Where does the figure for a proton's rest mass come from?

[recniabsal]

TL;DR

The proton rest mass value calculation of

The proton rest mass value calculation of 1.672,621,71?, times 10 inverse 27 kg, where does the figure originate from? What kind of figure is it?

 

[DaveC426913]

1.672,621,71x 10^-27 is not a calculation; it is just a (very small) number.

1.672,621,71x 10^-27kg is the mass of a proton.

Do you mean how did we determine how much a proton masses? Did you try Googling that to see where it leads you?

Hint: Read up a little on "Penning Trap".

 

[recniabsal]

1.672,621,71x 10^-27 is not a calculation; it is just a (very small) number.

1.672,621,71x 10^-27kg is the mass of a proton.

Do you mean how did we determine how much a proton masses? Did you try Googling that to see where it leads you?

Hint: Read up a little on "Penning Trap".

It is a calculation. See that multiplication symbol in-between?

 

[phinds]

It is a calculation. See that multiplication symbol in-between?

No, it's a NUMBER. Are you not familiar with exponential notation? Without units it is, as Dave said, just a number. When you add the units, it the mass of a proton, which is an experimental result, not something derived from something else.

 

[DaveC426913]

It is a calculation. See that multiplication symbol in-between?

It is a notation. Specifically, scientific notation - a way of conveniently representing large and small numbers.

2x10³ is the same as 2,000.
2x10⁹ = 2,000,000,000.

It is more compact than writing
"A proton masses 0.000,000,000,000,000,000,000,000,001,672,621,71kg," but it is exactly equivalent to 1.672,621,71x 10^-27kg.

 

[tech99]

I think the basis of the first understanding the proton was the cathode ray tube of Eugene Goldstein in 1886. In essence, the tube was a simple mass spectrometer, also used by J J Thompson to study the electron. I understand that the Penning trap was not made to work until 1959.

 

[ohwilleke]

It is also worth noting that the commonly quoted figure probably doesn't come from a single experiment, and it isn't necessarily the case that every measurement that goes into the final result comes from the same kind of experiment.

Instead it is a weighted average of the best available measurements from independent groups of scientists. Each measurement is assigned a weight equal to 1/uncertainty where the uncertainty is the uncertainty of the measurement (e.g. ± 0.03%).