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24
votes
17answers
9k views

Doesn't a box holding a vacuum weigh the same as a box full of air?

This was recently brought up, and I haven't been able to conclude a solid answer. Let's say we have two identical boxes (A and B...
22
votes
7answers
7k views

Where on Earth does the mass of 1 kg actually produce a 1 kg reading on a digital scale?

Gravity on Earth varies by about 0.1% between poles and equator. If someone was buying/selling something mass critical e.g. gold, where is the standard place on Earth where a 1 kg mass produces a 1 kg ...
19
votes
2answers
2k views

What is the weight equation through general relativity?

The gravitational force on your body, called your weight, pushes you down onto the floor. $$W=mg$$ So, what is the weight equation through general relativity?
18
votes
10answers
102k views

What is the difference between weight and mass?

My science teacher is always saying the words "weight of an object" and "mass of an object," but then my physics book (that I read on my own) tells me completely different definitions from the way ...
18
votes
7answers
3k views

Does the weight of an hourglass change when sands are falling inside?

An hourglass H weighs h. When it's placed on a scale with all the sand rested in the lower portion, the scale reads weight x where x = h. Now, if you turn the hourglass upside down to let the sand ...
14
votes
3answers
892 views

What limitations are there in measuring physical properties accurately?

In a StackOverflow answer, I attempted to explain why a 32-bit float was perfectly adequate for representing the questioner's weight measurement: Physical properties are inaccurately measured ...
13
votes
2answers
1k views

An atomic bomb explodes inside of an “unbreakable” container which is on a scale. Does the “weight” of the container change?

I read that most of the "mass" in the proton was actually energy from the quarks and gluons, as opposed to the actual mass which was coupled to the Higgs field. This made me start thinking about ...
10
votes
3answers
1k views

How can I weigh liquid in a sealed container?

How do you measure the mass and volume of alcohol if it is in a sealed container? Are there clever ways of achieving this? The weight of the container is not known. I can't open the container, I can'...
10
votes
1answer
499 views

A flying fly inside a sealed box on a scale

suppose there is a scale able to measure weight with an uncertainty of $10^{-9}kg$ . On the scale, an airtight plastic chamber is placed. Initially, a fly of mass $10^{-5}kg$ is sitting at the bottom ...
8
votes
4answers
6k views

When we do pull-ups , does the bar takes more weight than when we hang down on the bar?

When I do pull-ups, I feel I push down to the bar. But does the bar really take more weight than just hang down? For people who don't know pull-ups and hang down, here is an illustration. Left: Hang ...
7
votes
1answer
136 views

Why does the heaviest point on a spinning ball tend to become the topmost pole? [duplicate]

I have a mostly hollow, small clear plastic ball. Inside the ball is a weight stuck to the edge but the weight is smaller than the ball so the ball will always come to rest with the weight at the ...
5
votes
4answers
2k views

How do astronauts measure weight/mass on other planets? [closed]

At the start of The Martian movie the astronauts collect samples, targeting for "100 grams". Hence the question ... what units do astronauts actually use? I did some quick google search but all I get ...
5
votes
4answers
3k views

Why do we weigh less when falling?

I don't want to go to science world to find out because it would be a long round-trip. I understand that acceleration/deceleration would effect the weight and I can also imagine that someone at ...
5
votes
6answers
15k views

Is a block of cotton heavier than a block of iron?

if i have a block of cotton and a block of iron each containing a weight of 100 kg when measured on a weighing machine, in reality which one is heaver than the other, which one is heavier and why? ...
5
votes
1answer
18k views

Calculating electric motor's weight lifting ability knowing power. What else do I need to know?

So, my company works with electric motors, and my boss wanted me to calculate how much weight could be lifted by a motor rated at 750W. I know that I can't just calculate the work done by it without ...
5
votes
3answers
129 views

Walking on water

I was wondering about walking on water. I wonder if we can use surface tension to do this. Lets say I make a pair of shoes in shape which has infinite perimeter (e.g a koch snowflake) with glass. Now ...
5
votes
2answers
2k views

Difference between weight of water and pressure of water

(I didn't even have a basic formal education in physics. I'm learning through the internet out of my own interest, so if there are any silly mistakes, kindly bear with and guide me through.) ...
5
votes
1answer
398 views

How much does a proton weigh when it is going around the LHC at CERN?

Considering that speed increases weight and the proton is going at almost the speed of light, I would like to know how much a speeding proton would weigh in the LHC.
4
votes
3answers
20k views

Why do we use kilograms instead of newtons to measure weight in everyday life?

What was the reason to use kilograms to measure weight (e.g. body weight, market vegetables etc.) instead of using newtons?
4
votes
3answers
383 views

Can I do something for being heavier to be lifted?

Playing with a friend, one started to try to lift the other, and then the other way back. We started to talk about "making some force" to be more difficult to lift - one could think about having more ...
4
votes
3answers
2k views

Can mass be directly measured without measuring its weight?

From Wikipedia, http://en.wikipedia.org/wiki/Mass Inertial mass measures an object's resistance to being accelerated by a force (represented by the relationship F=ma). Active gravitational ...
4
votes
2answers
1k views

When you breath in a helium balloon, do you lose weight?

We all know the trick of breathing in a helium balloon to get a funny squeaky voice! When you do this, would it be correct to say you lose weight? On the one hand, the helium should make you more ...
4
votes
2answers
2k views

Does the weight of fluid in a conical container act entirely on the base?

Scenario description Lets assume both containers have a capacity of 300 litres. One is a vertical tube as shown in pic 1 Other one is more or less a V shaped containers as shown in pic 2 Both are ...
4
votes
3answers
441 views

Why does the air pressure at the surface of the earth exactly equal the weight of the entire air column above it

Why does the air pressure at the surface of the earth (resulting from collisions of molecules on the surface of the earth which has to do with the velocity of the particles) exactly equal the weight ...
4
votes
1answer
180 views

Need to weigh a sack of kittens

Hypothetical brain teaser here, no real kittens involved! - For some bizarre reason I have a sack of kittens, I need to find the total weight of the kittens and the sack but I'm only allowed to use ...
4
votes
2answers
3k views

Place each foot on a scale: can you add the two to find your weight?

I frequent a blog from a British psychologist, and every Friday he likes to pose an interesting puzzle or riddle. The Monday after that he posts the answer. They're good fun, and IANAP but this week's ...
4
votes
2answers
24k views

Does a scale measure weight or mass? [closed]

What does a measuring scale measure: mass or weight? I mean, when we stand on a weighing scale the reading we get is in $\mathrm{kg}$'s. What does this mean?
4
votes
1answer
207 views

Why is the apparent weight smaller when you crouch down on a scale?

I am having a problem understanding the concept of the apparent weight change when you crouch down, stand up, and jump on the scale. What is happening that makes the scale change?
3
votes
4answers
513 views

What truly is mass, and is there a direct way to measure it?

We know a mass of an object of one kilogram as an object that weighs W = mg = 9.8 N and we reference it to that, (when it should as a fundamental parameter describe weight not the opposite). But if we ...
3
votes
3answers
73 views

Fluid mechanics paradox: The force needed to 'balance' a fluid using a piston

We know that the pressure in a fluid (like water) is dependent on the depth. Consider this example: For the first setup, solving the pressure at the bottom yields $P_1 = \rho gh = 1000kg/m^3 \bullet ...
3
votes
1answer
174 views

Feathers and Human Flight

In the case of Angels where they're supposed to have wings full of feathers and can fly. If we created a flight suit for humans made out of feathers, how big would the feathers have to be? If the ...
3
votes
2answers
581 views

How much work will a human do to lift a weight?

I saw a pretty simple homework question here that asked how much work it takes to lift a 200 kg weight, and while the math for a basic answer is simple the weightlifter in me instead wanted to ...
3
votes
1answer
95 views

Do we feel 0.4% less body weight on mount everest?

Weight of the object at surface of earth(where $g=9.8066$). considering Weight=$100~\rm kg$ ,Weight ($W_1$)=$mg$ , mass=$10.1972~\rm kg$ At mount Everest top: Height of Mount Everest = $8.848\rm km$...
3
votes
1answer
62 views

Do we weigh more when standing near massive buildings?

I'm very new to the concepts of SR/GR and curvature of spacetime. My understanding is that the bending of spacetime is the causation of gravity, and that matter is the causation of the bending of ...
2
votes
3answers
268 views

Would a person gain or lose weight after expelling a flatus?

Considering the chemical composition, mass, and pressure range of typical human flatulence, would a person gain or lose weight after passing gas?
2
votes
2answers
1k views

What is the weight of the Philae lander on the Churyumov–Gerasimenko comet compared to earth?

We know the payload mass of the Philae lander was 21kg. We know the mass of the Churyumov–Gerasimenko comet is roughly 1 x 10^13kg. We know the mass of Earth is roughly 5.9x10^24kg. I've heard ...
2
votes
2answers
1k views

Weight versus gravitational force [duplicate]

What is the difference between weight and gravitational force? I am a beginner who want to study physics properly.
2
votes
1answer
114 views

How to weigh your nephew [closed]

My nephew is 3 and weighs around 30 pounds I am guessing. However, I would like to weigh him at home. I have kitchen scales, one flat one that goes up 1kg and one that looks like this picture that ...
2
votes
1answer
34 views

Does a degassed magnet weigh less than one that is not?

I learned matter with an electric current weighs more than matter with no current. Does that apply to magnetic material in the same way but with it's magnetic fields instead of electric current? A ...
2
votes
2answers
233 views

When “weight” of an object is listed, is it really the mass or the weight?

I Have read an earlier post regarding this, but the answer wasn't perfect enough or I didn't understand so! Let me put it to clear, I know difference between weight and mass. Also I know the ...
2
votes
1answer
136 views

Confused by gravity and weight [closed]

I know that $F = mg$ so $2,00 \textrm{ KG m} \cdot 9,81 \textrm{ N g} = 19,62 \textrm{ N F}$ Why does my book say that the weight of a $2,00 \textrm{ KG}$ object is $19,62\textrm{ N}$, the mass is $2,...
2
votes
2answers
3k views

Is there a difference between Weight and Force of Gravity?

Is there a difference between Weight and Force of Gravity or they just mean the same thing? My textbook does not clarifies this point.
2
votes
7answers
13k views

Trouble understanding the concept of true and apparent weight

I need help understanding the concept of true weight vs apparent weight. I understand this much: if someone is standing in an elevator on a scale, the further up they go the less the reading on the ...
2
votes
2answers
47 views

Exertion of force due to spin of Earth

If Earth were to spin at a different speed would I be experiencing a different weight?
2
votes
1answer
64 views

Applying downward force on someone without adding to their weight

I am creating a scenario for a superhero comic, and need help with an idea. I'd like the solution to be based in scientific theory, or at least scientific fantasy, as opposed to resorting to simply ...
1
vote
2answers
235 views

When referring to weights and mass of weights in a physics laboratory, do we use the term mass or weights?

What terminology is used to refer to weights/ mass/ weight of mass/ mass of weights when referring to the mass of weights in a physics report? My question is more of the weights that we use in the ...
1
vote
5answers
6k views

If you are on Earth, are your mass and weight the same?

I was wondering how mass and weight are different so I Googled it. I found that mass is constant no matter where you are because it is the amount of matter in an object and weight changes because it's ...
1
vote
5answers
5k views

What makes water heavier than air?

I apologize in advance if this is too basic for this site. Considering that hydrogen is lighter then oxygen, and water is 2/3 hydrogen, and only 1/3 oxygen, and our "air" is comprised mainly of ...
1
vote
5answers
20k views

Why does cold water weigh more than hot water in a fixed volume?

Take a bucket of hot water and the other bucket of cold water. Why does the bucket full of cold water weigh more than bucket full of hot water?
1
vote
5answers
154 views

Reduced-gravity flight (A300 0-G): what is actually reduced?

I doubt I can hide from the effects of gravity when I'm close to Earth. We usually don't question this biker is fully experimenting gravity: Source. But with the well-known "reduced gravity" ...