/sci/ - Science & Math

>>11051128
No, it's correct for the reason stated in the image

>>11051144
The speed at which those blocks accelerate down the ramp is purely a function of the ramp’s incline, the block’s weight, and the coefficient of friction.

Right?

>>11051128
If they're equal weight and made of the same material, (i.e. equal density) that implies that they have equal volume. Note that box a is taller than box b. Therefore box A would actually have less surface area in contact with the ramp. (Think 3-dimensionally)

>>11051128
>no center of gravity shown
yikes

>>11051128
>what gases are in the box?
oof

>>11051128
source of this image anon?

>>11051147
The net frictional force on both boxes is the exact same, it’s independent of surface contact. If they have the same weight on the same incline, they have identical normal forces acting on them from the ramp, and if they are the same material they will have the same friction force acting on them, and therefore the same acceleration down the ramp.

>>11051166
https://www.albanyny.gov/Libraries/HR-_Job_Postings/MechanicalGuide.sflb.ashx

>>11051170
then why are ice skates made so thin?

>>11051192
Maximize point pressure to melt the ice to water reducing the coefficient of friction.

>>11051128
Friction force should be independent of contact area. If B is correct it is only because that box is about to tip over.

>>11051231
then why are car racing slicks made so wide?

>>11051256
Because the road isn't a uniform homogeneous surface and you need a wide tire to find grip where it is available..

>>11051265
probably distributes heat and wear better too

It's the same, frictional force = (mu)(normal force)

>>11051383
Only under ideal conditions (no deformation of the box material). But.. Being that this image gives no such information, it's either both the same or B. I don't think there's a way for A to slide faster.

>>11051147
Maybe the friction surface is the same material but the rest of the box isn't. Volume wouldn't HAVE to be identical. Could be hollow boxes with different wall thicknesses as well, which doesn't condradict anything in the image.

>>11051395
Why would you assume deformation of the box material?

>>11051128

It is wrong. They are morons.

the only thing that matters is the normal force of gravity and the coefficient of sliding friction.

in real world applications the increased surface area would dissipate heat faster and therefore the coefficient of sliding friction would not increase (as most do when heated) which would mean over time A would go faster then B, but the surface area has nothing to do with sliding friction.

How can they have the same weight and same material and different sizes?

>>11051519

>>11051147
>that implies that they have equal volume
It could be hollow on the inside lmao
always knew you were a moron

>>11051170
wrong

>>11051519
Hollow
O
L
L
O
W

>>11051442
Deformed by the force of friction.
How do you think tires work?

Box B looks like it might topple. A will slide gently down

A

>>11051256
A lecturer once suggested that the rubber, under the pressure of the cars weight + the heat of the work being done, converts to a viscous liquid on the surface.
Frictions involving liquid/solids depend on surface areas unlike solid/solid interactions, and so wider slicks work better.
No idea how valid this is.

>>11051128
It's wrong, all right. Kinetic friction has nothing to do with surface area.

>>11051383
>>11051146
Box A has a higher coefficient of friction

>>11052893
>Box A has a higher coefficient of friction
Why do you think that this is true.

>>11051128
>This is wrong, isn’t it?
Yes it is. All forces on the boxes are identical.

>>11052893
>Box A has a higher coefficient of friction
no it doesnt. friction coefficient is a function of the material only. it has nothing to do with surface area.

>>11051864
This. But I was more pointing out that lack of information either makes us assume the simplest answer (both move equally easily) or assume real world conditions (B moves easier). Regardless of which reasonable assumptions you make, A is not easier to move.

>>11052950
>assume real world conditions (B moves easier)
Why tho?

>>11051128
>Amontons' Second Law: The force of friction is independent of the apparent area of contact.
But this is only an approximate law. So the question is, in what direction does it deviate? It seems perfectly possible to me that there are interfaces that violate the friction equation in both directions:
1) as surface area increases, the area of surface interaction increases
2) as surface area decreases, pressure increases, and so does the interaction per unit area of the two surfaces

But it also seems reasonable that in the case of a rigid, chemically inert surface, 1) would dominate

>>11053222
(and in some cases, e.g. ice skates, pressure may have the effect of reducing friction)

>>11053222
>But it also seems reasonable that in the case of a rigid, chemically inert surface, 1) would dominate
Why tho?

>>11053269
Here's a model to imagine: Say two square toothed surfaces fit into each other exactly. more pressure after a certain point doesn't make a difference because the surfaces are flush. Theonly way to push these surfaces past each other is to deform these teeth. This is a material property unrelated to the pressure (assuming the pressure is light). As the surface area increases, the number of teeth you need to deform increases, so the friction increases.

>>11053292
But the two surfaces aren't square teeth.

>>11051128
They will slide down with equal ease. They have the same weight and have the same surface roughness. Pressure per unit area will be lower for the big box, but due to larger area, the integrated pressure over the area is the same as that of the small box. This pressure, combined with the "roughness" aforementioned, lead to friction forces. This friction force will be the same for the two boxes.

>>11051256
To maximise the contact area with the ground for maximum grip

>>11053299
one thing where friction scales with surface area as I describe: velcro

>>11053405
Except that's not true at all because Velcro doesn't follow the rules of friction force. It's more like an adhesive because it resists movement even with no normal force applied.

>>11053451
>velcro doesn't follow the rules
That's exactly the point. friction is resistance to motion, it doesn't need to relate to normal force at all.

Also: if you cover two surfaces with paired velcro, you will find that normal force does indeed affect the observed friction force

>>11053465
>it doesn't need to relate to normal force at all

Except that's absolutely fucking wrong.

>>11053486
>Friction, n. The rubbing of one object or surface against another.
I'm not really interested in your trolling anymore.

>>11053494
How do you rub things together without a normal force retard.

>>11053508
Eddy currents, for one

>>11053513

Some say it's wrong, some say it's right; /sci/ is useless as always in this matters

even considering deformities you'd guess A since B exerts a greater pressure...

moments u ruffled cunts

It depends on the weight, and how strong the ramp is.

If the box is just heavy enough to bend the ramp backwards in the case of B, then A will not bend the ramp as much, since the weight is more evenly distributed.

Thus, A will slide down the ramp faster.
In fact, B might even be stationary if the ramp is bent back far enough.

>>11051519
why is your head so light?

>>11051128
>talks about friction
>doesn't mention coefficient of static friction
>doesn't mention coefficient of dynamic friction

>>11052945
the coefficient is the same
now look up what a coefficient is