# What is Rotate: Definition and 244 Discussions

A rotation is a circular movement of an object around a center (or point) of rotation. The geometric plane along which the rotation occurs is called the rotation plane, and the imaginary line extending from the center and perpendicular to the rotation plane is called the rotation axis ( AK-seez). A three-dimensional object can always be rotated about an infinite number of rotation axes.
If the rotation axis passes internally through the body's own center of mass, then the body is said to be autorotating or spinning, and the surface intersection of the axis can be called a pole. A rotation around a completely external axis, e.g. the planet Earth around the Sun, is called revolving or orbiting, typically when it is produced by gravity, and the ends of the rotation axis can be called the orbital poles.

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1. ### B Homopolar motor rotation in Vacuum

Hi again, I've found interesting video. Roller homopolar motor : Roller Motor Do you think the motor from 1:08 min Will self rotate in Vacuum/Space (No other forces : Gravitational or Other type.) Thank you in advance.
2. ### Torque needed to rotate a rack

The weight of the rack is supported on an axial bearing as seen in the attached pdf below. I have made an attempt to calculate the torque by taking a look at the chain traction force and the required shaft power to make the plates rotate. For the moment of inertia case i don't know how to treat...
3. ### I Figuring out the torque required to rotate a dome

Hello, Assuming the dome will not spiral away using a single motor and is set up in a manner such that it would rotate in place, I want to find the minimum torque needed to rotate a fairly heavy dome if a motor was located on the dome's inner face. I understand that this is an issue that...
4. ### Torque to rotate a object on the ground about its own axis

Hi, I have an object sitting on the ground, with a coefficient of friction (COF) of 0.3. Lets say it is a square block, and will rotate on its central axis. How much torque is required to rotate this block? I am ignoring inertia weights as will be rotating very slowly.I can solve my problem by...

6. ### The torque required to rotate 675 lbs mass?

Hello everyone, I am trying to design a fixture that can clamp onto and turn an equipment 180 degrees for maintenance. I am trying to figure out what torque will be required at the hand wheel to turn it. The piece of equipment will be clamped at its center of gravity. However, its mass is not...
7. ### I Will this dipole rotate or change position?

Will this dipole rotate or change position? The external electric field is in black. Two charges with their electric fields are drawn in orange.
8. ### Rotate Points on Sphere by Theta and Phi

Dear Forum, My goal is to rotate several points on a sphere by a theta and phi. For example, I have a sphere where the elevation is theta (90 to -90) and the azimuthal is phi (-180 to 180). I have the following points on the sphere: theta = [45 45 45 45] phi = [-180 90 90 180] This generate...
9. ### I How to calculate the HP/torque required to rotate a dual sprocket/chain system?

Hi, I am trying to determine the HP motor/torque that will be required to rotate the sprocket/chain system in the image below from a resting position. The sprockets will be at rest, rotate 5 degrees, come to a stop for 5 minutes, and then rotate again 5 degrees, repeated. The speed of...
10. ### What electric motor do I need to rotate a platter that weighs 6 - 10lbs?

Would a DC motor that had torque of 0.34 Nm be able to generate enough power to rotate a platter that weighs 6 - 10lbs
11. ### B Calculating the torque needed to rotate a drum

Imagine this: You have a drum with a radius of 12cm, around that drum is a toothed belt which is connected to a motor. The drum weighs 10kg The motor should be placed under the drum How would I calculate the amount of torque needed to rotate the drum I don't have any idea how to calculate this...
12. ### Torque required to rotate a plate in a fluid

Hello all:) thanks for the help. This is for my fluids class. This is an example problem and I am stuck on it. ok, so i found a video on youtube which walks through the entire process, but I am confused at a few sections. Here is the link to the video so you can follow: at time stamp 2:37...
13. ### I Trying to rotate a disc about two perpendicular axes

I've a disc which can rotate freely about two perpendicular axis (fixed to the body) If I simultaneous try to rotate it about the two axis, what will happen?
14. ### Around which point does an aircraft rotate during the landing flare?

Without giving possible options, as to not lead people in a wrong direction perhaps, I have a question I am struggling with. Mostly because I get different answers from different people 🤔 When an aircraft is coming into land and starts the landing flare, around which point does it rotate? It...
15. ### B What Would Happen if the Earth Stopped Rotating?

If the Earth did not rotate, would one side always face the sun and the opposite side always be in darkness? Or would a day be six months, and a night be six months? Or something else?
16. ### Angular velocity of a weighted rod left free to rotate around a pivot

Hi guys, I don't really know how to solve this problem. The point is finding ##\omega## when ##m_2## passes from ##m_1##'s original position. Ideally, I'm thinking about some conservation of energy/momentum to apply here, but I'm quite confused. Any hint?
17. ### Does every object rotate around its center of gravity?

It is said that rocket,plane rotate about center of gravity ,why this is is not case for boats? Boat pivot point is not in center of gravity.
18. ### Optical Compact Device For Measuring Speed of Light

Hi. This is an idea which I just happened to think of, and I was curious if it would be at all feasible. Here's a quick sketch I drew: The two curved mirrors should have a laser attached on one end and a video camera attached on the other. The laser would be tilted very slightly above...
19. ### Python Rotate 2D Gaussian given parameters a, b and c

I have a Gaussian function of the form: def f(x,y): a=some number b=... c=... return 3*np.exp(-a*(-0.5 + x)**2+b*(x-0.5)*(y-0.5)-c*(-0.5 + y)**2)This is a Gaussian function symmetric around y=x, and I'd like to rotate it 45 degrees (counter)clockwise. Wikipedia gives an overdetermined...
20. ### Calculation of time taken for a motor to rotate an object 360 degrees

How would I go about calculating the time taken for the motor on page 2 to move the attached beam 360 degrees? Things such as the rpm and voltage are given in the attached data sheet for various different motors and you can reference anyone you like. I'm more interested in understanding what's...
21. ### 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...
22. ### Some airplane pilot jargon: "Rotate", "Heavy"

Having watched slew of documentaries about (civilian) air crashes, I wonder about some oft-heard jargon. A airline flight is often referred to with the adjective "heavy". For example, "AA 191 Heavy". What does "heavy" indicate? During takeoff, the monitoring pilot says "V-1" to indicate...
23. ### Minimum force required to rotate a lamina

When the lamina rotates about A, FA must act on B (because it is the farthest away) perpendicular to AB (so that all of FA contributes to rotation). Same argument is valid for rotation of lamina about B as well. Having noted that, I tried two approaches: Approach 1- If I assume that the...
24. ### Why do objects always rotate about their centre of mass?

Why do unconstrained objects always rotate about the lines passing through their CMs when tangential forces are applied to them? I understand that if an object does not rotate about its CM, then its rotation will decay to the rotation about the axis passing through its CM. Also, when a roller...
25. ### An isolated object can rotate only about its center of mass

I was talking to someone about the equilibrium of fluids and we reached at some stage where we had to prove that in an external field the translational forces add to zero along with moments (torques) should also add to zero. The first one was quite easy but during the discussion of second...
26. ### What causes unhinged objects to rotate?

Suppose their is a unhinged rod lying on table and someone applied force at some point then due to it object start rotating.i tried to find why it rotates and came to know that if line of force is not passing through the centre of mass then force will produce torque around the centre of mass...
27. ### Rotate IMU data to obtain correct measurement data

Hi I have collected data from a IMU on a boat. Currently I am using the angular velocity measurement vector ##\omega^b_{imu} = \begin{pmatrix} p\\q\\r\end{pmatrix} ## for use in kalman filter, where superscript ##b## is BODY frame. The BODY frame is given be x-axis pointing forward, y-axis...
28. ### Press and release a button to rotate an object?

I'm going to hire a ME to do this but I first want to know whether it is at all doable, exactly what is needed here and what design specifically has to be requested. Here's a sketch of the desired device: Proportionally and size-wise it shoud be similar to a pen. Rotation should be around 10...
29. ### A uniform rod allowed to rotate about an axis and then it breaks

A uniform rod AB of length ℓ is free to rotate about a horizontal axis passing through A. The rod is released from rest from the horizontal position. If the rod gets broken at midpoint C when it becomes vertical, then just after breaking of the rod. Choose multiple answeres from the below...
30. ### I Rotate a shape back to its original position with the fewest rotations

Summary: Rotate a shape back to it's original position with the least amount of rotations. Lets say you have a cube. It's starting rotation is (0,0,0). It can be rotated on each axis ( x,y,z ) no more than once each by 90 or -90 degrees (rotation can also be skipped for any axis). The shape...
31. ### How can I rotate Euler angles through a specific angle?

Summary: I found an old topic on this forum that describes a similar problem to what I am facing currently. I want to rotate an object with euler angle values, but the rotation has to be translated based around a specific angle. However, I do not fully understand the solution provided in that...
32. ### Torque required to rotate an object at an angle

I am trying to work out the torque required to rotate a platform, initially declined at an angle. See attached hand sketch. My situation is - I have a platform initially at a declined angle, say at 0 degrees. - I have a load at the end of the platform at 0 degrees - I want to be able to...
33. ### Does Earth's Rotation Affect Our Perception of Weight?

In the early 17 th century people argued that the Earth can't be rotating because the don't feel any movement. How fast would the Earth have to rotate for us to feel the effect of rotation and have no doubt of its rotation?
34. ### A question about magnetism that causes a wheel-loop to rotate

This question is from 1977 AP Physics C so I suppose it would be clear enough, but I am confused about question c. Question a is easy (it rotates counterclockwise), question b too (Στ=6*rxF=6*r x (I*i x B)=0.06). Question C is where I am stuck. The diagram provided with the question looks like...
35. ### Torque required to tilt 1200 kg mass?

Object to be tilted = 1200mm diameter cylinder Cylinder height = 2.5 meter weight of tilting assembly = 1200 kg Cylinder is on platform which is "L" shaped and tilting point is on that corner of "L" as in attached image. Shaft diameter on which it is tilted id 63mm Angular acceleration = 0.05236...
36. ### Will the 2 dimensional sphere rotate?

Homework Statement A 200kg sphere is in touch with two walls. The horizontal wall has no coefficent of friction and the vertical has μ=0.25. If we apply a force F=400N will the sphere rotate? Homework EquationsThe Attempt at a Solution [/B] What I can't understand is, if there is balance in...
37. ### Torque required to rotate a hollow cylinder containing chips

I am designing a prototype to remove cutting oil from waste metal chip during Gun Drilling. My prototype consists of a netted(meshed) metal cylinder rotating horizontally about its axis with help of shaft and a pressurised air blown from above. The metal chips will be put inside netted cylinder...
38. ### B Why most stars seem to rotate the same direction in a galaxy?

After much questioning and soul-searching I got my answers of why galaxies rotate, and for that I greatly thank the gurus in the forum (so I'll not forget: conservation of initial angular momentum, non-isotropic material scattering, slowdown of infalling materials and non-isotropic infalling of...
39. ### Automotive Can two motors rotate about the same axis?

can we add two motors to rotate same object on same axis or is it impossible? for a stronger rotation and torque two motors rotating object in same direction
40. ### Why do hurricanes rotate counter-clockwise?

In the northern hemisphere, they rotate counter-clockwise. In the southern hemisphere, they rotate clockwise. This is often attributed to the Coriolis effect, an apparent deflection of moving objects in a rotating frame of reference. While this is true for deflected artillery shells, it is NOT...
41. ### B Why do most of the celestial bodies rotate about their axis?

Every celestial body revolves around a relatively massive celestial body due to the gravitational influence. But what is the reason behind their rotation about their own axis? What thing initially triggered their rotation? Does it have something related to the origin of the universe?
42. ### Power required to rotate a load of specific weight

Homework Statement Weight - 200kg RPM - 5 Diameter - 6m Homework Equations Moment of Inertia I = (weight/9.8).r^2 Torque t = I * (angular velocity / t) Power = Torque * speed The Attempt at a Solution First I calculate Moment of Inertia Using I=(weight/9.8) * r^2 = 183 kg. m^2 Then I...
43. ### How long to rotate *One* degree?

Hi, Feels like a simple one but for reason I am stumped. If I am rotating at 11.2 rad/s, how long will it take to rotate ONE single degree? - Converting 11.2 rad/s into °/s, I get 641.71 °/s. So, this is equivalent to 1.783 rev/s. At this point, do I divide 1 revolution by how many degrees I...
44. ### Two masses connected by spring rotate around one axis

Homework Statement Take the x-axis to be pointing perpendicularly upwards. Mass ##m_1## slides freely along the x-axis. Mass ##m_2## slides freely along the y-axis. The masses are connected by a spring, with spring constant ##k## and relaxed length ##l_0##. The whole system rotates with...
45. ### Why does it get harder with time to rotate a screw?

A couple of forces act on the screw and create the turning effect. But after sometime it gets harder. So, net torque is decreasing, but why is it decreasing? Frictional force comes into action, but friction doesn't depend on surface area. So, frictional force will remain constant. So what...
46. ### Calculating the torque required to rotate a ski on snow

Hello friends, I'm currently working on an engineering competition project known as the Great Northern Concrete Toboggan Race, and I'm stuck on some preliminary calculations. I'm trying to calculate the amount of torque that will be required to rotate the front skis in order to turn the...
47. ### Will a sphere rotate on a frictionless inclined surface?

Well, my physics teacher taught us about rotation the other day and I came across a scenario where a sphere and a ring roll down a friction-less inclined plane from a point of absolute rest. I found it counter-intuitive as I started to think about why would they start rolling in the first place...
48. ### Pendulum on the end of a rotating disk

Homework Statement There's a pendulum with mass m and longitude L strapped to a disk with radius R that rotates with an angular velocity ω. Calculate the angle that the pendulum is shifted (Φ) depending on ω. You are given m, L, R, ω, g. Calculate Φ depending on ω. Little drawing (with my...
49. C

### How will the magnetic field change if I rotate the solenoid?

If I do the x-axis rotation for a solenoid, how will the magnetic field change? Would it also rotate along x axis?
50. A

### What composition of steel pipe should I use

Hello, I work in a apparel manufacturing warehouse and I'm planning to upgrade the Jacket Hanger Racks to a rotatable conveyor. So I want to insert new Steel Pipes for hanging the Jackets which will rotate. So, the length of the pipe is 370 cms / 12' 2", and the weight it will be holding is...