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26 votes

Why does "potential energy" have the word "potential" in it?

Because it has the potential to produce mechanical work.
NMech's user avatar
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24 votes
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How do suction cups work?

TL;DR: Its not the air that's enclosed inside that creates the force, but the lack of air - or more precisely pressure. First of all some nomenclature (this is for the closed type, there is also the ...
NMech's user avatar
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19 votes
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Why does "potential energy" have the word "potential" in it?

potential (adj.) Capable of being but not yet in existence; latent or undeveloped. The block is stationary and therefore not performing work. If the block never moves, the potential energy remains ...
fred_dot_u's user avatar
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17 votes
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Would a centrifugal flyweight governor system slow down the descent of an object that is free falling down to the Earth's surface? (Revised design)

Once the cylinder is released and starts to accelerate downward, the rotating flyweights should pivot upwards to a certain degree (as shown in the drawing) and should act as a drag on each of the ...
jpa's user avatar
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14 votes
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Is radians a dimensionless quantity?

radian is a derived unit, defined as the ratio of arc length to radius. As the ratio of two lengths it is dimensionless.
agentp's user avatar
  • 949
12 votes

Do outer fillets|chamfers also reduce stress as inner ones do?

Sorry for not taking your "Thin Hollow Brick-Shaped Object" as an example - I felt a standard notched test specimen would illustrate the principle more clearly: It can be seen that adding external ...
Jonathan R Swift's user avatar
11 votes
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What is the difference between the Polar Moment of Inertia, $ I_P $ and the torsional constant, $ J_T $ of a cross section?

The torsion constant $J_T$ relates the angle of twist to applied torque via the equation: $$ \phi = \frac{TL}{J_T G} $$ where $T$ is the applied torque, $L$ is the length of the member, $G$ is ...
atom44's user avatar
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10 votes

Calculation of Clamping force from bolt torque

That figure is about right for a low tensile bolt. See also this calculator and this table As a reality check if we approximate to a cross sectional area of 7 mm2 and a load of 1000 N that gives a ...
Chris Johns's user avatar
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9 votes
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"u" vs "n" orientation of channel profiles: why difference in strength?

You are correct. A channel section in a "u" or "n" orientation is obviously asymmetric around its transversal x-axis. This means that its centroid is not located at the midpoint of its height. ...
Wasabi's user avatar
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9 votes
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Why are spur gear ratios not always whole numbers in practice?

Gear ratios can be referred to as hunting and non-hunting ratios. In a non-hunting ratio, any one gear tooth will contact its corresponding gears' teeth in the same place every time. In a hunting ...
Todd's user avatar
  • 116
9 votes

What is Saint Venant Principle?

The intuitive meaning of Saint Venant's principle is that "if two different sets of applied loads are statically equivalent, then the differences between the two stress patterns they create are only ...
alephzero's user avatar
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8 votes
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Contradictory units for moments of inertia

I spent some time searching on this one, and surprise surprise, Imperial units strike again! The good old "pounds-force pounds-mass issue" masked with ounces. This is why any calculation ...
ericnutsch's user avatar
  • 8,176
8 votes

What is Saint Venant Principle?

To add to @alephzero's answer, here's an layman's explanation of Saint-Venant's Principle: far enough away from the load's point of application, equivalent loads can be treated as identical. For ...
Wasabi's user avatar
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7 votes
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Force Balance Question

The problem here is that $dr$ is not the radius, $r$ is! Your expression for the infinitesimal area should be $2\pi r dr$: this is for a thin loop of radius $r$. (Excuse the crude diagram): So $r$ is ...
Involute's user avatar
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6 votes
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How to Calculate the Minimum Radius a Rod Can Can Be Bent Staying in the Elastic Range?

If we're staying within the realms of beam theory, we can go with this approach which is valid for any material that exhibits linear-elastic behaviour before yield: The curvature of a beam is related ...
Robbie van Leeuwen's user avatar
6 votes

Why is the Stress vs strain diagram preferable to the Load vs displacement diagram?

The Load-Displacement (or Load Extension) and stress strain diagrams are two diagrams identical in shape. See below. The main visible difference is the values on axis (which are at first glance ...
NMech's user avatar
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6 votes

Why does "potential energy" have the word "potential" in it?

In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, attachments, electrical charge, magnetic field, mass, etc., and ...
sasguy's user avatar
  • 71
5 votes

Adding a lubricant to an already lubricious material, how is CoF affected?

You can't calculate friction coefficients this way. At the atomic-scale level, the friction coefficient depends on the interactions of the two materials across the interface. If you measure the ...
alephzero's user avatar
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5 votes

What is the difference between tolerance and uncertainty in measurement?

Tolerance is a property of a design. Tolerance is a acceptable deviation from plan that is designed as part of your acceptance criteria. You document this in your drawing/contract either as a general ...
joojaa's user avatar
  • 3,577
5 votes

Glass panel engineering at work

Glass tends to contain quite a lot of residual stresses from the manufacturing process and these will tend to be concentrated near corners (depending on how the sheet was manufactured). There is also ...
Chris Johns's user avatar
  • 15.2k
5 votes

Force required to rotate an object on a plane - moment of inertia?

Since the friction is not known, the torque to overcome that friction can't be known either. You therefore can't do what you want since the problem is under-constrained.
Olin Lathrop's user avatar
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5 votes
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Failure in torsion

As a rule of thumb: When brittle materials are subjected to torsion they fail in the plane, where tension is at its highest, i.e. at a 45° angle. Ductile materials on the other hand fail in the plane ...
Andrew's user avatar
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5 votes
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Are the points of inflection and contraflexure the same?

A point of inflection is defined as the point where a function changes from convex to concave or vice versa. For a function $f(x)$, this is frequently mathematically defined as the point where $f''(x)...
Wasabi's user avatar
  • 13.1k
5 votes

Would a centrifugal flyweight governor system slow down the descent of an object that is free falling down to the Earth's surface? (Revised design)

jpa made a good answer on why the weights wouldn't flex upwards. I'll add another point. Newton's third law says that for every action, there is an equal and opposite reaction. For the box to be ...
BillThePlatypus's user avatar
4 votes

Isotropic materials and levels of stress

In general the answer is yes, however for particular cases the stresses could be the same. Your stress "definition" (stress = load/area) is valid for uni-axial stress state, for example a rod ...
rozsasarpi's user avatar
4 votes

How to design a gear escapement like in an old pendulum clock?

The mechanism is called an "escapement", and part of its function is that the gear imparts energy to the swinging teeth in order to keep the pendulum (or whatever) moving in spite of any frictional ...
Dave Tweed's user avatar
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4 votes
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Finding downward force of lever bar

The input force is 18.5+20.5 ft away from the fulcrum and the load is 18.5 away from the fulcrum. This means the force applied to the load is $\frac{(18.5+20.5)}{18.5} = 2.1$ times greater than the ...
ratchet freak's user avatar
4 votes

How I can compute cutting processes with continuum mechanics?

Real-world engineering example To my knowledge there are no simple analytical methods of determining whether an object such as a sword can cut cleanly through any arbitrary object. In manufacturing ...
ConjuringFrictionForces's user avatar
4 votes
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polar moment of inertia for compound shape

Without looking up all the formula's for you, the approach to this problem is rather simple. Find the polar moment of a solid cylinder, and subtract off the polar moment of the holes. For the off ...
agentp's user avatar
  • 949
4 votes

Thin walled pressure vessel

Both Axial stress, (parallel to the axis of cylindrical symmetry) and Hoop Stress (in the tangential direction) are "Normal Stresses". They are "Normal", because, if you consider an infinitesimal ...
Jonathan R Swift's user avatar

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