What is Rotating bodies: Definition and 25 Discussions

A rotating frame of reference is a special case of a non-inertial reference frame that is rotating relative to an inertial reference frame. An everyday example of a rotating reference frame is the surface of the Earth. (This article considers only frames rotating about a fixed axis. For more general rotations, see Euler angles.)

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1. What should be the geometries of two contacting solids that may have a relative rotation and translation along the same axis?

TL;DR Summary: What should be the geometries of two contacting solids that may have a relative rotation and translation along the same axis? a) Consider two rigid bodies that have a relative motion characterized by a rotation and a translation with respect to the same axis (like a bolt and a...
2. I Solving Wheel Coming to a Stop: FBD, Friction & Hysteresis

Simple question. Let's say a solid cylinder has an initial speed ##v_o## and it's rotating on infinitely hard ground without air resistance. The cylinder will come to a stop eventually. There are two sources of friction. Since the wheel/cylinder is deformed at the contact patch, there is some...
3. Torque about an accelerating point

The total force acting on the pulley is zero so: F=mg+T1+T2 (1)Analyzing the torque and angular acceleration about the actual axis of rotation, the axle of the pulley, gives: τnet=T1R−T2R=Iα (2)If we analyze about point P, the right edge of the pulley where T1 is applied, we get...
4. I Angular velocity of a rod and what formula to use while solving.

The question is: A uniform rod of length ##L## stands vertically upright on a smooth floor in a position of unstable equilibrium. The rod is then given a small displacement at the top and tips over. What is the rod's angular velocity when it makes an angle of 30 degrees with the floor, assuming...
5. Getting wrong answer in an (angular) impulse momentum problem

I have tried this same approach three times and I got the same answer. I can't figure out what's wrong. Btw answer is 12mu/(3+cos2α) And yes, sorry for my shitty handwriting. If you can't understand the reasoning behind any step then please let me know.

11. What causes an object to rotate?

Hi I've been taught that any force not going through the centre of mass will create torque. Consider a rod of length ##L## and negligible mass, with two balls of mass ##m## attached to its ends. Its centre of mass is at ##\frac{L}{2}##. I have two questions: 1) If a force ##F## is applied to...
12. Rotation around a non fixed axis + linear motion of a system

I have had a thought experiment in my head for a while now and I am unable to find clear enough examples/info that deal with similar issues, to solve it on my own. This is why I hope that someone in this forum can at least point me towards a solution or provide hints as to where should I be...
13. Mathematically Modeling a Rolling Body with Slipping

Basically, I want to know if my assumptions and workings are correct. This is how I see this situation. First, I'm viewing this body as a series of disconnected points, like I have in this animation I made, modeling purely rolling motion. Modeling the body like that worked in that case, and...
14. A rotating system of two point particles with inner torque

Lets say we have a system of two point particles (1. and 2.) which are rotating around an axis. What is written next in my physics course book is: The torque of a 2.body on the 1. body is M21=r1xF21 and the torque of the 1.body on the 2.body is M12=r2xF12. Understandable. But how? There is no...
15. Rotating Bodies Around Origin: Analyzing Motion & Dynamics

Homework Statement Hello! I have 2 bodies initially at rest, of equal masses with the distance between them a and coordinates ##(a cos(\theta),a sin(\theta))## and ##(-a cos(\theta),-a sin(\theta))##. If we denote ##a_x## and ##a_y## the horizontal and vertical distance between them they...
16. Which will reach the bottom faster: solid or hollow sphere?

1. The problem statement: Consider a solid sphere and a hollow sphere, of equal mass M and equal radius R ,at rest on top of an incline . If there is no slipping which will reach the bottom faster. 2. Homework Equations : acm = Fext/M (cm= centre of mass) angular acceleration= torqueext/ I ( I...
17. Deriving Møller's Relativistic Minimum Radius for Rotating Bodies

Can someone either derive or point me to a derivation of Møller's formula for the relativistic minimum radius of a rotating body? I've been searching for about an hour and it's driving me crazy! The only "minimum radius" equation I've seen imposes the speed limit c on a classical rotating body...
18. Newtons 2nd law for rotating bodies

Is shown like this in my book: Consider a rotating body with an angular acceleration α. There must be a tangential force component if it is rotating: For a general point on the body we can write: Ftan = mi * ai = mi * ri * α (1) Multiply by ri and sum up you...
19. What causes angular momentum in rotating bodies

Starting at BB everything moves outwards with linear momentum so unless the BB event was rotating where does the angular momentum come from, the Earth rotates, it orbits the sun, the galaxy is rotating and the sun orbiting within it. So it seems that angular momentum is the norm for bodies...
20. Only rotating bodies have angular momentum

Only rotating bodies have angular momentum? Is this statement false? I had read it somewhere that it is false that only rotating bodies have angular momentum, angular momentum = moment of inertia * angular velocity. Both deal with rotation. so how is the above statement false?
21. How does SR apply to rotating bodies?

Suppose I have a disk that is 100,000 km in diameter. I attempt to rotate it at 1 revolution per second. Am I unsuccessful because the material on the outside edge would have to travel faster then light or am I successful because length contraction at the outside edge reduces the...
22. Rotating bodies, Car around a corner

Homework Statement A car turns a corner with a radius of curvature of 11.1 m while braking to reduce its speed. If the brakes generate an angular deceleration of 0.5 rad/s2 what is the magnitude of the acceleration of the car half way through the corner when the car's linear speed is 9.6 m/s...
23. Acceleration and rotating bodies.

Homework Statement Ok, when talking about rotating bodies, we deal with the following accelerations - please correct me if I am wrong: A radial acceleration (a.k.a. the centripetal-acceleration): w^2*r or v^2/r. An angular acceleration given by dw/dt. A tangential acceleration given...
24. How Do Moment of Inertia and Angular Velocity Compare Two Rotating Bodies?

If there are two rigid bodies rotating, (known I) how can you compare their rotation? Example: If the object of moment of inertia I is spining at x rad/sec, and its I is changed to i, what is the new speed?
25. Understanding Angular Momentum Conservation in Rotating Bodies

im supposed to show why angular momentum is conserved in a rotating body with no external torques or forces acting on it. i know to use the I_1*w_1=I_2*w_2 where I is the moment of inertia of the object in motion and w is the angular speed. My qu estiosn are: which equation for Inertia...