On 05/10/2010 00:08, dennis@home wrote:


"Clive George" wrote in message
...
On 04/10/2010 22:11, dennis@home wrote:


"Rick Cavallaro" wrote in message
...

On Oct 4, 12:28 pm, "dennis@home" wrote:

have you worked out why it takes four times as long to stop a car
that is
going twice as fast yet.
You can use either formula to find out as the constant doesn't matter.

Asked an answered. You claimed it takes 4 times as long to stop a car
that's going 20 mph vs. one that's going 10 mph. My answer: no it
doesn't. A normal car will take twice as long.

And there we have the proof you don't understand energy.

For anyone that cares..

the brakes use friction to turn kinetic energy to heat
they have a maximum rate at which they can do this..

True, but that's not reached in any modern brake. That's one of the
reasons cars have ABS.

Balls.
Cars have anti lock brakes because most drivers can't cope with
difficult conditions and you are trying to deflect your inability to
understand simple physics yet again.

"one of the reasons".

so as a car travelling twice as fast has four times the energy it takes
four times as long to dissipate the heat in the brakes.

Therefore false.

So it takes four times as long to stop.

False.

A modern car brakes at a fairly constant force, limited by tyre grip.

For a car with cr@p tyre in the wet that might be true, but not any
decent car

Not true. The limiting factor for a single stop for any modern car will
be grip, not brakes. Show me evidence to the contrary if you have any.
Once you're racing or descending mountains, life gets hotter, but that's
not what we're talking about.

Oh I forget you don't do decent cars with proper suspension
and tyres over there.

Where is "over there"? What sort of car do you think I drive? You might
like to take a look at the address I use when posting to usenet and the
groups I read for a clue to some of that answer.

Its funny that something like a Jag can pull 1.3G braking

Cite.

while you
crappy cars only do about 0.8G,

Why are my "crappy cars" any different to yours?

They both use similat tyres

Cite.

so I guess
you don't push the pedal hard enough or you have cr@p brakes.
Don't ever get close to a European car as you will go up his arse if he
brakes.

I do try to avoid getting too close to people, but that's nothing to do
with then being European. Of course if I'm driving I'll tend to be as
close to a European car as you can get...

v = u + at, a is the same, one of u and v is zero, therefore twice the
speed = twice the time. Twice as long.

s = ut + 1/2 a*t*t
t is doubled, s is quadrubled, therefore four times the distance.

That's o-level physics isn't it?

Its primary school but the kids get it right unlike you.

Nope.