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23
votes
16answers
8k 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 ...
20
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 ...
18
votes
10answers
34k 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
2k 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 ...
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 ...
13
votes
3answers
624 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 ...
12
votes
2answers
1k 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?
10
votes
3answers
829 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 ...
8
votes
4answers
5k 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 ...
8
votes
1answer
337 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 ...
7
votes
1answer
112 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

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
3answers
96 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
834 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
353 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
6answers
5k 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? ...
4
votes
3answers
336 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
687 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

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
229 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
173 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
2k 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
16k views

Does a weighing machine 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?
3
votes
1answer
6k 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 ...
3
votes
2answers
629 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 ...
3
votes
1answer
89 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
346 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
46 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
6k 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?
2
votes
4answers
2k 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 ...
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
312 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
103 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
2answers
169 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
2answers
323 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. Thank you in advance for your help!
2
votes
6answers
5k 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 ...
1
vote
3answers
11k 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
3answers
479 views

Forces on an aircraft - thrust, lift, drag, weight

I'm extremely sceptical about the wikipedia page on aircraft flight mechanics. When describing 'straight climbing flight', it says: lift is unable to alter the aircraft's potential energy or ...
1
vote
2answers
270 views

What's the weight of the earth?

What's the weight of the earth? That is, what's the weight of the earth in the gravitational field of the sun? I imagine it's either $0$, because there's no net fall toward the sun, so the downward ...
1
vote
4answers
88 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" ...
1
vote
3answers
109 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?
1
vote
3answers
3k views

If something weighs 25 kg, how do I find the mass of the object?

An object is falling and it weighs 25 kg (on a scale, presumably). What is its mass? I know that weight is measured in Newtons and mass in kilograms, but what if a problem states that something ...
1
vote
3answers
75 views

Scale on an elevator

When you are accelerating upwards in an elevator, you feel an increase in apparent weight. A scale measures the total amount of force pushing down on it, and if you were to step on a scale in an ...
1
vote
1answer
61 views

Kettlebell squats center of mass

I should, first of all, state that I have very limited knowledge of physics but as a fitness enthusiast the following question has puzzled me for a while. When I do squats on the gym holding a ...
1
vote
1answer
91 views

Making a superadjustable barbell

My working knowledge of physics is the level of a 7th grader (if I'm lucky) so please excuse this probably totally stupid question, but my curiosity is greater than my shame: Would it be possible to ...
1
vote
1answer
4k views

Floating Objects and Weight

The Situation: A ball is placed in a beaker filled with water and floats. It is also attached to the bottom of the beaker via a string. The Question: The ball is attached to the beaker, thus ...
1
vote
2answers
72 views

Why is sometimes more difficult to lift a baby?

I have a small cousin and she enjoys when I pick her up, which I can do pretty easily. Sometimes though she decides she wants to make my life difficult, and when she decides so, she tells me she is ...
1
vote
2answers
74 views

Weight of a mass falling into an open container which is closed after the mass goes inside it

Consider a container with lid of total mass, $M$. A mass, $m$, is allowed to fall into the container when the container is open. The whole set up is kept on a sensitive weighing machine and everything ...
1
vote
1answer
309 views

Do different density objects in liquids affect net weight [duplicate]

I would test this but I have no tools to test it with. If I have a beaker of water and weigh it on a measure. Then I stick my fingers in the water (it doesn't over flow) does the weight change or ...
1
vote
1answer
64 views

Generating forces precisely [closed]

When we like to produce known forces, we know that standard weights acting vertically on a object creates a known force. Now, what are the other methods to generate forces with accuracy? It is a 'do ...