Mechanical Engineering - Engineering Mechanics - Discussion

Just assume that when a body is lies on horizontal plane then it is not move without any external force because there is also a static friction and its value is high on horizontal surface so here the angle of plane surface is zero. But the angle of friction is high. As a plane is going to be achieve an inclination the angle of friction is decreases. And as the angle of friction or simply the friction will decreases the angle of plane is decreases and body will automatically moves downward. So here the angle of plane is higher than the angle of friction.

It is very simple.
If a body is kept on a horizontal plane (angle of the plane {x} =0)

Here the friction force will be maximum so the angle of friction {y} will also be maximum.
Now if we increase the angle "x" the plane becomes inclined.
Now the friction force starts to decrease because it starts to act opposite in the direction of the line of motion to prevent the motion so, the magnitude of friction gets decrease and the angle of friction will also get decrease.

That means;
Y > X = REST.
Y = X = IMPENDING MOTION.
Y < X = MOTION.

I think it should begin to move when the angle of inclination is equal to the angle of friction.

As the Angle of Repose is the angle of inclination in which the body begins to move itself.

And the angle of Repose is equal to the angle of Friction. Therefore it should equal to angle of friction.

Does anyone know why its "greater"?

@all.

A body on an inclined plane just tends to slide down if the angle of inclination is equal to the angle of friction because when angle of inclination is equal to angle of friction, the component of weight parallel to the plane is just sufficient to overcome the frictional force.

A body on an inclined plane just tends to slide down if the angle of inclination is equal to the angle of friction because when angle of inclination is equal to angle of friction, the component of weight parallel to the plane is just sufficient to overcome the frictional force.

When angle of inclination is equal to the angle of friction, the body just about to move. But don't move. If angle of inclination slightly increases then the body starts to move. So option C is correct.

If asked about that the body is on the verge of motion then it will be equal to but here it is saying that the body is moving so the angle of the plane should be greater than the angle of friction.

When the angle of inclination is equal to the angle of friction, the component of weight parallel to the plane is just sufficient to overcome the frictional force.

So, Option A is correct.

The angle which the resultant (between the normal and external force) makes with the vertical is called the angle of friction.

Normally, the vertical force is coefficient of friction so greater than inclined angle near the answer.