# Questions tagged [statics]

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

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### Why is the shape of a hanging chain not a “V”?

From Wikipedia: To answer this question: "What is the shape of a chain suspended at both ends?" we can use the variational principle that the shape must minimize the gravitational potential energy. ...
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### Hanging a hammer from a table and a stick so that its midpoint is outside of the support of the table

I came across this pic on the internet today. At beginning I thought it is just not possible because the centre of mass is way off so gravity will generate torque making the stick and hammer fall. ...
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### Why won't a tight cable ever be fully straight? [duplicate]

I posted this picture of someone on a zipline on Facebook. One of my friends saw it and asked this question, so he could try to calculate the speed at which someone on the zipline would be going when ...
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### Why are arched bridges stronger than flat bridges?

To keep the question brief: in bridge design, why is the arch structure favoured compared to a simple flat one? In other words, how does the curved platform alter the force decomposition of the load ...
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### Why does the weighing balance restore when tilted and released

I'm talking about a Weighing Balance shown in the figure: Press & Hold on onside of the horizontal beam and then release it. It makes some oscillations and comes back to equilibrium like shown in ...
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### What holds up the lowest point of a rope following a catenary curve?

A catenary curve is the curve followed by a rope suspended at both ends in uniform gravity. I thought I would try to solve it myself because it seemed like a good challenge, but almost immediately I ...
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### 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 ...
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### Hydrostatic friction: why do water droplets stay at rest on an inclined glass surface?

This is a non-expert question on a (seemingly simple) text-book topic. The question is about "hydrostatic friction", defined as follows. Consider a drop of water resting on a flat surface. ...
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### What is the role of pillars in bridges?

As I can see in the picture, there are so many pillars which are holding the bridge. This picture gave a question to me that what are these pillars doing below the bridge?? An appripriate answer ...
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### 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 ...
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### Where does the extra equation come from to determine the forces from an object on a table?

I have a question about basic statics but somehow I cannot manage to find the answer on my own (btw, this is not a homework. It's been so many years since school for me...). The problem is very ...
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### Moment of Inertia, why $r^2$and not $r$?

So my engineering mechanics book includes a brief discussion on area moments of inertia. Unfortunately, the ensuing chapter is predominately computational in nature. I don't have a thorough grasp of ...
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### What is the force on the arms in a pushup?

What force do the arms have to generate to do a pushup? Let us look a this simplified model: The body can be represented by the green plank of mass B. Its angle to the ground is $\theta$. This ...
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### Newton's Third Law As Discussed in Den Hartog's Mechanics

A question, but some preliminaries in order to avoid answers involving concepts not yet introduced in the text I'm reading--Den Hartog's Mechanics. Near the very beginning of his book, Den Hartog ...
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### If 1 screw can support 120 lbs, how much weight can 25 screws support?

While this is about a home improvement project, I figure the core part is interesting physics. My situation is this: I am hanging 500 lbs of drywall (two layers weighing about 250 lbs each) on 5 ...
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### Beam attached to a wall

Suppose I have a rigid beam attached to a wall, how can the reaction force on the point the beam is attached to generate a static equilibrium on the beam? ...
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### How does torque work?

Why can we assume the the net torque is equal to zero when we pick one of the points as the axis of rotation. For example if we selected the left leg of the table for the axis of rotation why can we ...