rotating

  1. Like Tony Stark

    Relative rotational motion on a disc

    The first doubt that comes to my mind is "I have to determine the acceleration with respect to what?", because the problem doesn't tell. Then, I have some problems when having to plug the data in the formula of acceleration. ##\vec a_B=0## because the origin isn't accelerated, ##\vec{\dot...
  2. C

    I Rotation or acceleration defined without relation to something else

    Starting from this post, we are able to define the concept of (proper) acceleration or rotation without any reference to something else About this definition which is the physical meaning of gyroscopes axes pointing in three mutually orthogonal spacelike directions ? In other words, from a...
  3. T

    A ball (sphere) rotating along a moving incline

    1. Homework Statement We have a ball of mass ##m##and radius ##r##. it is placed on an incline (We don't know the angle of the incline, nor we do whether the angle is constant along the incline - maybe it is a curved incline) and then released. The COM of ball is ##h## meters above the incline...
  4. marino

    Power generated by a coil rotating in magnetic field

    The problem: a coil of radius r, length l and N turns, rotating with constant angular velocity ω around an axis perpendicular to its simmetric axis and passing for the center of the coil. The coils is submersed in a static magnetic field, intensity B0, perpendicular to the axis of rotation of...
  5. L

    I Quick Question: Rate of Change of a Rotating Vector

    Is the equation presented (that the time-derivative of a given vector in such a scenario is equal to its angular frequency vector cross the vector itself) true in the case of a vector whose origin is not on the axis of rotation? The way I'm visualizing this, if we take such a displaced origin...
  6. J

    Maximum height a waitress can push on a glass without it tipping

    1. Homework Statement I have attached the problem. I will write it out: A waitress attempts to push a glass of water of heigh 15.o cm and diameter of 7.00 cm on a dining table, as shown in the figure. If the coefficient of static friction between the glass and the table's surface is 0.350...
  7. Mind----Blown

    I General approach to find principal axes of rotation?

    Suppose i have an equilateral triangle and i want to find the principal axes of rotation passing through one of the vertex. How can i do that? I am thinking along the following lines but i'm not too sure: 1)Since the equilateral triangle has symmetry about a median, that definitely is one...
  8. hansyhop

    Motorized rotating platform (180 degrees, periodically)

    Hi, I'm trying to build a motorized rotating platform, and was wondering what drive system to choose. The platform is 1.2 meters in diameter with two cylindrical objects (max 25 kg each) attached on top - total weight to rotate approx 80 kg. I want the platform to be programmed to...
  9. V

    I Should I consider Linear Kinetic Energy in this Equation

    Sorry If the thread name confuse you. I want to know if I want to find the Torque from deriving Kinetic Energy and the system has Object the Rotate and the rotating cause linear motion(v). Let's say it a Rolling Disc on the non-slope plane which has angular velocity ω and that ω cause it to move...
  10. hadsox

    Rotating and translating spool across a table

    1. Homework Statement A uniform spool of mass M and diameter d rests on end on a frictionless table. A massless string wrapped around the spool is attached to a weight m which hangs over the edge of the table. If the spool is released from rest when its center of mass is a distance l from the...
  11. cheapstrike

    Rolling of a disc

    1. Homework Statement A cart with mass M has four wheels (idealized as uniform discs), each of radius r and mass m, arranged symmetrically with respect to the cart. Find the acceleration of the cart when a horizontal force F is applied on it. There is no slipping between the wheels and the...
  12. G

    Work-Energy for Bead on Rotating Stick

    1. Homework Statement Verify the Work-Energy Theorem W=ΔK for a bead of masd m constrained to lie on a frictionless stick rotating with angular velocity ω in a plane. 2. Homework Equations W =∫ F⋅dr, K =m/2 v^2 3. The Attempt at a Solution Adopting polar coordinates the velocity is v = r'...
  13. PM22

    Formula to calculate force as a function of angle

    What formula can I use to calculate the force I need to apply to a sliding arm that makes a point contact along the edge of a rotating arm attached to a shaft driving a load in order to push the rotating arm to rotate the shaft? The rotating arm is 1 cm wide. The load at the shaft is 1 Nm...
  14. X

    Rotational Motion of a pendulum

    1. Homework Statement A pendulum is made of a bob dangling from a lightweight string of length ℓ. The bob is pulled sideways so that the string makes an angle θi with respect to the vertical, then released. As it swings down, what is the rotational speed of the bob as a function of the...
  15. B

    Two Rotating Disks Contacting Along Edge

    1. Homework Statement Two disks, rotating in the opposite direction of the other, are held together on their rotating ends, acting as toothless gears. The bottom disk is slightly skewed in one direction, and therefore causes a frictional force on the top disk, and thus an equal and opposite...
  16. Gonzalo Chumillas

    B What does mean that a black hole is spinning?

    The angular momentum is related to the rotation. And when a black hole has angular momentum, it is said that it is a "rotating black hole". But what does it mean? A black hole does not have a conventional surface, like a basketball. How should we interpret that angular momentum? I asked this...
  17. S

    I Rolling without slipping taking the contact point as pivot

    I'm confused about this rolling without (or better with) slipping situation. Suppose to have a disk with initial velocity ##v## and angular velocity ##\omega##. The motion is to the right but the angular velocity is counterclockwise. There are no forces acting on the disk besides the kinetic...
  18. S

    Torque on barbell when angular momentum is not constant

    1. Homework Statement Consider a barbell with two equal masses m that rotates around a vertical axis z not passing through its center with angular velocity \vec{\omega}. The barbell is forced to stay in this position by an appropriate support. Identify the forces exerting torques on the system...
  19. kostoglotov

    System of ODEs in a rotating coord. system

    1. Homework Statement imgur link: http://i.imgur.com/pb14Q4Q.png 2. Homework Equations 3. The Attempt at a Solution The thing I don't understand is where the first two terms of each 2nd order ODE came about. I understand that they are there because the coordinate system is rotating...
  20. B

    Mathematical modeling of the deflection of a rod

    A rod is radially mounted on a motor shaft and provided with a flat end plate. By turning movement, the end plate will touch a pointed object, and the angle turned is measured.By the torque of the motor during acceleration and deceleration, a vibration and deflection happens on the rod. The...
  21. 2

    Why is kinetic energy due to a planet's rotation treated as negative?

    1. Homework Statement I am trying to answer the following question: Among the animals that appear in the zoo of the Universe there are black holes and neutron stars. The mass of each of these is often the order of the mass of the Sun. The radius of a neutron star is about 10 km and a certain...
  22. C

    Kinetic energy of a rotating and translating body?

    1. Homework Statement Not a homework or coursework question, but given the simplicity of the problem I feel that this is an appropriate subforum. Consider a person spinning a rock on a string above their head at a constant angular velocity, walking away from the observer at a constant linear...
  23. T

    Confusion with the centrifugal foce and potential energy

    When we release a suspended object, we recover the potential energy due to gravity as the object travels back through the height raised. When we release an extended spring, we recover the potential energy as the object travels back through the distance stretched. But when we release a rotating...
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