# What is Weight: Definition and 1000 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. ### B Weight and force of gravity

A relatively simple question has been bothering me for some time: Why is the weight of an object (the force the object exerts on a surface/rope) equal to the force of gravity that the body experiences in Earth’s gravitational field? Earth’s gravitational field accelerates all bodies in its...
2. ### I Cavendish balance and mass of objects

The Cavendish balance measures the gravitational constant G. To do so requires us to know the magnitude of the smaller and larger masses in the apparatus. However, mass is derived from the weight of an object, which is the gravitational force upon an object, which in turn requires the value of...
3. ### B What forces act on a bar when you do pull-ups?

I am not sure here, even though it is probably simple. If you just hang on the bar and don't move up, you act on the bar with a force equal to your weight. But when you want to do a pull-up, I would intuitively say that you act on the bar with a higher force. But when I think about it I would...
4. ### B How Does Inclined Load Affect Weight Distribution When Moving a Cabinet?

Hello. I want to ask for advice. I know I probably won't understand it anyway, but maybe some information will help me. I did not find a solution to this problem on the Internet, which in itself I do not understand. We moved the cabinet and I can't calculate how much the weight on the opposite...
5. ### B TV Series: 3 Body Problem - affects gravitational force?

SPOILERS This obviously wouldn't happen to that extent, not without tearing the planet to pieces as well. But might they feel a reduction in weight at all? Obviously it's a pretty hypothetical question without any specifics about the distances to the suns but in theory at least.
6. ### How Does a Pulley System Affect Scale Readings?

A kid is standing on a scale and holding a rope that goes through a pulley, on the other side the rope is connected to a spring and then to a 50N mass item. Assume that the kid's weight is 700N 1. While in static mode - what will the scale show? 2. The kid is now pulling the rope to get the mass...
7. ### I Experiment on the variation of weight with temperature

Hello ! According to what I have read on the internet, the weight of a body varies with temperature, its mass remaining unchanged according to the theory of relativity. My question is what experiment is done to corroborate that the weight of a body increases with the increase in its...
8. ### Energy consumed by weight of gear on a multiday hike

I'm trying to figure out how many extra kcal I would burn on a 600km hike with a 30,000m (30km) positive gain for every additional 100g (or 1kg, whatever) of gear in my backpack. It would obviously be a quite rough approximation, as there are significant variables such as the efficiency of a...
9. ### I What is the Uncertainty in the Total Weight of a Collection of Similar Items?

Not a homework assignment. Just what must be a solved problem that I'm embarrassed I don't know how look up or figure out on my own. I want to know the total weight of a collection of N items. They are all similar but of different, unknown weights. My scale has a known accuracy of ±U units. If...
10. ### Actual Working of Weighing Machine (Normal vs gravitational force)

I couldn't think of a possible explanation.
11. ### Would one be pushing as much as their weight?

Because one is effectively pushing in the same way as a chest press machine, wouldn't the work done be the same?
12. ### Frequency & Wavelength of a Vibrating Wire

Good morning, I'm working through the problem from the homework statement above and answered it correctly, but I can't help but feel that something important is missing. I was able to correctly identify the sum of torques by using the following diagram, where the CCW rotational direction...
13. ### Inclined Plane Vector Problem: Understanding the Use of Trigonometric Functions

I'm not really asking for a solution for this problem I just want to clear up a confusion I have. Why are they multiplying the weight by the sin and cosine of the 30-degree angle? Isn't weight not affected by anything since it's constant? Also is the angle of friction 0 because it's a...
14. ### FBD of a toy car moving in a vertically horizontal circle on the underside of a dome

weight pointing down Fn pointing down and to the left (to the center of the dome) Fs pointing ..?? Should it not be off the page? Maybe up and off the page to oppose movement + gravity?
15. ### How Camera Jibs Remain at Any Angle Without Moving Counterbalances

Hi, I am trying to understand how camera jibs work. They seem to be able to remain at whatever angle despite being balanced. The counter weight is static and does not move, yet the jib does not remain level nor does lift or drops. I have spoken to the operators and they mention they don't use...

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17. ### Proving that e^{ikx} is primary with weight (h=\hbar = \alpha k^2/4)

Where ##:## really means normal ordered, in the sense that ##:A(w)B(z): = \lim_{w \to z} \left ( A(w)B(z) - \langle A(w)B(z) \rangle \right )## ##\partial X(z) = \frac{\partial X(z)}{\partial z}## How do we go form the first line to the second one?? I am not understanding it! it seems to me...
18. ### Using 18% by weight ammonium hydroxide to make 16ppm aqueous solution

TL;DR Summary: Used M1V1=M2V2 but am unsure if formula applies I feel like I could use M1V1=M2V2 but the 18% by weight ammonium hydroxide is confusing me so much. Density of ammonium hydroxide 18% is 0.926 g/cm3 18%V1=16mg/L*200L (18mg ammonium/100 mg of total solution) * V1 = 3,200mg...
19. ### The ideal weight or force to push a drill

What is and how is the estimation of the ideal weight or force to push (bit being in) a driller down when drilling (stainless) steel to bore 3-9 mm hole?
20. ### Construction Steel cage weight load capacity needed

I have a VERTICAL standing square tube 1.25" x 1.25" x 1/16" thick. Length/Height = 79" Material = steel How do you determine its max load capacity for this tube when mounted vertically? I plan to use 18 of these vertical posts, evenly spaced, creating an 83" x 131" rectangular structure. They...
21. ### Finding the weight of an object submerged in water

I have solved the question in the following way: The downward force is equal to the upward force. the upward force is equal to the weight of water displaced. If we find the weight of the water displaced then we will know the upward force. And since upward force is equal to downward force, we...
22. ### Calculating Weight Ratio of PEO and LiClO4 in PEO-LiClO4-Al2O3 PE Samples

So i found this on a journal, and im wondering what is n and how can i calculate the weight percentage ratio between the PEO and LiClO4. Here is the instruction. To prepare PEO-LiClO4-Al2O3 PE samples, predetermined amounts of LiClO4 (such that oxygen to lithium ion ratio is n:1) and Al2O3 (as...
23. J

### Does induced drag theory include the Lift = Weight condition?

This is usual induced drag diagram. I have 2 questions: From Kutta–Joukowski theorem Fr is always perpendicular to effective airflow. 1. Does it mean for case without effective airflow(zero induced downward velocity), Fr is perpendicular to freestream airflow,so drag is zero? When effective...
24. ### I Bicycle front tire wobble due to weight on the back of the bike

I am a bit overwhelmed with your forum site. I was not sure where to post my question...Here goes- Full details…I have an e-bike. It weighs about 55 pounds. I have ridden it for the last year with a canvas bag attached to the rear flat book carrier. The canvas bag measures 19” long, 9” tall and...
25. ### Why doesn't aircraft weight affect descent angle in a gliding flight

It's a homework question, but I feel like it fits better in this forum. The solution fails to convince me because C_D and C_L can be both written in terms of weight: $$C_L=\frac{2W}{\rho v^2 S}$$ $$C_D=C_{D0}+k_1 C_L(W)+K_2 C_L(W)^2$$ Question: Solution: Any insight will be appreciated.
26. J

### I Does Pulse and Glide only work with manual transmissions and a kill switch?

When car drive uphill, gravity/weight has drag component, that is reason why you must add more throttle compare to ligther car at same constant speed uphill. So logicaly car increase fuel consumption. But if you drive downhill, gravity/weight has thrust component, so your top speed("terminal...
27. ### Minimum screw thread engagement to support weight?

Hello All, I know there are rules of thumb and thread engagement calculators online but I am trying to find mathematically what the minimum number of threads acceptable would be. I currently have an eyebolt that will be torqued to a specific value. This eyebolt setup will then need to lift a...
28. ### Forces on a rope when catching a free falling weight

If I am not wrong, F = 2*10*9.81*4/0.2 = 3924N (0.2m considering 5% stretch in 4m long rope)
29. ### How can mass be measured independently of gravity?

Hello The formula Mgh is commonly accepted as the work done by raising a mass by a distance h, where M is defined as the mass of the object raised. However, is this really the mass, or the weight, simply obtained by weighing the object? If it's the weight, then doesn't the equation...
30. ### Apparent weight problem (kinematics + conservation of Energy + Newton's laws)

Hello there, I have tried the problem but don't get a different of 6g's as I am supposed to. I am not sure whether I interpreted the problem in the correct way, but I would love some feedback/hints on what went wrong in my solution, thanks in advance. Solution: SITUATION DRAWINGS + FBDS so...
31. ### I Shock Load on Rope: Weight Limit Analysis

Hello, I’m not sure if the proper term is shock load. If a person is using a device and rope to lower themselves from a high point and they’re descending fast and then suddenly stop does that create a shock load? The device attaches to the rope and when a person squeezes the device it allows...
32. ### I Weight required to hang straight down with known torque

How much Weight (W) is required to keep a weight hanging straight down when the torque is known on a rotating shaft? Please see attached image. Assume a lever weight of zero to keep it simple.
33. ### I Effective weight vs distance to the point of attachment of the weight

Hi, I want to know how to calculate the effective weight if i have an object with the weight 'X' that is mounted from the side to a wall, and what happens with the weight if i increase the distance between the wall and the object. The reason i ask is as follows for the interested. I have a...
34. ### Knowing when to decompose weight vector vs. normal vector

Good afternoon everyone, I have a question on Newton's 2nd Law regarding objects on a generic incline. Take for example, a car on a banked curve: Here in the picture I've provided, you can see that the normal force has been decomposed into the x and y components via sine and cosine of the...
35. ### I Calculating your weight in an elevator

I was watching one of Walter Lewin's lectures, he gave an example of a scale placed at your feet in a moving platform, apparently your weight changes when the moving platform accelerates downward, my question is if my reasoning is correct. I'm wondering why your feet stay in contact with the...
36. ### Home project: Kilogram Force on wheel bearings

Hi all. I'm designing a custom spare wheel carrier for my 4wd and currently seeking knowledge on which bearings to use, so I need to work out what force on the bearings will be when it's open (closed will be locked and fully supported!) The example image is simplified for calculation. Close...
37. ### How Can I Maximize My Learning Potential as a New Scientist?

Hi everyone! New member here, not much smarter than a monkey but willing to learn. Thanks for the opportunity to learn from yas!
38. ### I Apparent Weight problem (falling beam)

Each weight: 2 Kg Hello All, I'm trying to understand an "apparent weight" problem and check my answer. Please use the picture attached. A weightless beam is at first resting over my palm, it has one 2 kg weight on each end of it. It is suspended to the ceiling by a rubber band. I drop it and...
39. ### Will my fish tank stand hold the weight?

Tank volume is 768l plus the tank and rock to go inside 2000m x 640mm wide x 600mm high Stand is made of 35mm square x 3mm wall thickness. Tank width is the same as the steel frame, notice the tank is not over the end legs. Wooden top is 50mm thick pined and glued planks... 4x top supports...
40. ### B What is my apparent weight in water?

Hi, I was wondering, what is my apparent weight in water? For example, when I tiptoe on land, my calf muscles are pretty much lifting all my body weight. But if I were to tiptoe with just my head out of the water, how much weight would my calves be lifting? And as I move to shallower water, how...
41. ### Pulley system to balance the weight of a person

Since we are dealing with an ideal rope, we have that ##T_1=T_2=T_3=F and T_2+T_3=2F=(m+m_p)g\Leftrightarrow F=\frac{m+m_p}{2}g.## ##T_4=3F+(m+m_p+M_p)g=\frac{3}{2}(m+m_p)g+(m+m_p+M_p)g=(\frac{5}{2}m+\frac{5}{2}m_p+M_p)g## and ##T_5=mg-2F.## Is this correct? If not, I woould appreciate a brief...
42. ### B Understanding Weight and Inertia: A Comparison of Mars and Earth

https://www.feynmanlectures.caltech.edu/I_09.html “Weight and inertia are proportional, and on the earth’s surface are often taken to be numerically equal, which causes a certain confusion to the student. On Mars, weights would be different but the amount of force needed to overcome inertia...
43. ### B Can I hold down more than my body weight on a 1 to 1 system?

Can you pull down/hold more weight than your body using your muscles? Imagine a 1 to 1. One side is suspended 190 pounds, the other is me, 175 pounds. Can i, using my muscles and standing on the ground, hold that suspended weight off the ground? I understand if i lock out my arms and...
44. ### I Understanding tension and centripedal force in a puck and weight

For practice I did the following problem: Solving this problem mechanically was simple enough using the following force diagrams: Then $$F_{net_M} = T - Mg = 0$$ Due to the stationary condition $$T = mg$$ and $$F_{net_m} = T = ma_c$$ $$T = ma_c$$ Because centripedal acceleration is...
45. ### VTOL RC Airplane Tricopter COG, Liftoff Weight Calculations

Hello, I am interested in making an RC plane as illustrated. Some questions: 1. Given that the build material of the plane will be 3d printed out of PLA and I want the wingspan to be between 1.2m - 1.35m ideally. How can I calculate the minimum wingspan/wing shape/wing area to carry a payload...
46. ### Engineering Calculating the percent composition of weight of an alloy

I found the density of carbon and iron: ρ_fe=7.87 g/〖cm〗^3 ρ_c=2.26 g/〖cm〗^3 Using equation 2: atom density of iron and carbon N_fe = 8.48e22 cm^-3 N_c = 1.13e23 cm^-3 Using equation 1: macroscopic scatter and absorption cross sections of iron and carbon Σ_a,fe = .217 cm^-1...
47. ### Calculating Lifting Weight for a Horizontal Metal Tube

how do I calculate how much force is needed to lift a horizontal metal tube to a vertical position. The metal tube is 25 feet long, weighs 300lb and and pivots 5 foot from the bottom. I will be using a hand winch and the cable attaches at the bottom of the 5 foot end of the tube.
48. ### MHB Balancing Weight on an 8m Pole: Find the Solution

A man and a boy hold opposite ends of 8m long pole which is horizontal. A mass of 200 kg is tied to the pole. If the man is to support four times as much weight as the boy where along the pole must the weight be tied? Can someone please help
49. ### 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...
50. ### Tongue weight capability of 2x3x.125 steel tube at 21"?

Hello everyone. I'm building myself a half-rack for weight lifting that included 2 overhung support beams above from which to hang a safety strap incase of a failed lift. They are made from 2x3x.125 steel tube (they're Oriented with the 3" vertically). The tube are overhung by 21". How much...