# Questions tagged [weight]

Weight is the force on the object due to gravity. DO NOT USE weight as a colloquial substitute for mass.

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12answers
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### Why don't we use weights to store energy?

One of the main reasons why we haven't switched to clean energy is the lack of efficient storage methods - But, why aren't we using dead weights to store energy and draw it back later when needed? As ...
5answers
12k views

### Do the weights of two liquids not add when mixed?

I was given an interesting dilemma today. A co-worker saw me adding a liquid (Diisopropyl ethylamine AKA DIPEA) to a flask filled with another liquid (Tetrahydrofuran AKA THF). I needed to weigh out ...
19answers
28k views

### Is weight a scalar or a vector?

My professor insists that weight is a scalar. I sent him an email explaining why it's a vector, I even sent him a source from NASA clearly labeling weight as a vector. Every other source also ...
3answers
19k views

### Will helium in the tires of a bike make it lighter?

I know that helium balloons float because it is less dense than air. I'm not expecting my bike to float, although that would be pretty cool. I just wanna know if replacing normal air with helium in ...
6answers
11k views

### Why do gases have weight?

I know that a gas is made of atoms or molecules moving freely in space. When these particles hit the walls of where they're kept in they cause something called pressure. But these particles never ...
2answers
4k 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?
8answers
21k views

### Will a bathtub full of water weigh more if I add something that floats in the water?

Let's say I have a bucket or something bigger, like a bathtub full of water. I weigh that bath and get some value, $x$. Then I add a small boat made of wood to that bathtub that doesn't touch the ...
13answers
15k views

### Would a gas “weigh” less than a liquid if they have the same mass?

Thought experiment: I acquired two boxes of the same dimensions and same weight. One box contains $1\ \mathrm{kg}$ of water at room temperature while the other box has $1\ \mathrm{kg}$ of water, but ...
5answers
2k views

### What is the function of this complicated tensioning system?

I saw this arrangement for tensioning overhead cables from my train window (schematic below). Why not just have one pulley wheel leading directly to the weights? What function do the additional ...
18answers
12k 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...
7answers
10k 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 ...
10answers
465k 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 ...
4answers
871 views

### Which weighs more in atmosphere, $1\,{\rm kg}$ of steel or $1\,{\rm kg}$ of feathers?

I'm having a discussion at the moment regarding the mass of $1\,{\rm kg}$ of feathers and $1\,{\rm kg}$ of steel. The person I'm arguing with states that $1\,{\rm kg}$ of feathers will be lighter ...
7answers
8k 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 ...
9answers
4k views

### How can there be weight without movement? [duplicate]

Weight is a force. Force is mass × acceleration. When I'm standing motionless on the scale, how do I have a weight greater than $0~\mathrm{N}$ when my mass is $90~\mathrm{kg}$ and my acceleration is ...
3answers
2k 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 ...
2answers
2k 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 ...
8answers
2k views

### Can a ship float in a (big) bathtub?

I am confused. Some sources say it is possible at least theoretically ( http://www.wiskit.com/marilyn/battleship.jpeg ) and some say it is not true ( http://blog.knowinghumans.net/2012/09/a-...
3answers
69k 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?
1answer
1k 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 ...
3answers
2k 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'...
4answers
12k 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 ...
6answers
42k 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? ...
3answers
1k 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 ...
1answer
179 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 ...
4answers
3k 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 ...
2answers
967 views

### Does the velocity you travel affect your weight in an elevator?

I know that if you are accelerating upward in an elevator, you will have more weight (if you are on a scale) due to normal force of the elevator pressing up into you? Would that happen if you are ...
1answer
43k 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 ...
2answers
36k views

### Does a weighing scale measure weight or mass? [closed]

When we stand on a weighing scale the reading we get is in $\mathrm{kg}$. Does it refers to mass or weight?
3answers
687 views

### Weight loss of a flashlight due to light emission

I watched this video. At one point, the man explains how a flashlight loses some mass due to light emission when turned on. OK, I get that. Then he talks about a different situation, where the ...
3answers
2k views

### Why is torque sometimes reported in kg m, instead of the usual N m?

On various websites I see torque expressed as $\rm kg\: m$, but I was always thought that torque is $\rm N\:m$ or $\rm kg\: m^2/s^2$. These are clearly not the same, so why are they called the same, ...
4answers
4k 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 ...
3answers
7k 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 ...
4answers
687 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 ...
2answers
3k 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 ...
2answers
3k 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.) ...
3answers
424 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 ...
1answer
536 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.
1answer
3k 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?
5answers
764 views

### What is the 'weight' (not mass!) of the Earth?

I am asking what might be the weight (not mass!) of the earth. My weight is the amount of force exerted on me by Earth (say 600N). So, weight of earth should be amount of force exerted on Earth by me (...
3answers
608 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 ...
2answers
4k 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 ...
3answers
2k 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?
2answers
13k 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 ...
7answers
12k 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.
1answer
202 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 ...
1answer
11k 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 ...
3answers
92 views

### What is the explanation of weight in terms of general relativity?

In GR a massive particle falls along geodesics of curved spacetime because there is no “force” on it and it has to follow straight lines. But how can the weight felt by an object on the surface of ...
5answers
35k 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?
4answers
1k 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 ...