Regardless of type (disk or drum), your brakes work by pressing a
non-revolving material against a revolving material and, as a result,
converting (via friction) the energy from the revolving material into heat.
The harder the materials are pressed together, the greater the friction and,
as a result, the greater the rate of conversion - i.e., the more braking
force applied, the quicker you slow down the revolutions of the wheels, and
the hotter the brakes become.
The brakes are also designed to radiate the resulting heat into the
environment and, thus, allow the brakes to cool down quickly after they are
no longer being used. This is a very important part of their design because
the braking material used loses efficiency (reduced friction) with high
heat. Indeed, if the braking material gets too hot it can be permanently
damaged (it will glaze.)
No one here has suggested that the traction of the tires stops the car.
The basic physics you are overlooking is that the pads can only stop
the car if the tires are spinning. If you try to brake too fast the
tires will stop spinning and you will slide to a stop over a GREATER
distance than if you had not braked so fast as to lose traction. This
is why anti-lock brakes intentionally limit the amount of breaking your
pads produce when your wheels start to slide. So you see that even
though it is the pads which stop the car their maximum braking
potential is actually governed by the tire traction. Pads which are
able to reach this upper limit of friction for the entire duration it
takes to stop the car will all stop the car equally fast -- no matter
how much or little they cost.
'cept that you have forgotten about pedal effort. Plus, different
friction materials will act differently because no one uses brakes from
0 effort to maximum or upper limit. Pedal effort. Different friction
materials, different stopping rates. And different friction materials
means different costs.
The brakes slow the rotors, which slow the wheels. The tires, mounted
on the wheels, slow the vehicle due to friction created between the
tire surface and the road/driving surface.
If this is incorrect, please explain how the "pads" stop the vehicle.
It looks like William is right about this. It seems that under normal
circumstances braking is limited by static friction between the tires
and the road, not by sliding or static friction between the pad and the
rotor. The coefficient of static friction between the road and the tire
determines a maximum torque that the brakes should apply to the wheel.
It would seem that ABSes increase the frictional forces between pads and
rotors until the wheels lock, then they let off so that the wheels
_don't_ lock up. Any pads can produce enough friction to lock the
wheels, so it is the tire traction that matters. Unless of course the
brakes overheat and begin to fade. I guess it doesn't matter unless you
might have to hurry down a tall mountain.
Uh oh. I think I may have to retract some of the above ...
The amount of sliding frictional force that can be developed between pad
and rotor depends on the materials. The maximum sliding torque will
differ. In other words some pads may cause the brakes to lock up and
the tires to skid at lower torques than other pads. Any pads can lock
up the wheels, but the better pads can keep the wheels turning while
applying large torques.
Car manufacturer's prices are not lower simply because they purchase in
bulk. They are also lower because they are free from such notions as
the more expensive a pad is the safer it is.
I never said that you should avoid having your brakes checked. In fact
while trying to point out to you the seemingly obviously bad analogy
between brain surgery and pad replacement I said: "and if I wasn't
satisfied with the results I could take the brain [pads] into a
hospital [shop] to be reviewed and possibly redone." Most people have
their brakes checked by a mechanic every 6-12 months depending on state
during their inspection. Right before a yearly inspection is a good
time to change the pads if they are wearing thin. Amazingly, having
brand new pads makes them less likely to fail you for having your
headlights out of alignment - but that is a different story.
Hope this helps,
I got a connection error from google groups-beta and hit submit again
resulting in two posts at Jul 23, 5:51 pm and Jul 23, 5:52 pm. Please
put all responses in this thread and ignore the other thread.
Turn the computer off. Disconnect all of the cables and other
connections into the computer, including the telephone line connection
for the modem, the printer connection, the monitor connection, and
everything else. Also unplug the power connector from the PC. It's
important that nothing external to the computer be connected before you
start the upgrade so that nothing outside of the computer can provide
any kind of electrical current to the computer while you are working on
it. It's not getting electrocuted that's the concern, it's that some
tiny electrical charge might come in at the wrong time and destroy a
component. It's not uncommon for a computer to draw a little bit of
electrical current while it is plugged in, even when it has been
powered off, so that's why it's important to unplug the power
If you're not used to disconnecting everything then you'll want to at
least carefully note where each connection was attached. The first time
I did this, I used a short strip of masking tape to scribble a little
note for each connection and then I wrapped the tape around the cord
before I disconnected it. Each connection should only connect one way,
so there's no need to remember how the connection was oriented before
it was disconnected. But chances are you've got a nice little
collection of connections into your computer, so you don't want to be
looking at a confused pile of disconnected wires when you're done
installing the memory!
Set the computer in a nice comfortable work space (personally, I just
use the middle of the floor) and remove the computer case cover.
Read the rest at
Hope this helps,
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