26
votes
Why does "potential energy" have the word "potential" in it?
Because it has the potential to produce mechanical work.
- 24.3k
25
votes
Accepted
From an engineering standpoint, what is the purpose of the indent in a coffee lid?
From the "Solo Traveler" patent:
A more specific object of the present invention is to provide a lid having an opening formed therethrough to enable drinking, and having a recess formed in the lid ...
- 743
24
votes
Accepted
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 ...
- 24.3k
19
votes
Accepted
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 ...
- 6,940
17
votes
Accepted
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 ...
- 1,943
15
votes
Accepted
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.
- 959
13
votes
Accepted
Calculating torque needed to climb a graded hill
I think you're overcomplicating things. To push 85 kg up a 15% slope against gravity of 9.8 m/s2 requires a force of
$$ \sin (\arctan (0.15) ) = 0.1483 \approx 0.15 $$
$$F = 85 kg \cdot 9.8 \frac{m}...
- 6,874
12
votes
Do outer fillets|chamfers also reduce stress as inner ones do?
Sorry for not taking your "Thin Hollow Brick-Shaped Object" as an example - I felt a standard notched test specimen would illustrate the principle more clearly:
It can be seen that adding external ...
- 7,726
10
votes
Why do we neglect the radial stress in case of a thin pressure vessel?
I've been doing large pressure vessel design for a while, and ultimately it comes down to what is negligible v. what is not. Especially in the realm of atmospheric storage vessels, scrubbers, or ...
- 5,343
10
votes
Accepted
What is the difference between the Polar Moment of Inertia, $ I_P $ and the torsional constant, $ J_T $ of a cross section?
The torsion constant $J_T$ relates the angle of twist to applied torque via the equation:
$$ \phi = \frac{TL}{J_T G} $$
where $T$ is the applied torque, $L$ is the length of the member, $G$ is ...
- 2,631
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 ...
- 15.2k
9
votes
Accepted
"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. ...
- 13.1k
9
votes
Accepted
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 ...
- 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 ...
- 12.5k
8
votes
Accepted
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 ...
- 7,904
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 ...
- 13.1k
7
votes
Accepted
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 ...
- 1,317
7
votes
Accepted
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 ...
7
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 ...
- 24.3k
6
votes
Accepted
What is the relationship between drive shaft diameter and torque output?
No. Your basic problem is that "torque is proportional to radius" is wrong. Torque is the expression of normalized rotational force independent of radius.
For example if a motor can deliver 10 Nm ...
- 11.4k
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 ...
- 61
5
votes
Accepted
What is micro-electromechanical systems (MEMS)?
One way to think of MEMS is regular mechanical systems, but at a very small scale. Often these tiny systems are fabricated using technology developed for making silicon electronic chips, like ...
- 11.4k
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 ...
- 12.5k
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 ...
- 3,597
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 ...
- 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.
- 11.4k
5
votes
Accepted
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 ...
- 1,166
5
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 ...
- 7,726
5
votes
Accepted
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)...
- 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 ...
- 151
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