Weighing Definition and 91 Threads

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. E

    Force of 6" x 18" Steel Panel Weighing 3.25 Pounds Striking a Person

    This topic has been discussed before at this site, but there was never any agreement. I have a very specific situation that I hope I can get a concrete answer, including equations and a step-by-step solution in inch/pounds/seconds units. A steel flat panel 6" X 18" weighing 3.25 pounds...
  2. W

    Concrete block weighing 20,000 lb is supported by 2 STEEL rods

    a concrete block weighing 20,000 lb is supported by 2 STEEL rods, rod AB has an area of 1 in and rod CD has an area of 2 in... what is the elongation of each rod...? http://s44.photobucket.com/albums/f46/maximus11373/?action=view&current=untitled.jpg&newest=1i don't know how to start, should i...
  3. Q

    Dropping meat on weighing scale

    hi, if we drop a piece of meat say 1kg from 1m above the plate, on a plate 2kg, and the plate is on a weighing scale of spring F=kx, how do we find how much the spring will first compress? ( not referring to the equilibrium where total weight = spring force) so we can't use F=kx = mg here...
  4. N

    Two men want to carry a wooden beam weighing 200

    Not sure about this one, any help? Two men want to carry a wooden beam weighing 200 lbs which is 20 feet long. Both men are equal height however one is stronger than the other and wishes to bear 50% more the weight. How far from the end of the beam should both of the men be to make this possible?
  5. I

    A piece of iron weighing 85.65 grams was burned in air.

    Homework Statement A piece of iron weighing 85.65 grams was burned in air. The mass of the iron oxide produced was 118.37g. 1. Use the law of conservation of mass to calculuate the mass of oxygen that reacted with iron. 2. use the molar mass of oxygen to calculate the number of moles...
  6. J

    Help (required force to move a sliding door weighing 100 kg with two rollers)

    what is the required force to start moving a sliding door weighing 100 kg with two rollers. what are the forces acting on the system? shall i used rolling friction on this? what formula to use? thanks a lot.
  7. P

    What programming language should I learn as a beginner?

    So I just graduated from high school and am heading to college with the intention of getting a BS in physics. I took a semester of programming in Pascal my senior year, but had to drop the class the second semester (to get a freakin' art credit to graduate. God**** arts...), so I didn't learn...
  8. T

    Weighing a Ladder While Leaning Against a Wall?

    Lets say you take a ladder and put it on a scale and measure it's weight while balancing it vertical. If you then lean the ladder at varying angles against a wall, would the scale's reading remain unchanged? I take it that it would, but for some reason this seems odd to me. Lets say the...
  9. T

    Weighing yourself in the elevator

    Need help:Weighing yourself in the elevator-acceleration problem Homework Statement If you stand on a spring scale in your bathroom at home, it reads 600N, which means your mass is 60kg. If instead, you stand on the scale while accelerating at 2 m/s^2 upward in an elevator, what would the...
  10. U

    Iron ball in water, reading on weighing machine

    What is the reading on the scale for the first one?? My friend mentioned that upthrust need not be considered as its an 'internal force', i wonder why?? Shouldnt' the net force dowards be (Weight of stone - pVg) + (Weight of water + pVg) as the water experiences an equal an opposite downthrust...
  11. wolram

    Weighing Public Opinion vs. Global Impact: Examining Unproved Theories

    How much weight if any, should be given to public opinion to scientific theories that are, let's say difficult to prove, and could have significance effects globally.
  12. D

    Is Your 42 kg Scale Reading Accurate in Different Gravitational Fields?

    if our weight is 42 kg in a weighing machine , in reality is it more or less than 42 kg?
  13. W

    Weighing the Box with Bees Inside - Who's Right?

    A coworker and I were passing time by asking stump the idiot questions. He asked the following question. "If you had a box that weighs five pounds empty and placed five pounds of bees inside the box and then shook the box to make all of the bees take flight within the box what would the box...
  14. C

    Calculating dF/dθ for a Crate Weighing 150 lbs at θ=30°

    Homework Statement The force F (in pounds) acting at an angle θ with the horizontal that is needed to drag a crate weighing W pounds along a horizontal surface at a constant velocity is given by F= (μW)/(cosθ+μsinθ) Where μ is a constant called the coefficient of sliding friction between the...
  15. Cyrus

    Weighing the Cost of Fixing Your 10 Year Old Car

    At what point do you say spending x amount of money on fixing your car isn't worth it anymore? My 10 year old accord needs the front axle fixed, $300. And my radio is busted, so I bought a new head unit w/all wires for around $90.00. I couldn't take not having a radio anymore :rolleyes...
  16. R

    Undergraduate Research: Weighing the Options

    Please tell your opinion with reasons (if possible). I hope this will be important for those who do not have a good undergrad research experience Please consider all the factors including the demand, funding, research, jobs,...etc.
  17. X

    Spot the Odd Ball: Weighing Challenge in 3 Chances

    You have 12 balls, and a weighing machine with no standard weighs. One of those 12 balls is either lighter or heavier than the others. Spot the ball in 3 chances with the weighing machine.
  18. S

    How Can You Weigh a Ship Without a Scale Using Fluid Dynamics?

    so your company has built an enormous ship and it is being lowered into a large pool to test if it can float... another company has contacted you to buy your ship and they want to know how much the ship weighs... your company has spent all its money building the ship and you can't afford a...
  19. B

    Schools 21-Year-Old Security Guard Weighing Online Physics/Math Degree Options

    im 21 and curently a security guard. my dad go hurt and i had to get a job straight out of high school to help support my family doing so putting my education on hold.My question is if the Bachelor of Science (BS) in Interdisciplinary Studies - Math and Physics at Ellis College online would be a...
  20. D

    Something interesting about magnets and weighing scales

    Hi, I got hold of a set of kitchen weighing scales which are made of some ferromagnetic plate and my neodymium magnets. So the reading on the weighing scales increases as you bring the magnet near the weighing plate, as expected... they then reach a maximum just before you touch the magnets...
  21. X

    Weighing in on a Fluid and Thermal Engineering Test

    Hi all, I just wanted to get some peoples' opinion on a situation that recently occurred in one of my classes. This past Friday, in my Fluid and Thermal Engineering class, we had our second test of the semester. Our teacher was not there because he was out of town so a TA administered...
  22. V

    A book weighing 5 N rests on top of a table?

    This just crossed my mind. The downward force of magnitude from gravity is longer than the upward force of magnitude from the table. Which explains why the downward force of magnitude, the 5 N, comes from gravity. Am I right?
  23. L

    Weighing In on Different Planets: Radii and Mass

    Homework Statement Suppose you went to another planet having a larger radius than Earth but having the same total mass as Earth. Would this affect your weight? How? Homework Equations Not applicable...? I think. The Attempt at a Solution I don't really understand what radius and...
  24. P

    Which marble is the oddball? Heavy or light?

    i give you 12 marbles. 11 of them are identical. the 12th one looks the same, but is either heavier or lighter than the other 11. you also have a balance scale. the kind that weighs things on both sides - and if one side is heavier, it tilts down. you are allowed only 3 weighings. tell...
  25. Ivan Seeking

    Super Tonio: Baby Born Weighing 6.6kg in Cancun!

    Photograph: Elizabeth Ruiz/EPA http://www.guardian.co.uk/international/story/0,,2003489,00.html I should hope that he came by C section! Carol Burnett
  26. 0

    Weighing Laptop Options: Sony TX vs HP

    I need to get a laptop in addition to my desktop computer for doing presentations/demos and general academic use--carrying it around all day every day in a backpack while cycling/walking a few miles. I'm still undecided. I am torn between a model from Sony's TX series--unfortunately I do not...
  27. F

    Calculating Frictional Force and Time to Move a Box Across a Floor

    A box of books weighing 229 N is shoved across the floor by a force of 455 N exerted downward at an angle of 35° below the horizontal. (a) If µk between the box and the floor is 0.57, how long does it take to move the box 5 m, starting from rest? (b) If µk between the box and...
  28. P

    Finding Average Value in a Weighing Experiment

    How do you find the average value in an experiment when all it consist of is weighing a beaker and adding 10 mL of water three times to it?
  29. P

    Weighing Less in Skyscraper Lobby: What's Going On?

    The question is...Strictly speaking, you weigh less (tiny bit) when you are in the lobby of a massive skyscraper. Why is this so? I need help...I'm not asking for the answer...just some direction I'm confused because I thought the greater the distance from the Earth's center, the less...
  30. W

    Beaker with water on a weighing scale

    beaker with water on a weighing scale... A weighing scale has a beaker of water on one side and a balancing weight on the other side. You put your finger into the water carefully without touching the beaker. Will the balance be upset? Which side will appear heavier, if so? What will...
  31. M

    Weigh the Balls: Find Odd Ball in 3 Weighings

    Ýou have 12 balls. All of them have the same mass. Except one. You don't know if it weighs more or less than the other 11 balls. Your mission is to find the odd one out, and say if it weighs more or less than the 11 others. You have a balancescale. You may use it for three weighings. The...
  32. G

    Find Faulty Coin: Weighing Balance Challenge

    you have 9 coins. one of these coins is faulty, that is it is either heavier or lighter than the rest. you have a weighing balance. in thre weighings you have to find 1. which is the faulty coin and 2. is it heavier or lighter.
  33. G

    Find the sensitivity and accuracy of electronic weighing scales?

    How would I find the sensitivity and accuracy of electronic weighing scales?
  34. M

    Why is Weighing Liquids More Accurate than Measuring w/Cylinder?

    i want to know Why sometimes is it more accurate to weigh liquids than to use a graduated cylinder to measure them??
  35. G

    Weighing Mass of Photons in Different Directions

    So, I'm having trouble with the concept of the mass of a "system" being greater than the sum of the masses of the components of that system. Specifically in the case of photons. A system consisting of 1 photon has no mass. A system consisting of 2 photons in the same direction has no mass...
  36. G

    What is the maximum number of bags that can be identified with 3 weighings?

    Perhaps some of you have seen this before A scale will report the difference, in grams, between the masses on the two sides, as well as telling you which side is heavier. So if you place 25 grams on the left pan and 27 grams on the right, you find out that the right side is heavier by 2...
  37. J

    Thermodynamics - Weighing an aquarium

    Hey.. had a problem which am tryin to solve... During an ecology experiment, an aquarium half filled with water is placed on a scale. The scale reads 195N. a) a rock weighing 8N is added to the aquarium. If the rock sinks to the bottom of the aquarium, what will the scale read? b) The...
  38. S

    Solving Two Physics Problems: Weighing Rocks and Steel Barbells

    Alright, these two problems are driving me nuts: 1. ---To verify her suspicion that a rock specimen is hollow, a geologist weighs the specimen in air and in water. She finds that the specimen weighs twice as much in air as it does in water. The solid part of the specimen has a density of...
  39. Math Is Hard

    How can you accurately measure your weight on Jupiter without a solid surface?

    This was a bonus question on my astronomy homework, but my knowledge of basic physics is so incredibly limited that I am really struggling with it. It's bugging me because I'd just really like to know how this works. "Given that Jupiter has no solid surface, how could you weigh yourself on...
  40. G

    Can Graviton Mass Be Calculated Using Universal Constants?

    "Weighing the Graviton" 9^9 (387,420,489) Combinations/Equations http://physics.nist.gov/cuu/Constants/ [UPDATED 1998 CODATA-NIST VALUES] The Primary Universal Base Unit Values 1) mass… (hc/G)^1/2 = 5.4563026(39) x 10^-8 kg 2) length… (hG/c^3)^1/2 = 4.0507625(38) x 10^-35 m 3) time…...
  41. H

    A man weighing 80 kg is standing on a trolley weighing 400 kg

    Hi all! can somebody help me out in solving following 2 questions: 1. A man weighing 80 kg is standing on a trolley weighing 400 kg.The trolly is resting on a frictionless horizontal rail .If the man starts walking on the trolley along the rail at a speed of 1 m/s with respect to the...
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