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This whole debate is going over my head (and I suspect a lot of other peoples too)
Oh dear.
I'm sorry, its me trying to understand why jikovron thinks that two pistons each supplying a force only give the same force as one. That and to explain, why ever it is he thinks that, he's wrong. It is absolutely certain that you have two pistons each pressing on something with 1N, the total force on whatever they are pressing on is 2N. And in that specific issue, it don't matter if they press on the same or opposite sides.
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Would someone like to explain (in words of one syllable preferably) what "force" is in this context and what (if any) are the differences between "force" and "energy"?
Again, oh dear.
Force can be described simply as a push or a pull. The SI unit is the Newton, and its that amount of push that will accelerate (where there are no other forces like friction or drag) a mass of 1kg at a rate of one meter per second per second: one meter per second squared. That is, a force of 1N increases the speed of something with a mass of 1kg by 1m/s in every second. So, because Earths gravity causes an acceleration of 9.81 meters per second squared, the force downward from a mass of 1 kg on the surface of the Earth or anything fixed and parallel to it, is 9.81 Newtons. We should then talk about the weight of things being in Newtons, but being humans and easily confused, we still use kilograms.
The simplest definition of energy is "the ability to do work". Energy is how things change and move. The SI unit is the Joule, and its where a force of 1 Newton moves its point of application by a distance of one meter.
As a free extra, power is the rate at which work is done. The SI unit is the Watt, and its 1 Joule per second, so where a force of 1 Newton moves its point of application by 1 meter in one second.
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What little I remember of O level physics, says energy may not be created or destroyed, it just gets moved around or stored. What you get out is what you put in (minus parasitic losses from gravity, friction, inefficiency or whatever)
True enough, but not relevant to this. Which is really all about force and reactions.
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Apply this idea to a braking system and you are putting energy into a caliper by applying pressure to a hydraulic system. Assume for the sake of argument you are putting 1 unit of energy into your caliper, this is then divided equally between 2 pistons whether by separate feeds to each piston WITHIN the caliper (fixed caliper) or by pressurizing the piston and caliper body (floating caliper) Either way there is only 1 unit of energy to go round so each piston (or pseudo piston) gets 0.5 units of energy each.
Now take the single seized piston in a 2 piston fixed caliper. both pistons still get the 0.5 units each, but, because the piston is seized, the energy is contained and doesn't reach the pad. Most of this energy, I suspect will feed back to the other piston which WILL move and transfer itself through bending the disc and the bearing till it meets the other, now fixed, pad. Still 1 unit of energy used, just a load of parasitic losses from bending the disc and bearing. Then the whole lot gets dissipated through the disc and pad as heat energy to atmosphere, not lost or destroyed energy, just given away! Just a lot less efficiently than if both pistons were free.
So explain to the idiot (me) how you can put 1n in at the hose connection and get 2n out, 1n at each piston?
Steve
The answer to all of that, and especially the last line, is hydraulics. It's all about the pressure in the fluid and the cross sectional area of the master and slave cylinders. Pressure is in Newtons per square meter (SI unit of pressure is the Pascal, which is 1N/sq.m). So you put in a hydraulic pressure of 1 Pascal and every meter squared that fluid touches is pushed by 1N of force. The important bits are the the pistons in the master and slaves. But Pascals are too small to be of any blumin use, and everybody uses the kilo Pascal (kPa)
So (using easy, but not necessarily representative numbers), if you apply 100N of force - equivalent to the weight of a 10.2kg mass - to a master cylinder of 1/100th of a square meter, you get 10kPa of pressure. If you and apply that hydraulic pressure to a slave cylinder with a piston of 1/10th of a square meter in area, you get 1000N or ten times as much force from the piston as you put on the pedal. Do remember that area goes with the square of diameter. However (ignoring how the hoses swell) the pedal has to move ten times as far as the piston. It's as well to go look at how a hydraulic lift works to grasp Pascals principle. It may be hard to see, but its exactly like a lever: If the distance from fulcrum to input (your arm) is ten times that from fulcrum to load, there's ten times the force you put in at the input applied to the load, but if you actually move the load, the input has to travel ten times as far. Technically, that's where the energy is, the pedal force being one tenth of the piston force but moving ten times as far give the same energy out as you put in.
So, at 10kPa of hydraulic pressure, every piston of 1/10 sq.m gives 1000 Newton or force. But, every time you multiply the number of pistons, if they all have to travel the same difference, the pedal has to travel the same number of times further.
So, if one piston is seized, and you press with the same force on the pedal then the one(s) that still work still give the same ten times as much force, i.e. 1000N, out. But, because one of the pistons doesn't move, the pedal has to move less, and energy out is still the same as the energy in. The important bit is that the ones that are not seized do not give more force out for the same force on the pedal because one has seized. And it's the force on the pad that determines how quick you stop (with the distance from pad to hub centre and the coefficient of friction between pad and disc, but according to Ammontons not, in any situation, the area of the pad).
I doubt that cleared much mud though.
Graham