i don't care if you win by an inch or a mile
I'll start this post off with a video.
Just some random things:
I have been driving lots and I've been wondering about brakes and brake pads. If you apply the brakes lightly and take a long distance to slow down, does that wear the pads more or less if you applied the brakes hard and took a short distance to slow down? It could be a relationship, like Brake Force is directly proportional to Brake Pad Wear and indirectly proportional to Stopping Distance. Of course, this doesn't take into account the other factors such as tire grip and friction of the moving parts in the car. I just wonder because people always say to slow down lightly, but is there really a benefit in terms of brake pad wear?
Stop first, go first. 'Nuff said. I don't care if you are going straight and I am turning left.
Just some random things:
I have been driving lots and I've been wondering about brakes and brake pads. If you apply the brakes lightly and take a long distance to slow down, does that wear the pads more or less if you applied the brakes hard and took a short distance to slow down? It could be a relationship, like Brake Force is directly proportional to Brake Pad Wear and indirectly proportional to Stopping Distance. Of course, this doesn't take into account the other factors such as tire grip and friction of the moving parts in the car. I just wonder because people always say to slow down lightly, but is there really a benefit in terms of brake pad wear?
Stop first, go first. 'Nuff said. I don't care if you are going straight and I am turning left.
posted by ed @ 5:44 PM
2 Comments:
At 7:14 AM, August 16, 2006,
Matt Lam said…
Hmm, bored at work, so I decided to think about your braking question in a little more depth. I made a few simplifying assumptions (That the wheels roll without slipping throughout, and that the car is essentially a point mass so I don't have to worry about rigid-body interactions). I applied dimensional analysis:
So let's suppose that the problem is defined by, oh I don't know, 6 variables: the wear of the pads (W), stopping distance (d), braking force (F), the shear modulus of the pad material (s), the mass of the car (M), and the moment of inertia of the wheel (I). By the Buckingham Pi Theorem, selecting mass, length and time as fundamental variables we would need 3 dimensionless parameters to describe the system... after a little bit of work I found these to be P1=sWd/F, P2=I/Md^2, and P3=FM/sI. Now to get a straighter answer it will get a little dicey:
With those groups we can say that the stopping distance d depends on some function F(P1,P2,P3). Not very interesting unless you're going to run experiments so we'll have to simplify a little bit more.
s is really big (it's measured in GPa) so I will say that P1 >> P3. Also since the car is more massive than a wheel, P2 is small also so we can say that it's more or less a function of P1 only. That is, sWd/F is dimensionless. In other words,
W = F/ds
or brake pad wear is directly proportional to the braking force, and inversely proportional to braking distance and strength of the brake pad material, just as intuition would suggest. If we put in crazy values for stuff it all makes sense too: If we have an infinitely strong brake pad, there is no wear...if we brake instantaneously (which is impossible), the wear would be infinite (which is impossible, which is consistent with the real world) and if you're not braking (F=0), you have no wear. Pretty cool, eh?
...okay, well not really cool. But gimme a break, I'm bored at work waiting for a measurement to finish...
At 9:53 AM, August 16, 2006,
ed said…
Sweet! That's cool. I'll think of more physics problems for you Matt.
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