26 votes

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

Because it has the potential to produce mechanical work.
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  • 22.6k
25 votes
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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 ...
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  • 743
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 ...
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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 ...
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  • 6,192
17 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.
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  • 979
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 ...
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  • 1,835
12 votes

Practical setup to measure angular velocity

Probably the easiest practical method to measure the frequency of a spinning top with everyday equipment is to analyze the sound created by the motion and look for the characteristic frequency. This ...
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  • 221
12 votes
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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}...
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  • 6,749
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 ...
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10 votes
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Why are tremors of an earthquake felt more on upper floors?

First, your statement is not universally true. Motion of the bottom of a building can be greater or lesser in upper floors. It depends on the type of motion, how free the building is to move in ...
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  • 11.2k
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 ...
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10 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 ...
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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 ...
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9 votes

Final speed of a truck on a slope?

This is a constant acceleration problem on an inclined plane which ignores friction. The force acting on the truck is the force of gravity. The acceleration the truck will experience will be solely ...
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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. ...
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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 ...
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  • 12.5k
8 votes

Is it possible to design a bus that doesn't rock?

You could have active suspensions, which could keep the vehicle level or even roll it into the corner (see for example this PhD thesis), but they are typically prohibitively expensive and not feasible ...
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  • 1,806
8 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 ...
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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 ...
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  • 7,469
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 ...
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7 votes
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Practical setup to measure angular velocity

There are several ways. The most direct is to paint half of the top white and the other black, then point something with a light sensor at it. AC amplify the output a little, then determine the ...
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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 ...
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  • 1,272
7 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 ...
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6 votes

Why are tremors of an earthquake felt more on upper floors?

Harmonic coupling with the building's natural vibration frequencies, dissipation of energy in a massive building, and the variety of vibration modes that can experience coupling could result in more ...
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6 votes
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How can I improve traction on a wheeled vehicle yet reduce friction?

You need to control how fast you apply the power. Some sort of damper mechanism that would allow power to be gradually applied and not cause it to spin out. You could try and wrap the 'power string' ...
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  • 486
6 votes

Mounting and Coupling an Encoder

That model of encoder is not intended for mechanical measurements. It's meant to be used as a fancy knob with high friction, for turning by hand, say, to pick a position from menu on a display, and ...
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  • 6,123
6 votes

Final speed of a truck on a slope?

Fred's answer solves this problem using classical mechanics/kinematics. However, you can also solve this type of problem using an energy approach (which I have always found easier to do - Newton's ...
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6 votes
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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 ...
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  • 11.2k
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 ...
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  • 22.6k
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 ...
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