Rotation Definition and 1000 Threads

  1. T

    Could a Tidal Lock Cause the Earth to Stop Rotating?

    So my co-workers and I have had a dispute after hearing a podcast on NPR about Earth's rotation. One question was about what would happen if one side of the Earth always faced the sun (tidal locked) and another question was about what would happen if the Earth stopped rotating. From what I've...
  2. Amaterasu21

    Question about rotating reference frames

    Hello, I have a few questions about rotation and relative motion. Suppose we transport the proverbial spinning ice skater used to demonstrate conservation of angular momentum to beginning physics students to a universe with only her and two planets. She is now spinning in deep space...
  3. W

    Clockwise rotation of the reflection coefficient w/ frequency

    It is always considered that the evolution of the input reflection coefficient, ρ, of a LTI causal passive system with frequency, f, always presents a local clockwise rotation when plotted in cartesian axes (Re(ρ), Im(ρ)), e.g. in a Smith chart, as shown in the attached figure. It must...
  4. W

    Rotation of the reflection coeff. at Smith Chart w/ frequency

    It is always considered that the evolution of the input reflection coefficient, ρ, of a LTI causal passive system with frequency, f, always presents a local clockwise rotation when plotted in cartesian axes (Re(ρ), Im(ρ)), e.g. in a Smith chart, as shown in the attached figure. It must...
  5. AdityaDev

    Is the expression still valid for large differences in radius?

    If a ball rolls in a semicircular track starting from one end of track,( the track is kept vertical) and if radius of ball is r and radius of track is R is this expression correct? (When ball reaches lowest point) ##mg(R-r)=\frac{1}{2}I_0\omega^2 + \frac{1} {2}I\omega_1^2+\frac{1}{2}mv^2## where...
  6. H

    Circular motion in planets and satellites

    Homework Statement A spaceship in outerspace has a donut shaped with a 500 m outer radius. The inhabitants stand with their heads towards the center and their feet on an outside rim. Over what time interval with the spaceship have to complete one rotation on its axis to make a bathroom scale...
  7. C

    Perpendicular force with a spiral

    Homework Statement A red Archimedean spiral is fixed to the ground. An external motor turns a grey support clockwise at w, the support can only turn around itself. On the support there is one orange disk that doesn't turn around itself at start. A stem is on the support. That stem: - turns...
  8. J

    Mounting a small ultrasonic sensor to a continuous rotation servo

    I'm an Arduino electronics hobbyist I'm not a professional electrical engineer. How would I mount a small ultrasonic sensor on a continuous rotation servo, without tangling the wires? How would I fix this problem easily and what's the most common way to mount electronics in a rotating object...
  9. E

    What Does a Rotating Mass in Kerr Metric Rotate With Respect To?

    I understand the Kerr metric has an off-diagonal term between the rotation and the time degrees-of-freedom? That a test mass falling straight down toward a large rotating mass from infinity will begin to pick up angular momentum? Is that what’s called “frame dragging”? Did the Gravity Probe B...
  10. M

    Centripetal force and rotation

    I noticed that if you swing a ball around attached to a string with a centripetal force. The ball also rotates. What causes this rotation? Is there always rotation when there's a centripetal force? does an object orbiting the Earth always face the same way as it orbits?
  11. D

    Does Particle Spin Refer to Rotation?

    Does spin for particles actually refer to spin as in rotation? Or does it mean something else. Do all elementary particles rotate? Without a magnetic field can you have rotation or does the rotation create the magnetic field?
  12. P

    Having trouble understanding General moment

    On the website http://www.real-world-physics-problems.com/physics-of-billiards.html they take this equation ∑Mg = IG∝ where ∝ = -agx/r for the rotation of a rigid body where there is no slipping They then change the equation to F⋅(h-r) = IG(-agx/r) why is ∑MG = F⋅(h-r) when ∝= -agx/r?
  13. E

    Rotation formula Complex numbers

    Homework Statement If arg(\frac{z-ω}{z-ω^2}) = 0, \ then\ prove \ that\ Re(z) = -1/2 Homework Equations ω and ω^2 are non-real cube roots of unity. The Attempt at a Solution arg(z-ω) = arg(z-ω^2) So, z-ω = k(z-w^2) Beyond that, I'm not sure how to proceed. Using the rotation formula may also...
  14. CaptainSiscold

    Angular kinematics: determining satellite orbital radius

    So, I'm working on my semester finals for my high school physics class, and I've run across a problem that has me stumped. I've included the pertinent material below. Homework Statement A rocket with a mass of 2kg and traveling at 14,008.34 meters/second loses 10% of its velocity as finishes...
  15. C

    Rotation of two motors and two disk with friction

    Homework Statement I changed the problem, because I understood my error I forgot a force. It's the same problem with one motor. A motor drives two disks on a support. The support is turning clockwise at w1. Disks turn at w at start. The motor M gives a force F and a counterclockwise torque...
  16. M

    Rotation and centrifugal force

    what is the cause of the centrifugal force from the perspective of the rotating observer? Also is rotation relative like linear motion?
  17. Z

    Rotate System: Polar vs Tangential & Normal

    how do we know which system of coordinates to use whether (polar) or (tangential and normal) in case of a rotating system ??
  18. ellipsis

    Earth's rotation having effect on sub-orbital trajectory

    If you throw a ball obscenely high (ignoring air resistance, etc), and the Earth is rotating, the ball will land in a different spot. Relative to an observer on the Earth, the ball has a sub-orbital trajectory across the surface. If we attach thrusters onto that ball, and have it burn at its...
  19. L

    Entropy of translation and rotation of a molecules

    Homework Statement Hi all, There is a question from the course book: Homework Equations S=k_B ln W The Attempt at a Solution My solution: So first of all, for each molecule, there are 2 motions: translational and rotational. For rotational I get: W_1 =\Omega \left ( \theta \right ) For...
  20. S

    Angular acceleration of a yo-yo pulled with constant force

    Homework Statement A yo-yo is pulled with a constant tension T. The string is horizontal and parallel to the table and unwinding from the bottom of the spool, as shown. The yo-yo's outer radius is R and the spool radius is r. The mass of the yo-yo is m and the moment of inertia of the yo-yo...
  21. B

    How Does a Moving Particle Affect the Rotation of a Spherical Top?

    Homework Statement A solid sphere of mass M and radius R rotates freely in space with an angular velocity ω about a fixed diameter. A particle of mass m, initially at one pole, moves with constant velocity v along a great circle of the sphere. Show that, when the particle has reached the other...
  22. L

    Naive Question regarding Galaxy Rotation Curves

    Many apologies in advance if this question is ridiculous or if it has already been answered on another thread. I've searched and searched through the forums and haven't found the answer - please do direct me accordingly if that's possible. If not - please help! Preamble: We know from...
  23. A

    Newton's second law for rotation, when does it apply?

    I'm reading Halliday's chapter or rigid body rotation. In the derivation of Newton's second law for rotation, it is assumed that the object is hinged about some axis ( the connection would be a frictionless pin). The law is derived for such a connection, but is later applied to objects that...
  24. gracy

    How do these particles rotate about an x-axis?

    Can anyone explain how these two particles actually a complete molecule (given in the image)will rotate about x-axis?
  25. G

    Initial Gyroscopic Precession Using Forces

    I think I more or less understand how a gyroscope precesses--at least mathematically and in terms of torque/angular momentum. My question here is: how does the gyroscope start precessing in the first place? The external forces on the center of mass are entirely vertical. Given that Newton's...
  26. D

    Kinetic energy and direction of rotation

    Hi, I would like to study these two cases: Case A 1/ I turn counterclockwise the ring at w2, this need the energy \frac{1}{2}mr^2w_2^2 with m the mass of the ring 2/ I turn the ring with arm clockwise at w1, this need the energy \frac{1}{2}md^2w_1^2 with d the length of the arm 3/ I eject...
  27. D

    Why Do Spherical Balls of Different Sizes Roll at the Same Speed Downhill?

    Homework Statement Suppose two spherical balls roll down a hill without slipping. If both are released from rest, which one will roll the fastest? The answer is that both will roll at the same speed, even if they are of different sizes and weights, but I do not understand why Homework...
  28. T

    The cause of aerospace rotation

    Hi What is the cause of aerospace rotation whit the earth? May the gravity haves any roll?
  29. G

    Difference between a spinning sphere and rolling one

    Consider this: We have a sphere rolling down a slant, released from some height h with null velocity. At the end of the slant its potential energy will have been fully converted to kinetic energy, part translational and part rotational. Now consider this: at the end of the slant the ball enters...
  30. B

    MHB Matrix Rotation Query: Inertia Tensor D (+90y, -90z)

    [FONT=PT Sans]I have an inertia tensor D in the old Cartesian system which i need to rotate through +90 in y and -90 in z to translate to the new system. I am using standard right hand rule notation for this Cartesian rotation. [FONT=PT Sans] [FONT=PT Sans]D=...
  31. M

    Force applied to dumbbell to CM and edge

    Today in class we learned about how if a force F is applied to a dumbbell on its center of mass and then separately applied to the edge where it gets its maximum torque, the dumbbell will have the same CM velocity after. It makes sense when you think about it in terms of momentum. F times T...
  32. H

    Faraday rotation and permittivity tensor

    Dear all, In textbooks about optics in magneto-optic materials, we often come across a Hermitian permittivity tensor with off-diagonal imaginary components. These components are relevant to the Faraday rotation of plane of polarization of light through the material. Now my question is: Is the...
  33. L

    Rotation angular velocity of a turntable

    I've spent at least an hour trying to figure this out, but can't seem to figure out how to solve this. 1. Homework Statement A 170g , 30.0-cm-diameter turntable rotates on frictionless bearings at 66.0rpm . A 25.0g block sits at the center of the turntable. A compressed spring shoots the block...
  34. A

    Why does the sun appear to move eastwards from Earth?

    Hello, I've been reading astronomy books for some time now but after leaving things for a while I seem to forget rotation directions. For example, I know that the Earth spins in the anticlockwise direction. That is easy to see why. They say that motion of the Earth is eastwards. Because of the...
  35. maxhersch

    Work and Rotational Kinetic Energy (Falling Chimney)

    Homework Statement A tall, cylindrical chimney falls over when its base is ruptured. Treat the chimney as a thin rod of length 49.0 m. Answer the following for the instant it makes an angle of 32.0° with the vertical as it falls. (Hint: Use energy considerations, not a torque.) (a) What is the...
  36. Q

    Are *two* external forces always required to cause rotation?

    As the title says, can there be any rotation if only one force is applied to an object at rest. For instance, if I had a rod laying flat on a frictionless surface, and I pushed one end, am I correct to say that Newton's second law says that all of that force goes into acceleration the center of...
  37. PcumP_Ravenclaw

    Derivation of mapping for isometric rotation about i

    Homework Statement 2. Find the formulae as in (3.4.1) for each of the following: (a) the rotation of angle π/2 about the point i ; Homework Equations The equation 3.4.1 is given below. ## f(z) → z*a + b ## where a, b and z are all complex numbersThe Attempt at a Solution I have attached my...
  38. PcumP_Ravenclaw

    Doubt about rotation isometry on the complex plane

    Dear All, In the 2nd paragraph of the attachment can you please explain to me why we are trying to make ## r(z) = z ## and what does "As r is not the identity..." mean?? and how did the line ## L = 0.5*b + ρe^{θ/2} ## come about? Danke...
  39. PcumP_Ravenclaw

    Derivation of rotation isometry on the complex plane

    Dear all, can you please verify if my derivation of the algebraic formula for the rotation isometry is correct. The handwritten file is attached. The derivation from the book (Alan F beardon, Algebra and Geometry) which is succinct but rather unclear is given below. Assume that f (z) = az + b...
  40. B

    Coriolis Force and the Earth's Rotation,

    /* Last year, in first year I had problems with understanding the Coriolis Force. I asked the lecturer about it and he found a simpler way of explaining it. I thought I had understood. However, I've spent many hours this weekend trying to understand it and it keeps eluding me. That explanation...
  41. Aristotle

    Need assistance in Physics question relevant to Torque & Static equlibrium

    Homework Statement Homework Equations Static equilibrium: Net force & net torque = 0 The Attempt at a Solution Am i doing this correctly for part a? [/B]
  42. L

    The moment of inertia of a rod that is rotating off the end of the rod.

    Is there a formula for the moment of inertia? A thin, uniform density rod is rotating about an axis that is off the end of the rod, so it looks a bit like this: ------- | (------- is the rod and | is the axis of rotation, so the rod is rotating out of the plane of your screen) I just have...
  43. S

    What is an example of a proper rotation in physics?

    An example being its use in the beginning of this document: http://isites.harvard.edu/fs/docs/icb.topic1288789.files/Rotations-Lorentz-Transformations.pdf I haven't read the whole document yet so forgive me if it explains what it means later on.
  44. S

    Proof of disk moment of inertia using area density

    Homework Statement Disk with radius R σ = M/A I = ∫ mr2 Homework Equations Today we learned how to derive various moments of inertia via density equations (M/L, M/A, M/V). I understand all of them except on how to get MR2/2 for a disk. The Attempt at a Solution I = ∫mr2 σ = M/A dM =...
  45. V

    Double rotation, friction and sum of energy

    Hi, I posted my question on another forum: http://physics.stackexchange.com/questions/143377/one-disk-ring-in-double-rotation-and-sum-of-energy but it is "on hold" and nobody knows where is the error, so I try to post here if you are agree ? I can understand if you close the question...
  46. Logan Land

    MHB How to solve the following matrix rotation

    Find the standard matrix for the rotation of 60◦ about the axis determined by the vector v = (3, 4, 5). do I multiply each x,y,z by pi/3? doesnt seem like it should be that simple
  47. nicolauslamsiu

    Tides: Does Moon's Rotation Affect Earth?

    Apart from the the gravitational pull of the Moon and the Sun on the Earth, does the rotation of moon contribute to the tides?
  48. P

    B. What is the net force acting on the object?

    Homework Statement A uniform disk 0.3m in diameter and having a mass of 2 kg isfree to rotate about its horizontal axis on frictionless bearings.An object with a mass of 0.05 kg is attached to a string wound around the rim of the disk. The object is released from rest and descends with constant...
  49. P

    Torque vs Centripetal Force: What's the Difference?

    Torque causes a system to rotate about its axis while centripetal force causes a system to rotate about the axis of the separate system that exerted the centripetal force. So does this mean that torque specifically causes rotation and centripetal force causes revolution?
  50. F

    Rotation Problem - Constant Acceleration

    Homework Statement [/B] At t=0, a flywheel has an angular velocity of 3.4 rad/s, an angular acceleration of -0.42 rad/s^2 and a reference line at \theta_0 =0 A: Throigh what maximum angle will the reference line turn in the positive direction B: At what times will the reference line be at...
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