Sorry, yeah I meant psi.
And yeah, pressure units annoy the hell out of me too. There’s psi, kPa, Barr, Torr, atm, mmH20, in. Hg, and so on. It’s dumb.
That is an excellent point. Yeah, PSI would totally read as pounds times square inches which would be something else entirely. Adding in the extra P would fix it, too. PPSI. Suppose it’s another thing that people just have to get used to, haha.
Eh, it’s pretty unambiguous. kW/hour is a pretty useless unit. Power surges may be measured in kW/s or something, but they don’t really have any impact over a span of more than a couple seconds.
Likewise, pounds times square inches is equivalent go kg*m3/s2 in SI units - which also seems pretty meaningless. Maybe there is a use for it?
What really grinds my gears is that pounds are a unit of mass, not force. The “pounds” in “pounds per square inch” is short for “pounds-force“. It’s the force of one pound of mass accelerating at 1g. Preposterous.
Wait wait Wait, can you give me more on this kWh thing? I thought I understood this already.
A single kW is a unit of power, literally 1000 watts.
A kWh is a unit of energy, as in stored or delivered.
Draw 500 watts for 2 hours? That’s a kWh.
Or have a battery that can hold 1 kWh, then assuming 100% efficiency you could draw 1000 watts from it for an hour before it was empty.
All of this is kW times hour, I would say?
But in my mind I would interchangeably say per hour as well, they feel the same.
If you use exactly 20 kW for an hour, it will translate to 20 kWh. But if your power usage varies over time, you can’t keep track of it so simple. It’s just how it is.
The unit is really watt [W] and the Greek prefix kilo (k) for 1000. This way it’s fast and easy to convert to different scales (like Mega, Giga etc) for comparing numbers
A watt is a derived unit for a rate of change, an amount of energy used in a unit of time, so P = E / t. A kW per hour would be a rate divided by time, or E / t^2, resulting in another rate.
More colloquially, think of watts/power by analogy to another rate, that of speed. Moving at a speed of 100kph for 3 hours results in 300 speed-hours of distance. Saying 100 kilometers per hour per 3 hours sounds awkward, but is actually a weird way to say acceleration, a rate of change of speed. (And probably a hint to get your car serviced.)
Anyway, the key is to think of a kilowatt as a rate, not a quantity.
Generally speaking you can hold in the valve for 60 seconds to let out enough air from your street pressure for off-road. It’s better to measure and you really want a 12v compressor to reinflate for the ride home but in a pinch…
As an Aussie I’ve used metric for everything my whole life, but I’ve just realised that everything I’ve ever used to inflate stuff has been metered in PSI. I just know that ~30PSI is good for tyres, ~15PSI is good for soccer balls.
I wouldn’t know the conversions because there’s no use for it because that’s not what the pumps use. Weird.
I guess you’re talking about psi.
(No offense to you, dear Buffaloaf, I just looked it up and thought I might share).
For everyone of the 191 non-USA countries, 10 psi is 0,69 bar or 690 hPa. That’s pretty low.
By the way, why is psi written in such a weird way? It should be lbs/ in^2
Sorry, yeah I meant psi. And yeah, pressure units annoy the hell out of me too. There’s psi, kPa, Barr, Torr, atm, mmH20, in. Hg, and so on. It’s dumb.
Yeah same I was inflating all the bicycle tires of my family. On most of the tires it says inflate to x bar, but my electric pump only knows psi.
Because in^2 is generally said “square inches.”
So it’s “pounds per square inch.”
Sometimes “per” will get its own letter, like in PPM - parts per million - and sometimes it’s left off, as in PSI.
And why?
Because we said so.
Thanks, friend :)
I know how it comes to be, I just think it’s stupid.
For example, kW times h is not the same as kW per hour. That’s why kWh means kilowatt times hour.
If I wrote ms to denote meters per second that would create massive confusion.
That is an excellent point. Yeah, PSI would totally read as pounds times square inches which would be something else entirely. Adding in the extra P would fix it, too. PPSI. Suppose it’s another thing that people just have to get used to, haha.
Eh, it’s pretty unambiguous. kW/hour is a pretty useless unit. Power surges may be measured in kW/s or something, but they don’t really have any impact over a span of more than a couple seconds.
Likewise, pounds times square inches is equivalent go kg*m3/s2 in SI units - which also seems pretty meaningless. Maybe there is a use for it?
What really grinds my gears is that pounds are a unit of mass, not force. The “pounds” in “pounds per square inch” is short for “pounds-force“. It’s the force of one pound of mass accelerating at 1g. Preposterous.
Wait wait Wait, can you give me more on this kWh thing? I thought I understood this already.
A single kW is a unit of power, literally 1000 watts.
A kWh is a unit of energy, as in stored or delivered. Draw 500 watts for 2 hours? That’s a kWh. Or have a battery that can hold 1 kWh, then assuming 100% efficiency you could draw 1000 watts from it for an hour before it was empty.
All of this is kW times hour, I would say? But in my mind I would interchangeably say per hour as well, they feel the same.
Obviously I’m wrong, but I’d like to know why lol
If you use exactly 20 kW for an hour, it will translate to 20 kWh. But if your power usage varies over time, you can’t keep track of it so simple. It’s just how it is.
The unit is really watt [W] and the Greek prefix kilo (k) for 1000. This way it’s fast and easy to convert to different scales (like Mega, Giga etc) for comparing numbers
A watt is a derived unit for a rate of change, an amount of energy used in a unit of time, so P = E / t. A kW per hour would be a rate divided by time, or E / t^2, resulting in another rate.
More colloquially, think of watts/power by analogy to another rate, that of speed. Moving at a speed of 100kph for 3 hours results in 300 speed-hours of distance. Saying 100 kilometers per hour per 3 hours sounds awkward, but is actually a weird way to say acceleration, a rate of change of speed. (And probably a hint to get your car serviced.)
Anyway, the key is to think of a kilowatt as a rate, not a quantity.
Generally speaking you can hold in the valve for 60 seconds to let out enough air from your street pressure for off-road. It’s better to measure and you really want a 12v compressor to reinflate for the ride home but in a pinch…
As an Aussie I’ve used metric for everything my whole life, but I’ve just realised that everything I’ve ever used to inflate stuff has been metered in PSI. I just know that ~30PSI is good for tyres, ~15PSI is good for soccer balls.
I wouldn’t know the conversions because there’s no use for it because that’s not what the pumps use. Weird.