# What is Rotational: Definition and 1000 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. ### Compare rotational inertia of 2 paper cups in 2 diff orientations

Figure 1: I assume this is a conceptual question regarding the usage of the above inertia equations but the axes are really confusing me. I would imagine that around I1 and I3, you could say that the total inertia is just the sum of all the ring-shaped "slices" of the paper cups (i.e. use the...
2. ### Avg Power in a Rotational Energy/Work Problem

This question has multiple parts and according to all the work done up to this point... How much work W does the motor do on the platform during this process? 1885 J What is the rotational kinetic energy of the platform Krot,f at the end of the process described above? 1885 J What is the...
3. ### Minimal rotational kinetic energy for a gyroscope to precess

TL;DR Summary: I cannot find any information on how to calculate min. KErot at which the gyroscope does not fall over I am doing a project for school in which I investigate energy loss in a gyroscope. I apply a torque on a gyroscope to initiate its rotation and then measure the time it takes...
4. ### B Rotational Kinematics -- questions about a=mg sin(theta) / (m+I/R^2)

Hi, I am learning. Rotational Kinematics and I was given this formula in class: a=mgsin(theta)/(m+I/R^2); however, I couldn't understand the professor's explanation of where it comes from. Could someone provide some insights about it? I appreciate any help you can provide.
5. ### I Spectroscopy: vibronic and rotational transitions

In spectroscopy, the highest peaks in the absorption spectrum are those that are associated with the most probable energy transitions in a molecule. The most probable transitions are those in which the best superposition between the wave function of the vibronic level of the fundamental state...
6. ### Engineering Measuring rotational speed for Tachometer vs Oscilloscope

Question: Why does the oscilloscope double almost the exact value of rotational speed measured by Tachometer? Rotational speed from Tachometer = 1930 [RPM] Frequency of 1 period = 64.3 [Hz] which means 3857.91 [RPM] The output waveform of hall-effect sensor is attached. Can you have any...
7. ### Rotational inertia of square about axis perpendicular to its plane

For this problem, How do we calculate the moment of inertia of (2) and (3)? For (3) I have tried, ##I_z = \int r^2 \, dm ## ## ds = r ## ##d\theta ## ##\lambda = \frac {dm}{ds}## ##\lambda ## ##ds = dm ## ## \lambda r ## ##d\theta = dm ## ##I_z = \lambda \int r^3 d\theta ## ##I_z = \lambda...

47. ### Controlling the rotational speed of a generator

Hi, I am working on a project that would insert a generator/expander system to a pressurized stream of gas in order to generate electricity. I would like to control the rotational speed of the generator in order to adjust the gas stream flow rate. Would it be possible to control the...
48. ### Rotational dynamics and the conservation of energy

I = Icm + mr^2 I = 0.5 mr^2 + mr^2 I= 3/2 mr^2 By COE, mgh = 0.5(3/2 mr^2)(w^2) g(2r) = 3/4(r^2)(w^2) 8g/3 = rw^2 = v^2 / r v = sqrt( 8gr/3) v=0.511m/s ans: v=0.79m/s
49. ### Rotational dynamics: Resolving forces

Resolving the weight of the cylinder c, i get Mgcosθ (-y) and Mgsinθ (-x) mgsinθ - Fs - T = ma ---(1) (where Fs is frictional force and T is tension) τ = I α (where τ is torque and α is angular acceleration) torque is produced by both tension and frictional force (T-Fs) * r = 0.5 m r^2 α...
50. ### Help with this Ferris wheel rotational physics problem please

So this is what I've attempted: 666 = m*a1 510 = m*a2 a1= ac + 9.8 a2= ac-9.8 666 = m(ac+9.8) 510 = m(ac-9.8) 666 = m*ac + m*9.8 510 = m*ac - m*9.8 156 = 2m(9.8) m = 7.9 kg (which seems very wrong haha) any ideas?? I thought my reasoning was okay, since I considered that at the top of...