Poundals to dynes: two absolute systems meet
Neither side needs gravity
This is the one pairing in the category where no reference to gravity appears on either side. The poundal is the absolute unit of the foot-pound-second system; the dyne is the absolute unit of the centimetre-gram-second system. Each is assembled from a base mass and a base acceleration, and the factor joining them is nothing but arithmetic on the pound, the foot and the gram. One poundal is 13825.5 dynes, and one dyne is 0.00007233 poundal.
What the twentieth century actually chose
Both systems were devised by people who wanted mechanics without a hidden constant. CGS won the early argument, largely because the centimetre and the gram made laboratory quantities produce tidy numbers, and the dyne became the working unit of physics for decades. The FPS system kept the poundal but never displaced the gravitational units commerce preferred. When SI arrived, the metre and the kilogram were large enough to justify the newton, and both absolute ancestors were retired.
Poundal to dyne equivalents
Values that show the sheer scale of the dyne, which turns almost any machinery-sized force into a five-figure number.
| Poundal (pdl) | Dyne (dyn) |
|---|---|
| 1 | 13825.4954376 |
| 10 | 138254.954376 |
| 25 | 345637.38594 |
| 50 | 691274.77188 |
| 100 | 1382549.54376 |
| 1000 | 13825495.4376 |
Why absolute measurement was the real preference
The point of an absolute system is that a force can be written purely in terms of mass, length and time, so an equation stays true wherever it is used. A gravitational system must assume a value for g, which makes one calculation give different answers at different latitudes until a standard value is imposed. That is the twentieth century preference in its real form: not metric over imperial, but definition over locale.
Five orders of magnitude
The dyne is minute — the force that accelerates a gram by a centimetre per second squared — so poundal figures become large when written out in dynes. Expect five digits for almost any everyday value. Shifting the decimal point five places to the right is a fair mental estimate, since 13825.5 is close enough to ten to the fifth power.
Frequently asked questions
Are poundals and dynes both absolute units?
Yes, and that is what makes this pair unusual. Each is defined by a base mass and a base acceleration with no reference to gravity anywhere: the poundal from the pound and the foot, the dyne from the gram and the centimetre. Neither changes value with latitude.
What arithmetic connects the pound and the foot to the dyne?
A base-mass ratio and a base-acceleration ratio, multiplied together. The pound is 453.59237 grams and the foot is 30.48 centimetres, so the force ratio is that product, giving 13825.5 dynes to the poundal. No measured constant enters anywhere.
Which of the two is the larger force?
The poundal, by a wide margin — about fourteen thousand times larger. The dyne is deliberately tiny because it was built for laboratory work on grams and centimetres, where quantities are minute, while the poundal was built for masses on the scale of machinery.
Why did the dyne outlast the poundal in scientific use?
Because CGS was the working system of physics for decades, and the dyne fitted the scale of the experiments being performed. It gave way only when SI made the metre and the kilogram the base units and the newton replaced it, a change that took until the 1960s to become general.
What does the CGS system have that the foot-pound-second system lacked?
Nothing in principle — both are coherent absolute systems with a matching unit for every mechanical quantity. The difference was adoption. CGS became the common language of laboratories, so its units were taught, tabulated and cited in journals, and that is how a system wins.