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In rec.aviation.piloting Ernest Christley wrote:
wrote: In rec.aviation.piloting Ernest Christley wrote: wrote: The laws of physics say once an object is in motion it takes no energy to maintain the velocity UNLESS there is some other force at work that would cause the velocity to decrease. Since at a constant speed, the a in F=ma is zero, the force is zero no matter the mass. Once at speed in a car (or airplane or rocket ship) the only energy needed to maintain speed is that equal to any drag forces that would otherwise slow the car down. Have you looked at the current crop of high mileage cars? They all have very aerodynamic profiles to get the air drag down. They also have very narrow, hard tires. Unfortunately, the DOT has laws against solid rubber tires or they could be made even harder. Your analysis would be mostly correct if we were talking about trains. My analysis of what? The biggest source of drag on a car is air followed by tires. Of course the makers are going to put hard tires on as well as streamline the vehicle to get mileage up. The less drag, the less gas the vehicle uses. What's your point? The point is that weight matters...even in land-locked vehicles. In cars, weight matters most in acceleration and doesn't matter in any significant amount with modern tires in cruise. -- Jim Pennino Remove .spam.sux to reply. |
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In cars, weight matters most in acceleration and doesn't matter in any significant amount with modern tires in cruise. Speculate please: 1. Two 3,600 lb cars - good tires 2. Traveling 60 mph (no wind) 3. 4cly - 150 hp (Honda Accords) 3. Flat highway in North Dakota 4. Fuel flow meters hooked up to both vehicles (Honda #1) Driver ................ 105 lbs Fuel .................... 15 lbs TOTAL .............. 120 lbs (1/30th of 3,600 lb car) (Honda #2) Driver ................. 300 lbs Passengers ........ 700 lbs Luggage ............. 100 lbs Fuel ................... 100 lbs TOTAL ............. 1,200 lbs (1/3 of 3,600 lb car) ....BTW, BTDT! g If both vehicles were monitored for 50 miles, would their fuel flow be (approx) the same, in cruise? Paul-Mont |
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In rec.aviation.piloting Montblack wrote:
wrote) In cars, weight matters most in acceleration and doesn't matter in any significant amount with modern tires in cruise. Speculate please: 1. Two 3,600 lb cars - good tires 2. Traveling 60 mph (no wind) 3. 4cly - 150 hp (Honda Accords) 3. Flat highway in North Dakota 4. Fuel flow meters hooked up to both vehicles (Honda #1) Driver ................ 105 lbs Fuel .................... 15 lbs TOTAL .............. 120 lbs (1/30th of 3,600 lb car) (Honda #2) Driver ................. 300 lbs Passengers ........ 700 lbs Luggage ............. 100 lbs Fuel ................... 100 lbs TOTAL ............. 1,200 lbs (1/3 of 3,600 lb car) ....BTW, BTDT! g If both vehicles were monitored for 50 miles, would their fuel flow be (approx) the same, in cruise? A pulled out of my ass, wild assed guess is that since you are increasing the load by 33%, then yes, you will see a difference, and at that loading the tires will be visibly deformed. Now, would you care to calculate the energy required to accelerate 3720 pounds to 60 mph versus accelerating 4800 pounds to 60 mph? Assume gasoline is 45 megajoules per kilogram and the engine is 38% efficient. You may neglect all drag for this calculation and express the energy in kilograms of gasoline. -- Jim Pennino Remove .spam.sux to reply. |
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