# Tagged Questions

Analysis of a system of bodies where all forces are in balance and there is no motion relative to a chosen reference frame.

4k views

### Statics: particle mechanics versus rigid body mechanics

In particle mechanics where the notion of rotation does not apply, particles are said to be in static equilibrium when the sum of the external forces acting on the particle of interest in all ...
46 views

### Tension on wire holding open door, using moments about a hinge? [closed]

Using moments about the hinge, what is the tension in the wire holding the door open? The wire is horizontal. The door is 5m. See diagram: The door is at tan inv (3/4) : 36.9 deg to the ...
26 views

### When an object hangs from a Rigid rod is the force of the weight located in the center of the sign?

From the rope that supports the sign (assuming the mass is distributed evenly). If the length of the sign is, $L$ can I model it so that the weight is concentrated at $\frac{L}{2}$ Therefore, the ...
117 views

### how does one divide stress in such a bridge? [closed]

I want to build a spaghetti bridge like this: I have two spaghetti types: T-type (designed to tolerate tension) and C-type (designed to tolerate compression). A mass $m$ is hanging from the point ...
42 views

### Applied forces on a bridge [closed]

What are the forces that acted on the 6 types of bridges? Beam, Truss, Cantilever, Arch, Suspension, and Cable-Stay? What formulas do you use to get the forces? I'm curious since there is nothing ...
53 views

### Difference of water pressure

We know that $P = \rho gh$, so is it true that water pressure at 2nd floor will be higher than water pressure at 9th floor of a 12 story building?
80 views

### Equilibrium equations

You have one horizontal beam. Its left point is attached to a free pivot at the vertical wall. Its right point is suspended by a rope from the ceiling. Nothing is moved. So $\sum F=0$ and $\sum M=0$. ...
136 views

### Confusion about two-force members

This is my first question here so I hope I get warmly welcomed by answers that would resolve this perplexion :-) This is a statics problem from Hibbeler's Mechanics for Engineers: Statics (13th ...
7k views

### Are circles stronger than triangles?

I've often herd in engineering that "there is no shape stronger than a triangle". I also recall that arches are very strong shapes as well, which can be crudely described as a perpendicularly-...
23 views

### Transferable force

If I for example have two rectangular pieces of steel that are both W=40mm, L=1000mm, H= 40mm and are both completely ridged. One piece of steel is resting on top of the other piece of steel, if I ...
50 views

### I'm building a bubble pane. What can I do to reduce static pressure? [closed]

I'm building a bubble pane, just for decoration in my home, using some patio door glass panes and an aquarium air pump. Soon into my testing, I learned what static pressure is. When I fill it up, even ...
1k views

### How does centre of gravity influence the equilibrium?

Ok! This really makes hard to think, how does a single point determine the object's equilibrium? If an object is displaced from its equilibrium-position & if the equilibrium is stable, the object ...
28 views

### Distortion of non-circular cross sections upon torsion

True or false? Non-circular cross sections can be non-planar when torsion is applied. This was on a quiz today and I wasn't sure of the answer. I guessed true by intuition, but does anyone have a ...
65 views

### push up weight distribution [closed]

I'm about 84 Kg, in push up position (hands on the scales) the scales show about 54 Kg. Can anyone explain briefly the physics of the weight distribution? (I did high school physics decades ago - can'...
81 views

### What is the easiest way to experimentally determine the center of mass of an irregular 3d object that has a non-uniform density?

I want a method that can be done in a basic high-school lab.
416 views

### How is normal force distributed along the surface of contact?

Help me settle this argument. A mass $m$ is placed on a thin diving board. The base of the diving board has mass $M>>m$. Does the board tip over? I drew the following FBD and concluded there ...
117 views

### A question on Rolly polly dolls

I was reading on rolly-polly dolls when the following questions crept into my mind How exactly does center of gravity play a role which helps rolly-polly doll to stand up on its own? Can a rolly-...
75 views

### Lever Mechanical Advantage

In the attached image the force output of the plank is calculated to be the work done (FDf) divided by the height the block rises (Dw). So the force the plank applies on the block is (FDf)/(Dw). But ...
1k views

### Weighing with One-Foot Scale

I stand with left foot on a scale and the other on a piece of effectively incompressible material at the same initial height at the scale's top surface. The weight shown is WL. I repeat with right ...
37 views

### Why can't we have more than 3 moment equations in equilibrium equations

Excuse me for a kind of stupid question but, In statics of a 3D rigid body, the equations to determine equilibrium are at most 6 (Fx Fy Fz Mx My Mz = 0) (not counting those from hinges and rollers). ...
83 views

### Planks, supports, and a scale [closed]

I've got two equal dimension planks with the same homogenous mass. They're placed next to each other like this (bird's eye view): [ ][ ] They're sitting ...
681 views

### How to calculate Young's modulus from a set of data?

The set of data are force vs deflection. Is Young's modulus constant for a material? If the beam is fixed by one fixed support and one vertical support $E = \frac {F}{δ}\frac{3.5L^3}{384I}$
142 views

### Why is it effectively impossible to balance this rectangle block on a triangle block? (See photo)

I've always wondered why it's basically impossible to balance a rectangle block on top of a triangle one like this. This is my nine-year-old giving it a try. I have never in my life gotten it to ...
11k views

### Calculation of the maximum load to the bar

Looking for a way of calculating the maximum weight (W) to the rod with the given length (L) where the rod did not break and that only bend for (b) mm. Need only approximative solution (read: ...
258 views

### Can structural trusses in centrifuges be helpful at all?

Imagine a rotating space station for the purpose of creating artificial gravity. Generally, such a space station is portrayed as a ring or a cylinder. Images of these space stations often have lines ...
182 views

### How exactly do walking canes and crutches help?

I am reading introductory physics, and there is a chapter on equilibrium. In the chapter, the author mentions how devices can exploit distribution of forces to help those that are physically ill, via ...
66 views

### Tension along a curved surface [closed]

I'm curious what the tension in a rope will be when its exposed to a uniform load. Assuming a similar setup to this question what will the tension along the rope/tube be?
30 views

### Shear flow in J section type beam

What does the distribution of shear flow look like in a J section type beam. I'm only interested in a qualitative picture of it. I'm not interested in the calculations themselves. It is the top of the ...
272 views

### Simple Beam Worst Case Scenario

Part 1 If I have a simple beam with two supports and a static load, does placing the load in the center push the beam closest to breaking (catastrophic failure)? Will this be more likely to break ...
212 views

### How to design a stable table?

Imagine a round table, standing on one central leg. The central leg has a base for balance. That base is what I am referring to. What physics do I need to understand to design a stable table? For ...
2k views

### How to calculate the supporting force exerted by a stationary object (cupboard) and support (brackets) for it?

I have a wall mounted Stuva Ikea cupboard, which measures 60x64x30cm. The base is 64x30cm. It is already supported by 2 holes at the back base, (64x60cm). But I need to add in L shape brackets ...
2k views

### Two people are holding either end of a couch, is one person exerting more force than the other?

I was carrying a couch with my flatmate yesterday, and I started thinking about this. Often when carrying objects like this, one person will be taller and has thus lifted his end of the couch higher ...
237 views

### Connection between moment/torque and centre of gravity?

So I understand how moments work with regards to basic examples like pushing a door, in that the further you are away from the hinges of the door, the greater the moment, which is like a turning force....
58 views

### Distribution forces

I've got two trees and between them is a rope. When someone about 100kg sits at the center of the rope, what are the forces on both parts of rope (to the left-hand side from the person and right-hand ...
41 views

### Half of a uniform disc suspended by two strings [closed]

Suppose we have a half of a thin, homogenous disc hanging from the ceiling as shown: Given the weight of the disc $Q$, calculate tensions in strings $S_1$,$S_2$. Now this seemed like quite a simple ...
113 views

### Formula for balance with three arms?

I'm searching for a way to express the angle of the arm of a balance instrument expressed in the weight that is present in one arm. For a two legged balance one could use the moment formula: moment = ...
127 views

### Determining the components of the force on a curved surface due to pressure

I have a cross section of a half-tube with a pressure gradient across it causing a force outwards. I am attempting to extract the vertical component (in relation to diagram) of the force on this semi-...
12k views

### Why can't a rope be pulled completely straight?

I have found several discussions on how to calculate the sag of rope that is tied off at two points (like a tightrope), and I understand it to a certain extent. What I can't wrap my head around is how ...
55 views

### How to find the spring coefficient of a simply supported beam?

So I've been searching wikipedia and google but nothing can show how to find the spring coefficient of a simply supported beam with a uniformly distributed load. The spring coefficient, $k$, is ...
203 views

### Floating objects and fluid statics

If an object is floating, I know about how buoyancy force (density of liquid* volume displaced* g) must equal gravitational force (density of object* volume of object* g). Can someone explain if it is ...
2k views

### Calculating torque in 3D?

Say you have a sphere, and you have several torque vectors acting on it, all at different points. Say you have the vector (6i + 3j + 5k) originating from point A, and the vector (3i + 1j + 9k) ...
590 views

### How to calculate the normal force exerted by a fulcrum off-center?

So I know that $F_N$ exerted by a fulcrum right under the centre of mass for, say, a long horizontal rod, is equal to $mg$. But what if the fulcrum is off the centre of mass either to the right or the ...
155 views

### How many bricks can be put without disordering the equilibrium? [closed]

A homogenous brick with length L, is on a horizontal surface. On this brick are put one after another other bricks, which are the same with the first. Every brick is moved along L/5 units horizontally ...