JBRIII

Actually I don't so. I believe there was walkway build over a river in Europe (England?), not that long ago that had to be reinforced for the same reason. The bridge in Washington state came down in the early 50's? ( not way back to me) due to 40 mph winds, bridge surface twisted like taffy unitl it disintegrated.

Longshadow Loc: Audubon, PA, United States

But the bridge in Washington wasn't being marched.

((What about earthquakes?))

Or we can stick to marching.

Had to start with troops marching over some bridge somewhere.
Yea, define "a long tome ago" in number of years.

JBRIII

Correct but same effect, resonance that slowly adds energy. The one in Europe was a people issue I believe, maybe 10-15 ago at most.

wrangler5 Loc: Missouri

Check out the Millenium Bridge in London, opened in 2000. It had serious problems from pedestrian footfalls, although they were not "marching" in step.

https://www.sciencedaily.com/releases/2005/11/051103080801.htm

Longshadow Loc: Audubon, PA, United States

So could loudspeakers............

Any other ways to hit resonance?

(But the object wasn't to see how many ways one can hit the resonant frequency of a bridge,
but discussing troops marching...)

Canisdirus

Longshadow Loc: Audubon, PA, United States

Longshadow Loc: Audubon, PA, United States

BTW - The wind (sideways) compared to marching (vertically), TOTALLY different force vectors in play.

Wyantry Loc: SW Colorado

There is a definite difference between “rusting” and “corrosion”.
Almost all metals will react with oxygen or other elements to change shape or finish; this is corrosion.
Metals or alloys containing iron combine as FeO, Fe2O3, or Fe3O4: this is rusting.
[Common practice (in chemistry, engineering, alloying and similar aspects of “the trade”), regard “RUST” as being exclusively restricted to Iron and its oxides]. There may be an alteration of a metals surface finish, AKA tarnishing.

A list of non-reactive metals: “. . . the Noble Metals are metals that are resistant to Corrosion and Oxidation in moist air (unlike most Base Metals). The short list of chemically noble metals (those elements upon which almost all chemists agree) comprises Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Silver (Ag), Osmium (Os), Iridium (Ir), Platinum (Pt), and Gold (Au).

More inclusive lists include one or more of Mercury (Hg), Rhenium (Re) and Copper (Cu) as noble metals. On the other hand, Titanium (Ti), Niobium (Nb), and Tantalum (Ta) are not included as noble metals although they are very resistant to corrosion.” —Quora answer by Mr. Roy.

As far as pure (or slightly alloyed metals) go, Tungsten, Nickel, Titanium, Zirconium and Aluminum would be added. Aluminum, Titanium, zirconium (and some others) are interesting because of the oxide-layer (Al2O3, in the case of Aluminum) formed, this is the same as corundum i.e. ruby, sapphire; hard, tough, nonreactive.
Iron and steel alloys with sufficient quantities (%) of Chromium (10 to 30%) are rust resistant.
Silver does oxidize, at least on the surface. Large quantities of silver coins have been retrieved that have had enough of the parent metal oxidized that it has become one large black lump. The same with metallic copper.

An example of the current properties of the elements of group 10 are at: https://en.m.wikipedia.org/wiki/Group_10_element.

Data for group 11 are at:
https://en.m.wikipedia.org/wiki/Group_11_element
A similar analysis is available for other groups.
[NOTE: the latest IUPAC nomenclature has done away with the older group 8A or group 8B titling, making the look-up of information a bit confusing.]

In an historical perspective [geologically], prior to a lot of life-on-earth, the environment was Reducing, i.e. without oxygen. Rainfall, runoff, and erosion had transported very large quantities of iron and other metal —in reduced form— into the worlds oceans, which were essentially an iron and sulfur (and other elements) rich “soup”.
When algae, bryozoans, and other oxygen-producing lifeforms began producing Oxygen as a waste-product from photosynthesis, the oxygen content increased to levels that caused a reaction with iron and precipitated vast quantities of iron in Banded Iron Formations, that are found worldwide. In essence, “the world rusted”.

pumakat

It is the copper in sterling and lower purity silver that reacts to oxygen. Fine silver is very soft but does not tarnish.

Longshadow Loc: Audubon, PA, United States

I know, I know...... Rusting is corrosion, but corrosion is not necessarily rusting.
Rusting is iron, everything else is corrosion.
SEMANTICS, PERCEPTION, INTERPRETATION, OPINION, ...... BRASS TACKS

STRUCK A CHORD DID I????

JBRIII

I disagree, the source of the force is different, footsteps versus wind, but the basic mechanism is not, you hit the right frequency so energy keeps feeding in and building. Break the cadence and the same soldiers taking the same # of steps cancel out each other. Mechanism also applies to pushing a child in a swing or the person doing it themselves.

Longshadow Loc: Audubon, PA, United States

Okay, we disagree.

JBRIII

Agree, also if one wants to really get picky, metals like Aluminium, the pure clean metal, corrodes very quicky. What we see is the metal coated with Al203, the stuff of sapphires. This is clear, hard, water resistant and protects the Al. I believe there are iron alloys designed to form a coating which does not flake off and alloy further rusting.
The enviroment also make a big difference. Al dissolves very quickly in alkali. The small metal slivers in Drano are Al, form hydrogen for bubble effect. Take any Al and add to solution of sodium hydroxide = hydrogen gas production plus lots of heat, boiling, splattering, etc. (extreme caution needed).
Al is actually much more chemically active than iron, i.e., thermite, Al + Fe2O3 = molten iron.

alberio Loc: Casa Grande AZ

It works for me.