# Tag Info

## Hot answers tagged experimental-physics

8 votes

### How damping constant of pendulum varies with length of wire? (experiment result confusion)

It was a good idea, but a pendulum in water will behave differently than a pendulum in air. Looking in section $2$ of your link, Reynolds number is given by $$Re = \frac{\rho L |v|}{\mu}$$ The ...
• 29.9k
5 votes
Accepted

### How damping constant of pendulum varies with length of wire? (experiment result confusion)

The increase in velocity for the longer pendulum does, while increasing the total dampening force, not increase the damping constant. This can easily be shown by analyizing the mechanical problem. ...
• 10.3k
4 votes
Accepted

### Hafele–Keating Experiment. What are the forces acting on the moving clock?

Time dilation isn't a force, and moving clocks always tick at 1 tick per second. However, the "moving" clock and "stationary" clock take different paths through spacetime. This is ...
• 6,651
3 votes

### How can we detect gravity phase-shift in quantum mechanics?

We can detect this using interferometry. It is true that a global phase change on a state, e.g., $\psi\rightarrow e^{i\phi}\psi$ ($\phi$ is a constant) will not change the value of quantities ...
• 27k
3 votes
Accepted

### Would a Magnet Weigh More on a Metal Scale than a Plastic One

It depends. If it's a scale like this: Then it would depend on the mass distribution of the scale, assuming it was all magnetic and same material. If it's a scale like this: then assuming that only ...
3 votes

### How can rigid body have more than 1 speed?

It's not true that "every point on the rigid obj must have same velocity or speed." As you pointed out, if the body is rotating, this is not the case. If the body does have the same ...
• 5,394
2 votes

### Prevent Foucault's Pendulum from an Ellipticity

The classic method is to add a ring somewhere near the top, through which you pass the wire or string that suspends your dumbbell. Make sure the amplitude is so large that with every swing, the wire ...
• 5,454
2 votes
Accepted

### What is a practical experiment in which the position of a quantum particle is measured?

The double slit experiment is typically described as passing a photon or electron through a double slit and letting it hit a screen. A cathode ray tube is an example of this type of screen. The inside ...
• 29.9k
1 vote
Accepted

### What is the smallest entropy value ever measured?

Olf et. al. Nature Physics 2015 (arxiv version) generate a very low entropy Bose-Einstein condensate (BEC) of Rb atoms. They claim an entropy of $S/N = 0.001\text{ } k_B$ where $S$ is the total ...
• 11.7k
1 vote

### What is a practical experiment in which the position of a quantum particle is measured?

The simplest setups that come to my mind: Any photomultiplier tube (PMT) in a dark box with a dim light diode (LED). When you see a signal of the right size, you know a photon has hit its ...
• 5,454
1 vote

### Hafele–Keating Experiment. What are the forces acting on the moving clock?

This is quite simple if you think in terms of a spacetime diagram. As an over-simplified version of the experiment, suppose there is an experimenter on an aircraft whose path is designed to follow ...
• 41
1 vote

### Prevent Foucault's Pendulum from an Ellipticity

About the cause of the plane of swing opening up. (I'm not sure what you mean by 'rotation of the dumbbell itself', I will return to that at the end of this answer.) The upper attachment point of the ...
• 17.4k
1 vote

### How can rigid body have more than 1 speed?

A rotating rigid body has a different velocity (speed + direction) at each point on the body. Only along the rotation axis, the velocity is the same. This is often described as a velocity field, with ...
• 35.4k
1 vote

### How can rigid body have more than 1 speed?

You are confusing linear velocity with angular velocity. Consider a circular rigid body rolling in a plane without slipping. The points in a rotating rigid body do not all have the same linear ...
• 8,552
1 vote

### Which proportions of deuterium and tritium did the National Ignition Facility's hohlraum contain?

Was it a roughly even mix of both isotopes? Yes, as close to 50-50 as they can get. I'm also curious what pressure the "peppercorn" of hydrogen fuel was kept at before the lasers were ...
• 7,661
1 vote

### What is the physical explanation of why a stationary fermion is experiencing zero force from an external static magnetic field?

I think the confusion here is that you intuitively know that a small rare-earth magnet, released between the poles of a large horseshoe magnet, will be pulled linearly (and will snap into contact with ...
• 813

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