shouldn't it float??

Nirav Chavda

if one recalls the old classical physics terms namely repose angle, i've got a problem for them.
as it(repose angle) is meant for is a state when a matter lying on an inclined plane with a repose angle to ground ... then there will be equilibrium between the frictional and gravitational force.... so in such case why does the mass slide down instead of floating? and that too with "SOME" CONSTANT speed?
as far as i think .. it should be floating..
any help there? thanks

brewnog

Could you elaborate on that please?

Doc Al

What do you mean by "floating"?

If the mass is initially at rest, and the static friction is sufficient to balance the component of the weight acting down the plane, then the mass will remain in place.

Nirav Chavda

my friend but then it is not expected to remain there
as observed it would start sliding down
but the question that kicks me the most is why does it slide down with CONSTANT SPEED?
point to be noted - even though the gravitaional and frictional force are supposed to be same mathematically in this state ... motion is observed along the gravitational direction ... why?

Nirav Chavda

what i simply mean by floating is that the mass in that state will have net zero force acting on it (air friction can be considered nil) so it should either simply remain there or start moving randomly on the plane.

Doc Al

A mass with zero net force does not "start moving randomly". If its initial speed is zero, it remains zero. If it's moving (in which case it's kinetic friction that matters) then it will remain moving at constant speed.

HallsofIvy

No, that's not correct. The object will have a force of gravity straight downward. The "supporting" force (without friction) is perpendicular to the inclined plane. They do not "cancel" and the net force is not zero.

mukundpa

The gravitational force and the frictional force are not balancing each other. The friction is tangential to the plane, while the gravity is vertical. Friend you have forgotten the normal reaction. Is it?

Nirav Chavda

but then how will you explain the sliding down of that matter where the initial speed is zero.

Nirav Chavda

i didn't get you when you said not balanced.
i'm talkin about the gravity acting along the plane.

mukundpa

that is the component of the weight tangential to the plane, what about the other component normal to the plane?

Nirav Chavda

you are not getting my point.. i'm speaking of the active gravity ie- gravity acting along the plane (inclined downwards )
at repose angle they ARE equal and thats what repose angle is meant for.

mukundpa

The normal compnent is pushing the body towards the plane and thus the plane is reacting and appling equal and opposite reaction which is called the normal reaction.

Doc Al

Please try to explain your question once again, clearly. Is there friction along the plane? Is the friction great enough to balance the component of gravity acting down the plane? If yes, then the mass is in equilibrium: it will NOT start moving down the plane.

Of course, if the friction is insufficient, there will be a net force on the mass acting down the plane. It will start moving. Where's the issue?

Nirav Chavda

just forget those normal forces as we just want the mass to float meaning it should move on the plane randomly or remain still.
here normal aren't required as we are stuck with the plane.

Doc Al

Understanding the role of normal force is crucial in understanding the behavior of the mass. All forces count. (It's the normal force that determines the maximum value of the friction force.)

Nirav Chavda

brother ... here is my question again-

a mass is placed on an rough inclined plane which has an angle = inverse tan(coefficient of linear frictional force)
in such case the gravity down the plane (inclined) and the limiting frictional force are balanced.

just tell me what will happen next?