4 ms·

"Maybe, but the fact that a high end commercial microwave is about the same amount of power as my car rolling along at about 30mph(45kph) on a level road would

"Maybe, but the fact that a high end commercial microwave is about the same amount of power as my car rolling along at about 30mph(45kph) on a level road would have surprised my intuition initially. I would have pegged a car for MUCH higher power output." Well, I think most people don't have an intuition for whatever a "high end commercial microwave" is. I would expect a car on a level highway to be using on the order of 10 hp. I'm sure my microwave uses far less.

labawi 7y ago
Air resistance is proportional to speed squared, meaning (air resistance component of) energy per distance is ~ speed², and energy per second is ~ speed³. 45 km/h vs. 90 km/h is almost an 8-fold difference of power to sustain. Air resistance is not the dominant factor on lower speeds, so I'd guesstimate it at 6-7x. At 130km/h, with 33.6 MJ/l gasoline energy content, at 7l/100km, you get: 9.1l/h -> 300 MJ/h -> 84kW. At 30% efficiency you get 25kW or 33hp. That's about a dozen microwaves. At 45km/h, air resistance power use should be about 1/24 of 130km/h. Guesstimating total consumption as 1/10, you get around 2kW, or a single (240V 10A) microwave/kettle.
- perl4ever 7y ago
  Going at a steady 30 mph on a straight, level road is not really something people do in my part of the world, so I can't say that I have experience to know what sort of gas mileage you'd get. Edit: More research suggests that gas mileage should be similar between 30 and 60 mph, it kind of plateaus, but I guess that means power required would still go up proportionally. 10 hp is something I was remembering from reading something about driving at around 60, so I guess 30 mph should take 5 hp.
  - mrguyorama 7y ago
    In about the 80s, cars were rather more efficient at 50mph. Depending on brand, market segment, and transmission, I'd believe they are roughly as fuel efficient at higher speeds. My car (2.0L turbocharged hatchback) uses about 7-14kw to maintain 60-70mph on level ground at around 30-33mpg. The unfortunate uncertainty in my figures is due to poor memory

labawi 7y ago

Air resistance is proportional to speed squared, meaning (air resistance component of) energy per distance is ~ speed², and energy per second is ~ speed³. 45 km/h vs. 90 km/h is almost an 8-fold difference of power to sustain. Air resistance is not the dominant factor on lower speeds, so I'd guesstimate it at 6-7x. At 130km/h, with 33.6 MJ/l gasoline energy content, at 7l/100km, you get: 9.1l/h -> 300 MJ/h -> 84kW. At 30% efficiency you get 25kW or 33hp. That's about a dozen microwaves. At 45km/h, air resistance power use should be about 1/24 of 130km/h. Guesstimating total consumption as 1/10, you get around 2kW, or a single (240V 10A) microwave/kettle.

perl4ever 7y ago
Going at a steady 30 mph on a straight, level road is not really something people do in my part of the world, so I can't say that I have experience to know what sort of gas mileage you'd get. Edit: More research suggests that gas mileage should be similar between 30 and 60 mph, it kind of plateaus, but I guess that means power required would still go up proportionally. 10 hp is something I was remembering from reading something about driving at around 60, so I guess 30 mph should take 5 hp.
- mrguyorama 7y ago
  In about the 80s, cars were rather more efficient at 50mph. Depending on brand, market segment, and transmission, I'd believe they are roughly as fuel efficient at higher speeds. My car (2.0L turbocharged hatchback) uses about 7-14kw to maintain 60-70mph on level ground at around 30-33mpg. The unfortunate uncertainty in my figures is due to poor memory