What is Weighing: Definition and 91 Discussions

In science and engineering, the weight of an object is the force acting on the object due to gravity.Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar quantity, the magnitude of the gravitational force. Yet others define it as the magnitude of the reaction force exerted on a body by mechanisms that counteract the effects of gravity: the weight is the quantity that is measured by, for example, a spring scale. Thus, in a state of free fall, the weight would be zero. In this sense of weight, terrestrial objects can be weightless: ignoring air resistance, the famous apple falling from the tree, on its way to meet the ground near Isaac Newton, would be weightless.
The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton. For example, an object with a mass of one kilogram has a weight of about 9.8 newtons on the surface of the Earth, and about one-sixth as much on the Moon. Although weight and mass are scientifically distinct quantities, the terms are often confused with each other in everyday use (i.e. comparing and converting force weight in pounds to mass in kilograms and vice versa).Further complications in elucidating the various concepts of weight have to do with the theory of relativity according to which gravity is modeled as a consequence of the curvature of spacetime. In the teaching community, a considerable debate has existed for over half a century on how to define weight for their students. The current situation is that a multiple set of concepts co-exist and find use in their various contexts.

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  1. C

    I Error on a weighing scale due to wrong size

    If you have say a 15 centimetre long piece of rigid plastic and the weighing scale's tray is only 10 centimetres, what is an estimate of the error that introduces in the measurement assuming the weight is still within normal parameters for the weighing scale. I was wondering what the approximate...
  2. lionpauu

    A Do moon phases affect weighing precision on the microgram range?

    Hi, I'm looking to improve the precision of a system over a several hour cycle of operation of +50°C operation. The mass is ~11g and is suspended below the balance via a factory provided point. The "sample" is enclosed within a large borosilicate flask 150mm dia x 450 mm height that is trace...
  3. F

    I Can Gas be Weighed in a Vacuum?

    Is it possible to weight a gas in a container surrounded by a vacum? I am arguing with flat-earthers on how gas weight is determined. I just assumed that you can weigh a gas by placing it in a container on a scale inside a vacum. I think this was wrong. Can you do this or must you weight gas...
  4. mopit_011

    Halliday Resnick Krane Example Problem: Uncertainty on Weighing Machine

    In the solution to the example problem, they wrote the following statement. “The least significant digit is the units digit, and so your weight is uncertain by about 1 pound. That is, your scale would read 119 lb for any weight between 118.5 and 119.5 lb.” I don’t understand why the scale...
  5. S

    Weight of gold chain when dropped on a weighing scale

    The force exerted downwards on the scale by the chain when it is kept on it would be Fg= Mg =λLg where λ is the linear mass density However when the chain is dropped onto the scale it exerts an additional force due to its change in momentum The force exerted by each part of the chain would...
  6. rudransh verma

    B How do mechanical (weighing) scales work?

    I want to understand how the weight machines work that we use in homes and shops. I have been working on force and motion chapter and I was curious how this weight machine actually push up and how it applies force to the feet of the person being weighed? What reading is this that we see in...
  7. S

    Most accurate scale for weighing objects

    Hello, What is the most accurate weighting scale in existence and what kind to look for if you want accuracy. The other day I got this scale. I put a known 7.6 pound book. It showed up as 7.730 lbs so I returned it. I need something that can show exactly the weight. What kinds of scale must I...
  8. oldsaltysailor

    A 80 foot tree weighing 4000 pounds will soon fall on my cabin

    Homework Statement: I have a 80 foot tree weighing 4000 pounds ready to fall on my cabin. How thick of a cable or a nylon rope a do I need to stop it from hitting the cabin? Homework Equations: m=f/g I am 82 years old and can no longer do the math on this real problem I have due to a brain...
  9. jisbon

    Elevator Question: Calculating displacement from weighing scale readings

    EDIT: As per @Orodruin 's suggestion(s), I have edited my problems and equations, sorry for the confusion as I typed this out hasty. So from this question, I understand I have to find the net force for the first 10 seconds and deceleration for 20 seconds. The scale shows the force with which...
  10. R

    Solving the Weighing Balls Problem in One Weighing | Precise Scale Method

    Homework Statement Consider a set of boxes, each containing 20 balls. Suppose every ball weighs one pound, except that the balls in one box are all one ounce too heavy or one ounce too light. A precise scale is available that can weigh to the nearest ounce (not a balance scale). By selecting...
  11. DaveC426913

    B Weighing Contribution: Scatter Plot Analysis

    I have a list of people whose contribution I'm trying to analyze. Some people contribute a lot but are off-topic. Some contribute a little but are on-topic. How might I weigh them to show an accurate idea of who are the lesser value contributors? A small sample: Contributor On~topic Off~topic...
  12. E

    Friction and Scale Readings for a Cuboid on a Weighing Scale

    Homework Statement A cuboid with a mass of M is put on a weighing scale. First the situation is the one in the picture (the ball doesn't move), the cuboid stays on the cuboid without moving. What will the scale show? Now yarn number 2 is torn, the cuboid still doesn't move. What will the scale...
  13. J

    Weighing machine in an elevator

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] Initially , let the tension in spring be T Since hanging mass is just touching the weighing scale , T = 5g When elevator starts to accelerate upwards with acceleration 'a' , then on applying a fictitious force '5a'...
  14. Ravi Singh choudhary

    What will be the weighing machine's reading?

    Suppose a container is full of water is placed over a weighing machine. Now a ball is hanged with massless string but dipped inside the tank and ball is not touching the bottom. What will be the new reading on the weighing machine?
  15. donaldparida

    What will be the weight measured by the balance?

    Suppose there is a beaker filled with water placed on a weighing machine. Suppose the reading is x kg. Now, if i immerse a solid block inside the beaker without touching the walls or the bottom of the beaker, will the reading given by the weighing machine increase or not?
  16. D

    Problem with friction on weighing machine

    Homework Statement A man of mass ##80## kg, stands. on a horizontal weighing machine, of negligible mass, attached to a massless platform P that slides down a ##37^{\circ}## incline. The weighing machine reads ##72## kg. Man is always at rest w.r.t weighing machine. Calculate: (a) The...
  17. P

    B Do I weigh 50 kg or 50 * 9.8 kg?

    When I take my weight, it often shows around 50 kg. However, in my Astronomy class currently, it was mentioned that an average person's mass is roughly around 50 kg. So, which one of them is correct? It doesn't make sense for my weight to be 50 kg because kg isn't exactly a unit of force, but...
  18. Kernul

    Weighing a Man on the Equator: Solving the Puzzle

    Homework Statement A man that has an ordinarily weight of 780 N stands on a libra on the equator. Homework Equations What is the weight measured by the libra? The Attempt at a Solution I thought it was simple, so I just did: P = m * g Since it gives me P I can simply do: m = P / g = 780 /...
  19. tanmay

    Why is air pressure force not considered while weighing?

    we know that air pressure on our Earth is 1 atm. Also 1 atm = 10^5 P Also we know Pressure(P) equation = P = F/A So, F = P*A So if small area(A) in which we are standing is also taken then pressure force is that area(A) times 10^5(Atmospheric pressure in Pascal) i.e 10^5*A So why don't we...
  20. P

    Weighing with A 400 N Scale and 80 N Spring Dynamometer

    Homework Statement A former student of mechanics wishes to weigh himself but has access only to a scale A with capacity limited to 400 N and a small 80 N spring dynamometer B. With the rig shown he discovers that when he exerts a pull on the rope so that B registers 76 N, the scale A reads 268...
  21. R

    An advanced two spring weighing machine

    Homework Statement A more sophisticated weighing machine contains two springs. The effect of these is that the machine is more sensitive to masses less than some fixed value M0 than it is to greater masses. The equilibrium displacement is alpha1*M when M<M0, and (alpha2+c) when M≥M0 , where...
  22. T

    Weighing Ourselves: lbm or lbf?

    I'm sure this has been asked before but it's annoying me. When we weigh ourselves is it in lbm or lbf? Because we weigh different on say, the moon, our weight must be lbf right? But if I weigh 150 any unit converter will say I weigh 68kg. Or do I weigh 2.13kg? Can I say I weigh 21 Newtons...
  23. N

    Weighing a bowling ball project

    In bowling, the ball will have a heavy spot marked as the center of gravity (cg). This will have an additional 1oz to 5 oz of weight to compensate for when the fingers are drilled into the ball. In bowling a dodo scale is used to measure the difference in static weight of the bowling ball...
  24. S

    Dark matter and weighing galaxies

    Hello I have a question (well its 2 questions)... I'm not hugely knowledged on the subject so i tend to question things in a more ignorant way but i wanted to know two things: Firstly, how do astronomers weight a galaxy at an accurate level to be confident enough to say there is more stuff...
  25. K

    If we could put Earth in a weighing machine

    ... regardless of any possible technical problems, and then, on earth: a) someone throws an object in the air and it falls b) someone puts an object to float in a magnetic field generated by an artificial magnet that lays on earth In situation A I think the weight measured would...
  26. C

    Engineering Weighing the Pros and Cons of a Mechanical Engineering Career

    I am thinking about being a mechanical engineer but there are a few things I wanted to take into account before I picked this field. First, the amount of available jobs is important. Second, salary. I'm not a money crazed person but I plan on raising a family. I want to be able to pay...
  27. P

    Can a Linear-Coil Spring Improve the Accuracy of a Weighing Machine?

    Project: Weighing machine based on potentiometer Principle: On changing the length of the wire current in the circuit will change which will change the deflection in the ammeter Set up: On top of four or three spring(same spring constant) a board is attached so when a weight is kept on top...
  28. T

    Programs Weighing Major Options for R&D

    Although I asked a similar question two days ago, I'm still seeking an (biased would be nice) answer. So far Physics major seems like the right choice, Physics is still my passion. But, there are always "buts", I would like a major more applicable in the real world. My major choices are...
  29. F

    Calculating acceleration of a plane weighing 9800N

    Homework Statement Calculate the acceleration of a plane weighing 9800N when the forward force is 210000N, the drag force due to air resistance is 500N Homework Equations F=ma The Attempt at a Solution the mass is 1000kg as 9800/9.8 is 100. The resultant force R must be...
  30. H

    Chain falling on weighing scale-find total reading

    Homework Statement A chain of length l, mass M falls on a weighing scale vertically down. We need to find the reading of the scale when a length 'x' has fallen on the scale. Homework Equations F= dP/dt W=Mg dm= (M/l)x dm/dt=m(v^2)/l The Attempt at a Solution So initially, I...
  31. jbrussell93

    Weighing my options: EE & Physics

    After a year of engineering undergrad, I'm finally beginning to figure out what exactly I want to do. I'm a biological engineering major and have been debating switching to physics and/or engineering for about a semester now, and the time is a approaching to actually make a decision. I'm...
  32. F

    Weighing yourself on a solid surface vs carpet

    Recently I started thinking about it, because apparently you get different results. At first, I thought you would weigh less on a carpet (according to the scale), because the carpet supports some of your and the scale's weigh. But thinking deeper into it, I actually figured it shouldn't make a...
  33. I_am_learning

    How Can the Weight of a Human Head be Measured?

    Just in the middle of random discussion with my friend, we wondered how could the weight of a human head (the portion above neck) be measured? Of-course without doing nasty things. (eg. chopping. :devil: )
  34. W

    Medical Weighing Pros and Cons of Laser Surgery for Myopia

    I've been mulling over whether or not to undergo laser surgery to correct my vision. Myopia set in when I was 12 and has gradually become worse (~ -3.75, 4 now). Being rather active, I find glasses to be a big pain because they get in the way often, sometimes even leading to injury. I was...
  35. H

    12 rubies weighing problem/riddle

    i searched for this one if it is posted before, apparently not, but if it is, sorry for that. a merchant has 12 identical rubies with equal masses that he wants to put on display, however, he knows that one of these rubies is special in the sense that its either heavier or lighter than the...
  36. A

    What weight does our weighing machine show?Is it the mass or weight(mg)?

    What weight does our weighing machine show?Is it the mass or weight(mg)?
  37. H

    Weighing the Opportunity Cost of Going Back to School for CS

    I graduated a year ago. I picked the wrong major (IE/OR), so I'm considering going back to get the "right" major within two years (CS). This translates into a opportunity loss of two years of salary (80k post tax for both years) and 20k in educational expenses per year (40k total). And that's...
  38. D

    Why does a warm weighing cup weigh less?

    One of my jobs at work is to determine the amount of oil and grease present in wastewater samples. In the beginning of the procedure I usually take a tray of oil and grease cups out of a 125 degree oven and place it in a desiccator for roughly an hour before weighing on a balance. After...
  39. M

    Weighing Options: Should I Take AP Stats?

    Hi, I'm deciding whether or not to take AP Stats. I will be taking Honors Physics and AP Calculus AB and AP Latin. I've read that only Calculus-based stats is useful for Engineering. I don't want to take all three courses because I don't want to kill myself. Is AP Stats absolutely...
  40. U

    How much torque is required to move an object weighing 150lb?

    How much torque is required to move an object weighing 150lb?Torque is required to move an object weighing 150lbs. Its not a homework question, I'm trying to build an electric scooter but I have not yet reached high-school or taken any advanced mechanical engineering classes or any at all for...
  41. A

    How Does a Weighing Machine Measure True Weight?

    My book says that a weighing machine measures the normal reaction to us from the surface we are standing on... So, I basically have 2 doubts here: (1) In Resnick, Halliday and Walker 6th edition (chapter on Laws of Motion), weight is defined as the magnitude of the force required to body a body...
  42. A

    Reading on a weighing scale

    Reading on a weighing scale... Homework Statement Two vessels have the same base area but different shapes.The first vessel takes twice the volume of water that the second vessel requires to fill up to a particular common height. IS the force excerted by water on the base of the vessel same...
  43. A

    Weighing Trouble: Find the Set with 5kg Balls

    suppose you have 10 sets of balls containing 10 balls each. out of these 9 sets have all balls weighing 10kg (individually) and 1 set has 5kg balls. You can use the digital weighing machine once. how will you wind out which set has 5kg balls?
  44. M

    Weighing fluids with immersed objects

    So imagine that in an open room you have a big scale and on it you have a jar and a lid sitting next to each other. Imagine a butterfly floating into the jar but not touching the bottom. I wouldn't think this would increase the reading on the scale. But if you put the lid on the jar, closing the...
  45. P

    Weighing an Object in Water: Does the Bouyant Force Matter?

    if i place a weighing machine at the bottom of the swimming pool and then put a box on it whose density is greater than the iquid , then will it weigh more or less , as compared to on the land ? i think that it will weigh less , but if its lower surface is in contact with the surface of the...
  46. D

    Mass of chair on weighing scale and wall

    For what it's worth, I came up with this problem, so perhaps it cannot be solved, or there could be a way to solve it without using all of the information given. Homework Statement A chair rests on a weighing scale and a wall. The relevant surfaces of the scale and the wall are...
  47. Q

    Why Does Gravity Affect Weight?

    Hi. I'm an absolute noob at physics, so I went to the library and checked out a couple beginner books. Basic Physics: A self-teaching guide and Science 101 Physics. I'm just getting started reading physics 101 and read the following statement: "...all you have to do to determine your...
  48. P

    Weighing Something in an Elevator

    If you were to way an object on a Newton spring scale in an elevator, when would the scale display the largest number? elevator moving up moving down no affect In my opinion, an acceleration in the elevator would be required, as that would unbalance the forces and was traveling at a...
  49. E

    Tensions in Suspended Ball System: Solving for Horizontal and Angled Cords

    Homework Statement A ball weighing 100-N is shown suspended from a system of cords. What are the tensions in the horizontal and angled cords? Homework Equations F=ma The Attempt at a Solution I tried to use F=ma but I couldn't go anywhere with the equation. I know that sum of Forces...
  50. S

    Weighing a Salmon in an Elevator: What's the Apparent Weight?

    Homework Statement A 5.0kg salmon is weighed by hanging it from a fish scale attached to the ceiling of an elevator. What is the apparent weight of the salmon if the elevator is (a) at rest, (b) moving upward at 2.5 m/s2, and (c) moving downward at 3.2 m/s2? Homework Equations Sum of F...