I"m not familiar with the violin, but this is something I’ve been wondering about when watching: the violinists’ bows are all synchonized, so they all do upstrokes and downstrokes at the same time. Is this for the visual æsthetic, or does it matter to the tone? I would have thought that the note would sound the same whether the bow goes up or down on the string - or am I wrong on this?
Musical notation does suggest whether the bow should change directions between two notes, or just keep the bow moving.
I suppose it is a sign of a good orchestra that they all stay synchronized throughout an entire work; I gave up after high school, which was a rotten (but spirited) orchestra, so I don’t really know.
Professional musicians?
I asked a violinist friend once. He said you always start by pulling down unless otherwise specified in the music. Other variations, such as tapping with the bow or plucking, are also specified. There may be minor differences in tone, but a string section is like one big instrument, so it should be synchronized both visually and aurally.
A better violinist than I might contradict me, but I believe individual players “think alike” since that’s the way they have been taught to play. Downbow on initial downbeats, for example. There are music symbols the composer can use if he wants the “natural” motion to be ignored and a specific bow action taken (downbow when the player might naturally upbow, pizz. plucking instead of bowing, etc.)
In the absence of any special marks, each note will be played with a separate, opposite bow. A slur (short or long horizontal curve) indicates multiple notes to be played with a single bow.
A practical thought - musicians in the pit can be packed in pretty tightly. If everyone’s bowing the same direction at the same time, there’s less chance of poking someone.
Your downbow is generally stronger than your upbow, so notes on the beat usually get a downbow. The composer might indicate up- or downbow with special symbols: downbeat is like a square with the lower edge missing; upbeat is like a condensed “V.”
If you’re talking about professional musicians, usually they know what they need to make a particular sound, and sometimes they have to anticipate a particular note by figuring out the bowing so that the preceding note is the opposite stroke.
When all else fails, they follow the concertmaster.
Kevbo played violin frome elementry through high school and knows this one.
Because it looks like ass if they each bow individually.
The first chair of each section will decide upon bowings, and all violinists, violists, cellists, etc mark up thier sheet music accordingly. Occasionally the composer and/or arrainger will provide markingings as well. Mostly this will be to indicate heavilly accented notes are to be played on down strokes. The standardized notation is a squared off U for downward (right arm extending) strokes, and a ^ for up strokes (right arm bending). These are normally written above the lines of music, while dynamics (forte, piano, mezzo forte, creschendos, etc.) are written below.
Bowing in unison takes some practice for beginning orchestras, probably not so much for the pros. Once you are on, it is fairly hard to get off unless you get lost. If you get lost, you look for the upcoming prominate downstroke, and join in at that point.
What the others have said (although Kevbo’s forgotten what the symbols look like 
) It’s 90% about sound, 10% about visual aesthetics.
Uniform use of the bow, which extends far more than getting it in the correct direction, is essential to create a uniform sound from a string section. Bow speed, weight, and particular techniques for particular passages are all elements of this. Being able to match others around you, and specifically those in front of you, is a necessary skill for ensemble playing which string players have to acquire.
On rare occassions, ‘free bowing’ will be used, where there is no attempt to match actions. This is normally in long still passages, where the strings play a quiet static accompaniment.
Can you really hear a difference in tone between upstrokes and downstrokes when blindfolded? It seems to me that the Helmholtz motion would impart mathematically identical forces at the bridge, and I can’t see a means of making the friction characteristics of the bow asymmetric or anything.
It’s no so much the different tone for any one small fraction of a second; rather it’s how the tone changes during the entire bow stroke. A downstroke, because of the mechanics of a violinist’s arm, will change in pressure and angle of the bow during the stroke. An upstroke will change slightly differently.
For instance, there’s a little more control at the beginning of a downstroke; it’s easier to either start a loud note exactly on cue or start very softly and get louder.
Ah, I see - it’s more about control in the different strokes rather than tone per se. Thanks.
Yes, spot on.
It is perfectly possible to keep a consistent and unchangine tone through long sustained bow strokes, irrespective of direction. Fast or rhythmic playing, however, uses the direction of strokes to its advantage. And some techniques, such as spiccato bowing (bouncing bows) work far better in one direction, and/or at one point along the length of the bow.
It’s a matter of differential pressure between the two ends of the bow. The tip of the bow, where you would start an “up-bow” is farthest from the player’s hand. Because of that, it’s very difficult to exert a lot of pressure on the violin string with that end. You can’t play a strongly accented up-bow due to mechanical disadvantage. Up-bows are most often used for pickup notes (the “da” of “da-DUM”) and notes that should sound weaker within a phrase.
Down-bows start at the “frog” end of the bow, right next to the player’s hand, and so they suffer no leverage penalty. Good players know how to mitigate the difference and play evenly across the bow, but if they want to produce a strong accent or downbeat, the down-bow is the easiest way to do it. It produces a stronger sound than an up-bow, and any reasonably good player can usually tell the difference.
So, the general answer to the OP (which has already been said now that I preview) is that having the entire section bow in the same direction makes for a more unified pattern of accented and unaccented notes within a phrase, and a more unified sound in general.
Can I hijack this a bit?
What about left-hand players? Do they bow with their left hand (which sounds dangerous to the guy on their right)?
I can see that it might be advantageous to put all the lefty’s together to keep from poking somebody’s eye out but that’d screw up the sections, wouldn’t it.
I expect, given the explanations above, that down & up are in the same places, though.
Nope. With the exception of a very few folk fiddlers, no leftie plays any differently. There’s no great advantage to having the dominant arm control the bow, because the dexterity required in the left hand is at least equal to that of the right. And both instruments and techniques are asymmetrical: with a normal playing position, the greatest weight can be delivered to the lowest-pitched (i.e. thickest) string, which needs the most power. To have this benefit while playing the opposite way around, the violin would need to be strung the other way…and they’re not designed to work that way. The internal structure, and the thickness of the wood, is different one side from the other.
Very interesting replies - thanks, everyone. I’d not thought of the control and strength issues, but they seem obvious once you point them out.