- #1
mehgon
- 1
- 0
Two trucks with the same futures,one loaded and one empty. They are traveling on same speed and when they brake on the same spot;which one stops earlier? Does a truck's load affect it's braking distance?
Thanks..
Thanks..
The relevant force is the one that the road can apply.newjerseyrunner said:The force that the breaks can apply does not change regardless of the size of the truck.
If it slides, which the OP doesn't specify.newjerseyrunner said:Okay, the amount of force applied to the truck is the force of kinetic friction.
So assuming sliding with the same friction coefficient, and ignoring all other retarding forces, what is the answer?newjerseyrunner said:The friction coefficient times the normal force.
That's only true if the brakes are good enough to cause wheel slippage. Plenty of 'old' vehicles had the sort of brakes that would never cause a skid on a decent road surface. Under those conditions, the braking force could be considered independent of load (strength of the driver's right leg, in fact). But even if the limit is when the wheels slip, you can't treat the tyre / road friction as linear (not a constant coefficient of friction) so that makes good theory based predictions pretty difficult. With suitable choice of tyre and surface, I reckon you could get any answer you wanted to the OP.A.T. said:The relevant force is the one that the road can apply.
A.T. said:The relevant force is the one that the road can apply.
sophiecentaur said:That's only true if the brakes are good enough to cause wheel slippage.
Are you saying that the torque that is present in the brakes plays no part in the braking process? You can't be!A.T. said:It's always true. Only external forces can slow down the truck.
Which isn't specified.sophiecentaur said:If there is no skidding
I dealt with both eventualities. You could even assume ABS. I think you have to admit that the majority of times that vehicles stop does not involve skidding.A.T. said:Which isn't specified.
My statement in post #4 also applies in both cases.sophiecentaur said:I dealt with both eventualities.
That statement is actually wrong unless the wheels are slipping. In most circumstances the force is less than the limiting friction force between road and tyre. Can you possibly argue otherwise?A.T. said:My statement in post #4 also applies in both cases.
What is wrong about saying that only external forces can accelerate an object? That is true regardless of slipping or not.sophiecentaur said:That statement is actually wrong unless the wheels are slipping.
Nothing wrong with that. What is wrong is to associate that with the braking distance / mass relationship. The braking force is nearly always less than the limiting force on the tyres (which is proportional to the mass, where the simple basic law of friction applies). Mostly, the braking force is governed by the forces on the brake discs - which is independent of the mass. So the braking distance will be dependent on mass (surprise surprise).A.T. said:What is wrong about saying that only external forces can accelerate an object? That is true regardless of slipping or not.
sophiecentaur said:majority of times
sophiecentaur said:In most circumstances
I don't think questions like this want you to consider the infinite number of possible sub-optimal circumstances. The most reasonable way to compare the two braking situations is to assume optimal braking strategy in both cases, with the maximal ground friction possible in each case. Otherwise the answer becomes arbitrary.sophiecentaur said:nearly always
I realize you don't want to let this go but most trucks, when brought to a halt on most occasions, do not skid. (That's not one of any 'infinite' set of circumstances; it's the majority.) To my mind, it is not an unreasonable situation to consider. You mention "optimal braking strategy". Doesn't that imply non skidding? That implies that the wheels are not locked and that the braking force is a function of the brakes.A.T. said:I don't think questions like this want you to consider the infinite number of possible sub-optimal circumstances. The most reasonable way to compare the two braking situations is to assume optimal braking strategy in both cases, with the maximal ground friction possible in each case. Otherwise the answer becomes arbitrary.
It implies maximally possible friction force, which is usually a function of normal force and static friction coefficient.sophiecentaur said:You mention "optimal braking strategy". Doesn't that imply non skidding?
The maximally possible external braking force, is limited by normal force and static friction coefficient. So there is no need to consider some internal forces to determine the minimally possible braking distance here.sophiecentaur said:That implies that the wheels are not locked and that the braking force is a function of the brakes.
I see our mutual problem now. At the point of slipping and assuming that the friction coefficient is constant for all loads (we can't improve on that without knowing more) the friction force F will be proportional to the mass / weight but the braking acceleration will be proportional to F/ mass, which is independent of mass. In real life, the force from the brakes is always adjusted to avoid skidding and the force applied to the brakes will be limited to the force on the pedal, which is very relevant when answering the question "Is the braking distance affected by mass?"A.T. said:It implies maximally possible friction force, which is usually a function of normal force and static friction coefficient.The maximally possible external braking force, is limited by normal force and static friction coefficient. So there is no need to consider some internal forces to determine the minimally possible braking distance here.
In my experience, without ABS, the tires of a passenger car will lock up with far less than maximum force applied to the pedal. With ABS, they will start pulsing with far less than maximum force. I've never had the brakes fade so badly that it was not possible to lock up the tires.sophiecentaur said:I have frequently been pressing as hard as possible on the brakes of a car with no servo assist and been all too aware of the fact that there were four passengers in it and an obstacle not very far in front.
If you want to answer this based on real life, not on an idealized model, then It's almost trivially true that the load will have some effect.sophiecentaur said:In real life...
Yes. That has to be true. It's in the UK Highway Code, based on experience and evidence. But a good explanation for it has not been proposed in this thread (except mine ).A.T. said:If you want to answer this based on real life, not on an idealized model, then It's almost trivially true that the load will have some effect.
Yes. A truck is very unlike a block of wood on a lab bench and many of the comments on this thread have been assuming they are very similar.Lok said:Of course a heavier truck will brake in a longer distance.
The weight of a truck's load can significantly affect its braking distance. The heavier the load, the longer it will take for the truck to come to a complete stop. This is because the added weight increases the momentum of the truck, making it more difficult for the brakes to slow it down.
There is no specific weight limit that directly affects a truck's braking distance. However, the heavier the load, the longer the braking distance will be. Other factors such as speed, road conditions, and brake quality also play a role in a truck's braking distance.
The type of load can also affect a truck's braking distance. A load that is evenly distributed and secured properly will have less of an impact on the truck's braking distance compared to a load that is unbalanced or not properly secured. This is because an unbalanced load can cause the truck to sway, making it more difficult to control and stop.
Yes, the quality and condition of a truck's braking system can greatly affect its braking distance. A well-maintained and high-quality braking system will be more effective in stopping a truck, even with a heavy load. On the other hand, a faulty or worn-out braking system can significantly increase a truck's braking distance.
Yes, there are several other factors that can affect a truck's braking distance. These include the condition of the road (e.g. wet, icy, or uneven surfaces), the speed of the truck, and the driver's reaction time. It is important for truck drivers to be aware of these factors and adjust their driving accordingly to ensure safe braking distances.