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R̶e̶a̶d̶ ̶t̶h̶e̶ ̶c̶o̶n̶t̶e̶x̶t̶…̶ - A̶ ̶w̶a̶t̶t̶ ̶i̶s̶ ̶d̶e̶f̶i̶n̶e̶d̶ ̶a̶s̶ ̶1̶ ̶j̶o̶u̶l̶e̶ ̶p̶e̶r̶ ̶s̶e̶c̶o̶n̶d̶ ̶ A̶ ̶w̶a̶t̶t̶ ̶f̶o̶r̶ ̶1̶ ̶s̶e̶c̶o̶n̶d̶ ̶
by spacedcowboy 2y ago
R̶e̶a̶d̶ ̶t̶h̶e̶ ̶c̶o̶n̶t̶e̶x̶t̶…̶
- A̶ ̶w̶a̶t̶t̶ ̶i̶s̶ ̶d̶e̶f̶i̶n̶e̶d̶ ̶a̶s̶ ̶1̶ ̶j̶o̶u̶l̶e̶ ̶p̶e̶r̶ ̶s̶e̶c̶o̶n̶d̶
̶ A̶ ̶w̶a̶t̶t̶ ̶f̶o̶r̶ ̶1̶ ̶s̶e̶c̶o̶n̶d̶ ̶t̶h̶e̶r̶e̶f̶o̶r̶e̶ ̶e̶q̶u̶a̶l̶s̶ ̶1̶ ̶j̶o̶u̶l̶e̶,̶ ̶a̶ ̶m̶e̶a̶s̶u̶r̶e̶ ̶o̶f̶ ̶e̶n̶e̶r̶g̶y̶
- A̶ ̶T̶e̶r̶a̶w̶a̶t̶t̶ ̶f̶o̶r̶ ̶a̶ ̶d̶a̶y̶ ̶i̶s̶ ̶t̶h̶e̶r̶e̶f̶o̶r̶e̶ ̶a̶l̶s̶o̶ ̶a̶ ̶m̶e̶a̶s̶u̶r̶e̶ ̶o̶f̶ ̶e̶n̶e̶r̶g̶y̶.̶
[edit: The earth receives 14.9 ZettaWatts of solar power per day, and 173 Petawatts per second, I was reading it as 173 PW over a day, in which case the above works fine. Mea culpa]
See: https://gosolarquotes.com.au/amount-of-solar-energy-hitting-earth/ https://gosolarquotes.com.au/amount-of-solar-energy-hitting-...
- treyd 2y agoYeah the units cancel, that's the issue. The phrasing implies that after half a day it's received 85k terawatts which doesn't make any sense. Power (kg m^2 / s^3) * Time (s) = Energy (kg m^2 / s^2) Now from context it's obvious that what was meant is that Earth continually receives 170 terawatts from the sun. The phrasing is technically inaccurate, but it's a turn of phrase that works fine.
- deleted 2y ago[deleted]
- jessekv 2y agoso... close... petawatts ;)
- spacedcowboy 2y agoSo, not knowing any better, I read it as meaning 170k TW/day, so 85k TW/12 hours made sense to me, but you’re right… [1]. The earth receives 14.9 ZettaWatts of solar radiation per day… [1]: https://gosolarquotes.com.au/amount-of-solar-energy-hitting-earth/ https://gosolarquotes.com.au/amount-of-solar-energy-hitting-...
- deleted 2y ago[deleted]
- CorrectHorseBat 2y agoNo they don't, you need to divide, not multiply just like you would with every other unit. 1l of rain every day is 1l/day, not 1l * day . Which means Watt per day is J/s^2
- AlienRobot 2y agoI think a clearer example would be saying a car runs 20KM/H every day.
- gpderetta 2y agoOn the other hand batteries energy capacity is commonly rated in Watt hour. Watt*day is a perfectly cromulent energy statement although a bit misleading.
- Ekaros 2y agoWatt*day is weird, but at least unit of energy. Watts a day is not. Really common mistake in general to use kWh as a kW. Watthour is unit of energy. As watt is energy by time period. So you get back to units of energy. Technically watt/day could be change in power consumption.
- spacedcowboy 2y agoThat’s changing “every day” into “per day”. Judging by the downvotes that is how people are reading it, but “specified time” of a rate-quantity is an integration, to me. Which makes it a multiply op over the time specified. If you pour out one bucket of sand every hour, and you do that for 10 hours, I expect the quantity of sand to be measured in buckets.
- jijijijij 2y agoIf you want to be nitpicky about semantics, I think the only valid interpretation then is to take OP by their words and assume they meant energy transfer for 24h, since they did not write "per day" as you suggest: "Earth gets over 170,000 terawatts of solar energy every day" = 170 PW × 1d = 170 × P(J/s) × 86.4 × ks = 170 × 10¹⁵ × (J/s) × 86.4 × 10³ × s = 14.6 × 10²¹ × J = 14.6 ZJ However, I also think "of solar energy" could be read as specifying the type of energy for the "rate of energy transfer", which is already implied in 'watt'. And since it's related to energy usage (rate), there really is no need to leave the "rate of energy transfer" interpretation at all and get hung up on "energy vs. power": "Earth receives 170 petawatts as solar energy - 10,000 times the energy humanity uses, at any moment. Edit: And let's be real, we all only feel very smart here because we just watched the latest Technology Connections video https://www.youtube-nocookie.com/embed/OOK5xkFijPc https://www.youtube-nocookie.com/embed/OOK5xkFijPc :D
- deleted 2y ago[deleted]