7
votes
Accepted
Are there torques affecting Earth?
Earth Rotation Variations from Hours to Centuries (Dickey) has some analysis of these variations and states that they are mainly due to interactions with the atmosphere and with the earth's core.
...
- 38.4k
4
votes
Is projection of a simple pendulum, doing SHM as well?
A simple pendulum does approximate shm. Suppose that we displace it through angle $\theta$ from its equilibrium position. If $s$ is its displacement along the arc from its equilibrium position, then ...
- 34.9k
4
votes
Static friction when rolling with constant speed
The torque causes a force $\tau = rF$
on the contact point of the wheel
No. The torque isn't creating any forces on the wheel. On a frictionless surface, the wheel would rotate but no linear ...
- 38.4k
3
votes
Has a heavier atmosphere and the relocation of oil around the Earth had a measurable effect on the rotation of the Earth?
The effect is minuscule, because:
Oil and gas and coal do not come from "the center of the Earth", they come from relatively close to the surface. The deepest oil wells in existence are &...
- 47.2k
2
votes
Accepted
Moment of inertia of a rolling cylinder
The formula $I=\frac{1}{2}mr^2$ for the moment of inertia
of a solid cylinder is only valid, if its density is homogeneous.
But it is not valid anymore, if the density varies with radius.
For example:
...
- 36.4k
2
votes
How to mathmematically direction of friction of spool?
With friction, the bottom doesn't slide. It matches the speed of the table, which is $0$. The spool rolls.
Suppose the spool was sitting on ice, so F was the only force. How would the spool accelerate?...
- 36.3k
2
votes
Static friction when rolling with constant speed
1 There are static frictional forces between the tyre and the ground:
static frictional force on tyre due to ground, and
static frictional force on ground due to tyre.
The first of these two static ...
- 93.7k
2
votes
How does the Dzhanibekov Effect change if replaced with a propeller?
A T-handle has three distinct mass moment of inertia values (indicated below in red, green and blue directions)
As you notice, about the z-axis (blue) the MMOI value of $47\;{\rm kg}\,{\rm mm}^2$ is ...
- 37.4k
2
votes
Static friction when rolling with constant speed
Different contact points
So, I am not entirely sure what other answers you have gotten, but I will say that in my own case, when I was trying to learn about friction on wheels, one of the most ...
- 36.9k
1
vote
Multiplying a force vector by rotated unit vector produces strange results
Please define what $*$ is in $v_3 = F * v_1$
You need to take the dot product, and not any quaternion product or other product.
The reason I suspect you did not, is because the result isn't along the ...
- 37.4k
1
vote
What is the moment of inertia of an I-beam?
Happy that you ask! Here's my solution.
Assume the width and length of the rectangular surface of the upper part of the I-beam are $w\ and\ L$ respectively, and the thickness of the whole I-beam is $...
- 46
1
vote
What is the moment of inertia of an I-beam?
Just use the thin rod formula if the pieces that form the I cross section are small relative to the length.
Wikipedia has a nice list of moments of inertia. For a flat plate (the top and bottom of the ...
- 366
1
vote
Accepted
Why is the output torque less than the input force of 20N applied from a wrench having length of 0.8m?
You cannot compare force and torque - they are different attributes measured in different units. Trying to compare $20$ Newtons with $16$ Newton-metres is like trying to compare $20$ seconds with $16$ ...
- 47.5k
1
vote
Is projection of a simple pendulum, doing SHM as well?
If we have a point moving on a circle of radius $R$ with an angular coordinate $\theta(t)~$ ($\theta=0$ coinciding with the $y$ axis), and we project it onto a line perpendicular to the $y$ axis, the ...
1
vote
Is Joule equivalent to Joule/radian?
A radian has no physical dimension, it's a pure number. So, if you do dimensional analysis,
\begin{equation}
\dfrac{[torque]}{[angle]} = \dfrac{[torque]}{1} = [torque] \ .
\end{equation}
Recalling ...
- 7,146
1
vote
Doubts about the parallel-axis theorem
Consider a body orbiting at some distance around a fixed point and spinning about its center of mass (such that both rotations are in the same plane).
The orbital angular momentum will be that of a ...
- 775
1
vote
Accepted
Vanishing of angular momentum with scale
… the whole universe doesn't possess an angular momentum. It can't: If it had one, the centre would be a special point (which isn't allowed) and the velocities of the outer regions would easily become ...
- 15.4k
1
vote
A pure rolling sphere problem
Initially centre of mass was not at rest. Since it was moving with a constant velocity, it will continue to do so.
Since no force acts (friction wasn't there before because pure rolling was already ...
- 11
Only top scored, non community-wiki answers of a minimum length are eligible