In article , Dave Plowman (News) scribeth thus
Hrump!, The car under discussion wouldn't get me to the main Two London airports and its very marginal if it could do a return trip to the nearest one!..
most car losses are tyre rolling resistance and air resistance. Neither of which I would describe as friction, though that;s more a matter of precise definition.
So that's how to improve the range of any car - get rid of the tyres. And of course drive very slowly where air resistance is minimal. Or drive with the wind where it helps things.
It's the major factor. In still water a single person can move a ship weighing many tons. You'll not do that with a similar weight vehicle.
Trains have much less rolling resistance as do bicycles with very small high pressure tyres.
And
Absolutely. an electric bicycle is far better than a car in terms of miles/Kwh..
Due to the tyre rolling resistance.
I can in fact push a van weighing several toinnes on well pumped up tyres on a dead smooth flat road.
remember that what you BELIEVE is not the truth, necessarily. Its what you believe, that's all.
Measuring the effects of things independently is the key to getting an accurate understanding, not relying on religion.
I'm talking about a small ship like say a trawler where I've seen it done.
I'll bet you'll not move a truck weighing anywhere near as much.
As I said, that's because of the tyres.
Whether you call that friction is up to you. Personally I dont. Friction to me is sliding contact between hard surfaces, or fluid over a surface.
If you did in fact have a classic frictional case as a boat hull in water, you very quickly find that cars go faster than boats of the same weight for the same power
Tyre rolling resistance represents almost a fixed drag component irrespective of speed.
Boat hull resistance is purely a function of wetted area and speed.
Air resistance is more complex, because air is more compressible. Its a function of frontal area and shape.
You only need to look at how much load a single horse could pull on a canal barge.
Indeed, but it does NOT support his thesis that its 'friction'
but if it wasn't for friction, the wheels would simply spin on the ground.
T'aint necessarily so. The non-flatness at a macro scale would be sufficient without any 'real' friction being needed.
that's not what slows you down. Friction between surfaces that are not moving relative to one another wastes no power.
In message , The Natural Philosopher writes
A displacement boat has a "natural" maximum speed (the hull speed) dependent on the hull length. I've often wondered if something similar applies to cars in air.
It might explain why in the old Omega, fuel consumption on the motorway only went skywards over 70, but my current vehicle is bad over 60.
But they are moving relative to one another, all the time.
A helluva lot to do with overall gearing and torque characteristics of the engine, too.
not at the pint of contact. That's the whole point
Unless you are in a wheelspin mode
hardly likely if you are towing or pushing a van.
That depends. At very low speed the friction of a floating object is negligible; that isn't true of a car. I'll happily push a 10 tonne boat off from a jetty, but I wouldn't even try with a truck.
I see you don't sail much.
... and you won't notice the compressibility of air until you get to a substantial fraction of the speed of sound.
Andy
Stick a bulbous prow on it and see what happens ...
Hull speed is when you are travelling at about the same speed as a wave of the same length. Increase speed and your stern wave falls behind, so you are climbing a wave at the front but not getting pushed by the stern wave behind - and power needed goes up.
In a car air resistance is proportional to the square of the speed. (and power to the cube). So go faster, use much more fuel. And you get odd effects in engine efficiency too - petrol engines are really inefficient at low power settings, so go a little faster and you may get better fuel economy especially on a large petrol engine. I'm guessing the Omega wasn't a diesel? And that the current car has a smaller engine?
Andy
Au contraire getting a boat to plane is about getting the wetted area down
I see you dont do physics or aeronautics. OR have a car with tyres that are inflated.
ISTR many years ago someone put forward a figure of 2hp needed to move a pair of wing mirrors at 70mph.
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