# Tag Info

1

The apparent weight is indeed larger when the hourglass is running than at rest. See here for a detailed write-up. This effect has even been verified experimentally. In a nutshell: the net effect of the flow is to move sand from the top surface (where it has a downwards velocity $v$) to the bottom pile, at rest. Thus, the sand is decelerating and the force ...

1

There are quite a few things to consider here. First, The "hourglass" if this vessel is filled with air the results will be much more complex to determine. Second, the diameter of the grains and their uniformity will influence the measurements. Third, The size of the opening will also impact grainflow. Fourth, The sensitivity of the scale in relation to ...

8

Analyzing the acceleration of the center of mass of the system might be the easiest way to go since we could avoid worrying about internal interactions. Let's use Newton's second law: $\sum F=N-Mg=Ma_\text{cm}$, where $M$ is the total mass of the hourglass enclosure and sand, $N$ is what you read on the scale (normal force), and $a_\text{cm}$ is the center ...

4

Imagine an hourglass with just one stone inside. When the stone start to falling a scale would stop to measure it's weight, but it will measure a spike corresponding to the moment when it hits the bottom. The bigger the airtime, the bigger the spike. It is like concentrating the weight of the stone in a very specific time interval: when it hits. However the ...

1

Suppose you are standing on a tower which is on a scale. Jump off. While you're in the air, what does the scale read? (Assume here that you will land on the scale, so the analogy to sand grains holds.)

1

In one sentence: More mass means stronger attraction and less buoyancy (they fall faster), but the effect is negligible in most cases.

6

Suppose you pick two people at random. From one, you pluck a single hair from their head. Is it possible to tell who had the hair plucked by weighing the people? Technically, plucking a hair makes a person very slightly lighter, so you get a tiny bit of information about who had the hair plucked by weighing the people. But the information is very slight ...

1

You might be looking for the tautochrone curve (found by Huygens). The corresponding surface is not an "inclined plane", which might explain the difficulty in googling it.

2

why we always choose the center of gravity of the bicycle be the rotational center. We do not do that always, sometimes it is better to use the point in contact with the ground or some other point. We use center of mass when it leads to simpler equations than the other points. In problems dealing with torques or rotations we use the theorem T: the sum ...

2

Partly because the magnitude of the gravitational force decreases as $\frac{1}{r^2}$, so as the distance from the center of the earth, $r$, increases, the magnitude decreases. The bigger reason for spacecraft is because they are constantly in free fall, and there is no way to feel gravity when you are falling freely. The spacecraft are falling and moving ...

2

I've never been at a theme park where you can mount into a plane at free fall. The photo that you posted is inside a reduced gravity aircraft. So you don't modify gravity, you are just falling.

3

The only way to do it is to put you temporarily in free fall. But as for the room you describe, I can only think of one type. Bring a scale with you next time you go down an elevator, and watch artificial gravity reduction at work! Heh heh.

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