In the study of physics there are a great number of units representing physical quantities – mass, force, charge, resistance, etc. Most of these units have a base quantity, and a name (usually one that honors a pioneer in the field): volt, tesla, henry, etc. Except acceleration, which is still known only by its constituent units, ms[SUP]-2[/SUP]. Is there any historical reason why there is not a unit of acceleration named after, say, Galileo? It seems like an odd oversight.
From this page.
Sticking with the SI system, there are only seven base units. Of the physical quantities you mention, only mass has a base unit, and of the units you mention (volt, etc.), none are base units.
See Table 1 at this site:
There are a variety of derived units. Some have special names, but many do not. See Tables 2 through 4 at the above link.
Again, within the SI system, not only is there no commonly used “named” derived unit for acceleration, there is also no “named” derived unit for velocity.
Outside the SI system, though, you can express acceleration in terms of g’s, and you can express velocities in knots or even in terms of mach numbers.
Quiet possibly the reason is because it was Newton who first framed the laws of motion with any accuracy - and he gave his name to a unit of force.
Nitpick: Mach number alone tells you absolutely nothing about velocity. It tells you a great deal about the flow configuration (shock angle, pressure ratios, etc.) but without additional information defining the local speed of sound, it is meaningless as a velocity. That’s the whole point.
Now back to your regularly scheduled GQ…
Think about it. There is no famous person’s name used for Position, Speed, Acceleration, the latter two being the first time derivative of the one preceeding it. Acceleration is not special.
Read my earlier post.
In some circles a meter/second^2 is known as a jerk. Sure, it started off as a joke, but it caught on since “jerk” is easier to say than “meters-per-second-squared.”
Not sure which jerk it is named after.
However, the dork unit of angular acceleration (torque/kg = dork) is attributed to Gustav Dork of Vienna (1849-1912). However, for obvious reasons it is not used by most English speaking physicists and engineers.
According to the site listed above, this unit, the galileo, is defined to be equal to 0.01 m/s[sup]2[/sup].
FWIW, I suspect that this unit is only used in a fairly specialized field where small variations in the acceleration due to gravity are significant. Simply by the fact that it is defined as 0.01 m/s[sup]2[/sup] (as opposed to being equivalent to m/s[sup]2[/sup]) makes me think that it is not a derived SI unit (though it is of course metric-based). Also, I’ve never heard of it.
micco, your point on mach numbers is well taken.
Are you sure about this, TGWATY? I’ve always understood that jerk is a physical quantity equal to the first time derivative of acceleration, with units of m/s[sup]3[/sup]. It tells you how fast acceleration is changing with respect to time.
According to the latter website, jerk is referred to as “jolt” in the UK.
Never heard of either of those.
Technically, the jerk is the derivative of acceleration with respect to time. It’s probably not a good idea to call the unit of acceleration the same thing - too much possibility of confusion.
Dang! FriendRob, I thought I was making that stuff up for a whoosh :D, but now you’ve refreshed my memory. I must have absorbed that stuff about jerks subconsciously many, many years ago.
And it’s very little known, but the name for the SI unit of momentum is the Kirk: 1 Kirk is equal to 1 kg m/s. Or so said my department’s Dr. Kirkpatrick, when he discovered that there wasn’t any other name for it.
Hey Chronos, was your Dr. Kirkpatrick by any off chance Ted Kirkpatrick?
As a science teacher, I would also add that using “m/s” for velocity and “m/s^2” for acceleration are more useful for learning about these concepts. If we gave them each a name, it would make the relationship between them less clear. I use units often to show my students how to check their answers. “Newtons” is convenient to say when speaking of forces, but “kg * m/s^2” is more helpful when learning about forces and their relationship to other quantities.