Recent content by mrsobhan

you must also account for normal force that exerts from the ground on the ball

you said" "When the funnel starts rotating, do you mean that the block remains at rest at the bottom?" my answer: yes I think so. If there is not any friction then the block will remain at the bottom of the funnel.

OK but "some force towards the center" is not a force that comes magically when the mass rotates. This force is simply the sum of two forces; gravity and normal force. you may ask the normal and gravity forces exist when the block does not rotate. Yes but the magnitude of N is different when...

yes you are right. But pay attention that from an inertial observer's point of view (for example someone stands on the ground) there are only two forces: N and mg. Ok you may say "so, how the block can remain at its place without sliding" and the answer is: "For someone outside the funnel i.e...

evidently this is m*g*sin(theta) and its direction is parallel to the inclined surface of the funnel. Any way we have only two forces mg and N.

yes the N vector can be shown by the sum of two components: Nsin(theta)*i + Ncos(theta)*j which i and j are unit vectors of cartesian coordination. we can also write mg like: -mg*j also the vector representation of acceleration is: -a*i Then we write the sum of forces: F = ma (F and a...

thanks. but don't forget that centripetal force is not a real force. That is, when you draw free diagram of forces you don't include such a force. In free diagram you just enter Normal force, Gravity and friction (if exists). Then you set the sum of these vectors to m*a which a is the...

Homework Statement We have an inclined cylinder, something like a funnel, which rotates around its symmetrical axis. A mass (m) resides on the wall of this cylinder and rotates with the cylinder. Now the angular velocity of the cylinder increases. Whether the Newton laws (or else) can...

Thanks. We reached the good point now. Consider a rotating disc with a mass on it without motion with respect to the disc. As you mentioned above this a case of static friction with the limitation equals to μN. Now the angular velocity of the disc (W) begins to increase. The maximum angular...

ok i accept. But you did not answer the question. What is the direction of the friction with respect to the motion. Suppose that the motion is shown with a vector. For example vector X for displacement. Can you show the direction of the friction force?

Homework Statement We always encounter this expression: "Friction always opposes the motion". But what does it mean exactly? For example when we push a heavy box and it does not move we consider the friction opposite to the applied force. The second case when the box moves. In this case if we...