detailed information:

MyArmory.com

Hope this helps a little. 👍
 
Halberd would be consider a spear.... type weapon. The Kusarigama is a very unique weapon.
 
First Air-Con related question.

1. My car air-con now doesn't really blow out really cold air, it just kinda blows out air which is cooler than the 60C inside my car but that car is still unbearable on a hot day with the windows up and the A/C on the max level. Does that mean I need to get one of those re-gassing things, or is it related to a more interesting problem I have which is...

2. My front De-mister doesn't work. When I turn the knob to demist, I get the slightest trickle of air out of it and the rest just comes out from my front vents. Which doesn't really help de-mist the car. If I got my car re-gassed would that be an easy fix at the same time, cause I'm thinking maybe the knob is broken or something. Or is that something more evil
 
Stig.
What is the greatest drifting angle officially achieved in the D1GP?
Click to expand...
I don't think that anyone has achieved a drift angle officially because it would be too much to focus on during the competition but you would lack other things.
 
2 questions:

- Can you use liquid oxygen instead of normal air for car engines?

-Can 2 stars collide in space?
 
DustDriver
2 questions:
- Can you use liquid oxygen instead of normal air for car engines?
Click to expand...

I'd have thought that liquid oxygen would make any metal engine components it came in touch with potentially brittle. Which wouldn't be such a good thing.
 
Casio
First Air-Con related question.

1. My car air-con now doesn't really blow out really cold air, it just kinda blows out air which is cooler than the 60C inside my car...
Click to expand...

Yes, it probably needs a refrigerant charge. Which meeans it probably also needs a gasket or seal somewhere in the AC system.

2. My front De-mister doesn't work. When I turn the knob to demist, I get the slightest trickle of air out of it and the rest just comes out from my front vents.
Click to expand...

Partly that's because your AC needs a recharge. Chilling the air also removes moisture from it (that's why idling cars drip on a hot day) so most cars turn on the AC even in cold weather when you run the demister. If the AC is not chilling, then it's not removing the moisture.

As far as the air volume goes, I would imagine that there is a vacuum leak in the control system. Most of the HVAC valving is actuated by vacuum in response to where you set the controls. If it's a much older car with sliders, it may be a mechnical linkage that has a kink in it. Either way, it will probably require taking the dash apart.

DustDriver
- Can you use liquid oxygen instead of normal air for car engines?
Click to expand...

You theoretically could, but not for long. A pint of LOX supports enough combustion to vaporize 60 pounds of charcoal briquets in about 3 seconds, including the grill they were piled in, so I doubt you'd like the results.

-Can 2 stars collide in space?
Click to expand...

Yes, though they move at such a slow pace (on a galactic scale) that rather than an actual collision like a car accident, what happens is that the larger star's gravity shreds the other star and absorbs its mass long before their actual stellar bodies would have touched.
 
Status
Not open for further replies.

Latest Posts

Back