Tagged Questions
0
votes
0answers
17 views
What determines the motion in a Newton's craddle? [duplicate]
Let's say we have a Newton's cradle with five metal balls, each with a mass $m$. You pick up one and release it, and right before impact it has a velocity $v$. What determines weather the ball at the ...
2
votes
1answer
49 views
Energy in a wind instrument?
My physics teacher said that he saw a guy playing a very large wind instrument on TV, and the guy apparently calculated that the total energy present in the instrument when he was playing was almost ...
2
votes
1answer
43 views
Finding the coffecient of restitution
A ball moving with velocity $1 \hat i \ ms^{-1}$ and collides with a friction less wall, afetr collision the velocity of ball becomes $1/2 \hat j \ ms^{-1}$. Find the coefficient of restitution ...
-1
votes
1answer
117 views
Confusions about rotational dynamics and centripetal force
I am a high school student. I am having confusions about the centripetal force and rotational motion . I have known that a body will be in rest or in uniform velocity if any force is not applied. But ...
4
votes
0answers
60 views
Scaling arguments for the Contact mechanics between two elastic spheres
I am studying a bit granular dynamics and I have seen that two spheres of radius $R$ in contact with a contact area of radius $a$ would need an applied force $F$ on this two spheres that is nonlinear ...
0
votes
1answer
58 views
Hollow stone columns provide more support?
In history class in elementary school I remember learning that the Greeks would build their stone columns hollow because they thought this provided more support. Is it true that a hollow column is ...
4
votes
2answers
181 views
Why is the Lagrangian quadratic in $\dot{q}$? [duplicate]
My teacher said we only consider Lagrangians which are quadratic in $\dot{q}$, and we don't take other Lagrangians. I couldn't understand why. Can anyone please explain this?
1
vote
0answers
69 views
Limitations on the choice of axis of rotation regarding rolling wheels
Consider a situation where a wheel is rolling without friction on a level surface. Call the center of the wheel $C$, the point where the wheel contacts the ground $G$, and some arbitrary other point ...
1
vote
2answers
82 views
How can I understand work conceptually?
I'm in a mechanical physics class, and I'm having a hard time understanding what the quantity of work represents. How can I understand it conceptually?
0
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0answers
45 views
how do the '3d printed magic arms' work? [closed]
this video has been circulating on the internet in the past couple of months, showing how engineers at the Nemours/Alfred I. duPont Hospital for Children used a 3D printer and the power of elastic ...
4
votes
3answers
420 views
An example of non-Hamiltonian systems
I am preparing for the exam. And I need to know the answer to one question which I can't understand.
"Give an example of non-Hamiltonian systems: in case of infinite number of particles; for a finite ...
1
vote
2answers
183 views
Numerical torque calculation
Suppose I can compute interaction energy of two rigid bodies as a function of their coordinates of centers of masses and Euler rotation angles (total 6 + 6 degrees of freedom). Now I can numerically ...
2
votes
2answers
214 views
What sustains a rigid body's rotation at its constant angular(rotational) speed?
Continuing from the following scenario from my previous question Centripetal force of a rotating rigid body? :
Consider someone pushing a roundabout in a playground. Initially the
roundabout is ...
2
votes
2answers
320 views
What happens when the string slackens during vertical circular motion?
Consider a particle attached to one end of a string of length $l$ moving anti-clockwise in a vertical circle whose centre is $O$. What exactly happens physically when the string becomes slack and ...
0
votes
0answers
120 views
Best book for learning sensor fusion, specifically regarding IMU and GPS integration [closed]
I have a requirement of building an Inertial Measurement Unit (IMU) from the following sensors:
Accelerometer
Gyroscope
Magnetometer
I must integrate this data to derive the attitude of the sensor ...
4
votes
4answers
749 views
How do levers amplify forces?
This is really bothering me for a long time,
because the math is easy to do, but it's still unintuitive for me.
I understand the "law of the lever" and I can do the math and
use the torques, or ...
2
votes
1answer
167 views
Static plane in an inertial frame of reference
Suppose we are given a mechanical frame consisting of two points. How can we prove that assuming any initial conditions there is an inertial frame of reference in which these points will be in a ...
2
votes
1answer
174 views
Is there symmetry in 2d stress tensor in linear elastic fracture mechanics?
Assumptions:
Cross terms in strain tensor are defined as equal $\varepsilon_{xy} = \varepsilon_{yx}$.
pure mode I crack.
Far from crack tip, material is purely elastic and we are way below
yield ...
2
votes
0answers
155 views
Why do control moment gyroscopes exhibit “torque amplification”?
There are a number of articles that describe the benefits of using control moment gyroscopes (CMGs) over reaction wheels in inertial navigation applications. One of the primary benefits of using a CMG ...
1
vote
1answer
390 views
Conjugate Variables and Fourier Transforms in Classical Physics
Let q be a generalized coordinate with a conjugate momentum p and a potential resulting in a periodic motion of q. What is the meaning of the Fourier transform of q(t) over its period? Can this be ...
0
votes
0answers
36 views
Trace the path for the following case [closed]
2 identical balls 1m apart are moving in such a way that they are rotation around each other with same speed.
Trace the path followed by them.
1
vote
2answers
269 views
Spin angular momentum of a system of particles : Is there any energy associated with it?
Consider a system of point particles , where the mass of particle $i$ is $μ_i$ and its position vector is $\vec{r}_i$. Let $\vec{r}_\text{cm}$ is the position vector of the center of mass of the ...
1
vote
2answers
506 views
What are the expressions for rotational and translational kinetic energies of a system of point particles?
Consider a system of point particles , where the mass of particle $i$ is $\mu_i$ and its position vector is $r_i$. What are the expressions for translational kinetic energy and rotational kinetic ...
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votes
3answers
3k views
Yield Strength versus Ultimate Strength
What is the qualitative difference between these two:
As seen on the table Typical yield and ultimate strengths.
I am trying to resolve the meaning of the phrase "contact yield stress" from C. ...
2
votes
2answers
153 views
Movement of a nudged block on a high friction surface
If I apply a single force to an object ‘floating in free space’, then it will either translate (if the force is in line with the Cof G ) or more generally it‘ll rotate about the C of G due to the ...
2
votes
1answer
211 views
What variables does the action $S$ depend on?
Action is defined as,
$$S ~=~ \int L(q, q', t) dt,$$
but my question is what variables does $S$ depend on?
Is $S = S(q, t)$ or $S = S(q, q', t)$ where $q' := \frac{dq}{dt}$?
In ...
0
votes
0answers
293 views
Calculating torque of actuators? [closed]
How do you calculate the torque of a brushless dc electric motor?
How do you calculate the torque of a hydraulic motor?
How do you calculate the push and pull force of a double acting hydraulic ...
2
votes
2answers
476 views
Does the phase space (configuration and momentum space) of particles have a Euclidean norm? Does it have a useful meaning of “distance”?
Often in engineering physics, different vector spaces are used to visualize the trajectories (evolution) of systems. An example being the 6n dimensional phase space of n particles. It is not very ...
2
votes
2answers
542 views
Stress vs Strain for mild steel
After Yield point on stress strain diagram the under curve occurs what does it mean what will happen for the mild steel at that particular time and again why the curve goes to up and reaches ...
1
vote
2answers
426 views
Spinning bucket of water in zero gravity
Everyone knows how the surface of a spinning bucket of water would look like on earth - parabolic. But what if we turned off gravity (for instance by doing the experiment in a freely falling lift)? ...
2
votes
2answers
269 views
a question on Lagrange's equation when the time derivative of the generalized co-ordinates is constant
Consider a system whose generalized co-ordinates are $q_i$ and is under the constraints $\dot{q_i} = K_i \forall i = 1,2,3,...$ where $K_i$ are constants. I have a problem in writing the Lagrange's ...
5
votes
1answer
110 views
Sum of angular momentum of all electrons in a magnet
Can the sum of angular momentum of all rotating electrons in all the aligned atoms in a permanent magnet have a significant contribution to the macro angular momentum of the magnet? If yes, why does ...
2
votes
1answer
217 views
significance of maxima and minima of time varying kinetic energy of a system
Consider a system of particles where the kinetic energy of the system is varying with time. I'd like to know the significance (or meaning) of the time derivative of the kinetic energy being zero at a ...
6
votes
8answers
4k views
Which Mechanics book is the best for beginner in math major?
I'm a bachelor student majoring in math, and pretty interested in physics. I would like a book to study for classical mechanics, that will prepare me to work through Goldstein's Classical Mechanics. ...
5
votes
1answer
155 views
Why can you assume that the angular momentum vector of a top will always track its axis of rotation?
My favorite physics 101 textbook (Giancoli) explains precession in terms of a spinning top whose axis is tilted from the vertical.
The way the book sets things up, $L$ (angular momentum) points along ...
2
votes
7answers
2k views
What are the Constraints on Building a Tower to Space?
When I was a boy I used to daydream about building a tower so tall that the top of it would stick out of the top of Earth's atmosphere project into near space.
There would perhaps be a zero gravity ...
1
vote
3answers
521 views
Most elegant/fundamental formulations of the laws of classical mechanics?
Newton tried to do it with three laws/statements. While the first can be derived from the second, the three form a pretty nice framework.
Later on, I've encountered Lagrangian Mechanics, which ...
8
votes
2answers
364 views
Shaking a jar of balls
A jar is filled with two types of balls, red and green. Red balls have radius $r_1$ and mass $m_1$, green balls have radius $r_2$ and mass $m_2$.
If initially the balls are randomly placed throughout ...
0
votes
2answers
318 views
Terminal velocity for falling in a shaft
One falls slower in a mine shaft than in free air. This is due to collisions with the walls. How should one model the terminal velocity in the presence of such collisions?
7
votes
3answers
1k views
How long it will take for a upright rigid body to fall on a ground
Let's suppose there is a straight rigid bar with height $h$ and center of mass at the middle of height $h/2$. Now if the bar is vertically upright from ground, how long will it take to fall on the ...
5
votes
3answers
902 views
Equivalent spring-constant for infinite square grid of springs
Consider an infinite square grid, where each side of a square is a spring following Hooke's law, with spring constant $k$.
What is the relation between the force and displacement between two points? ...
4
votes
3answers
671 views
Why does the cart move? [duplicate]
A while ago someone proposed the following thought experiment to me:
A horse attached to a cart is resting on a horizontal road. If the horse attempts to move by pulling the cart, according to the ...
3
votes
4answers
383 views
Rolling stone on a frictional surface
Consider a spherical rigid stone rotating with angular velocity $\omega$ being dropped vertically onto a horizontal rigid surface with the coefficient of friction $\mu$. Can the stone roll on the ...
3
votes
1answer
307 views
Soliton mechanics
How much of classical mechanics can be modelled with solitons?
What I am aware of is that single solitons behave in a way like free particles: they move along as stable entities with constant ...
5
votes
4answers
6k views
Is pushing actually easier than pulling?
It is generally assumed that pushing a cart is more easier than pulling one. But why?
Is there any difference in terms of force required to achieve the same amount of displacement?
Or is it just a ...
7
votes
1answer
508 views
Coriolis force and Newton's third law
I would like to ask a stupid question here.
If a body 'b' moving downward with a velocity v in a rotating frame of reference with angular velocity w, and w and v not being parallel and anti parallel. ...
3
votes
2answers
571 views
Question about moment of inertia and velocity
First off, I swear this is not homework. I'm doing some practice problems because I got an exam coming up. I'm stuck on this one:
I figured I would use energy conservation for this problem. So since ...
5
votes
1answer
470 views
Equilibrium and movement of a cylinder with asymmetric mass centre on an inclined plane
A cylinder whose cross section is represented below is placed on an inclined plane. I would like to determine the maximum slope of the inclined plane so that the cylinder does not roll. The mass ...
11
votes
4answers
1k views
How can I measure the mass of the earth at home?
How can I measure the mass of the earth at home?
How was the mass of the earth first measured?
1
vote
2answers
269 views
Angular Momentum and Force
I'm stuck on number 5. The answers to the first 4 are correct, but I dont know how to set up number 5. Any idea that I would have would require me having some kind of time information, but thats not ...
