a buck is a buck is a buck

Q: How many dimes would you need to equal the weight of 4 quarters?

MisterBixby said, "Wouldn't it be swell if the answer were 10?"

Yes it is.

It seems everyone got the numerical answer to yesterday's "pop quiz" correct. As iceberg points out, one dollar's worth of dimes and one dollar's worth of quarters both weigh exactly 22.68 grams. Mr. Carson did his research on Wikipedia. I did mine at usmint.gov.

I'm very curious about Joe's guess ("so that vending machines or parking meters can judge when you've put $1 in"). I doubt very much it's the main reason, but I'd like to look into how vending machines work and whether they were already prevalent in the age of silver coins. My own sense of the main reason for consistent coin weight is implicit in my answer to the question "Why do dimes and quarters still have milled edges?"

I also suspect that the inconsistent weight of new dollars (the Susan B. Anthony Dollar and the Sacagawea "Golden Dollar") has played a significant role in their failure as money.

Like the dime and the quarter, the Kennedy half-dollar is "reeded" (has milled edges) and has the same metallic distribution: "8.33% Nickel, Balance Copper". It weighs 11.34 grams, so 2 half-dollars weigh the same amount as 4 quarters or 10 dimes.

Here's what the FAQ on the website of the United States Mint has to say about coin size:

Why is the one-cent coin (the penny) larger than the ten-cent coin (the dime)? What determines the sizes of our coins?

The sizes of United States coins can help you to identify each one, but have nothing to do with their value. [emphasis added throughout by bk] The first U.S. five-cent coins (nickels) were made of silver, and were smaller than the ten-cent coins (dimes) in circulation today. You may be interested to know that our coinage system, to a certain extent, has grown out of custom or, in other words, out of daily use. When United States coins were first produced in 1793, our standard coin was the silver dollar. The United States Mint produced the rest of our coins (except the one-cent coin) in a proportionate metallic content to the dollar, with the sizes regulated accordingly. The half-dime (or five-cent denomination) had 1/20th the amount of silver contained in the dollar. Our 10-cent coin contained 1/10th the amount of silver, the quarter-dollar coin (the quarter) contained 1/4th the amount, and the half-dollar coin contained 1/2 the amount. Mint officials recognized the need for a larger five-cent coin because the half-dime was exactly half the size of the dime. This proved to be too small for convenient handling by the public. Adoption of the five-cent coin as we know it today occurred in 1866. The Mint increased the coin's size and changed its metallic content from silver and copper to a combination of copper and nickel.

Notice how they imply that the silver content of US minted coins was somehow a decision of the US mint, rather than a requirement for the coins to be treated as money. Notice how they label this requirement "custom". Notice how they call "The first U.S. five-cent coins" nickels. Why would a 5-cent coin have been called a "nickel" before it was made out of nickel? Isn't it more likely that the people themselves later called the new smooth-edged 5-cent token a nickel to distinguish it from the real silver coin it replaced?

You can find silver half-dimes on ebay.

This is how small they are: