Quote:
Originally Posted by mort
Hi sendler,
No, it is the road speed that matters the most. Power makes the thing go and the amount of power required at any speed depends on the speed.
If you use the ecomodder calculator here (note: the aero and rolling resistance forces are shown in Newtons) and think motorcycle... you get 30 hp needed to keep going 100 mph.
But the amount of power it takes to accelerate also depends on your speed. The acceleration is just like any other force being applied to the bike. Let's say you want to accelerate at 1 g, and you are going 50 mph. Again according to the ecomodder calculator, that would require 80 hp.
But how much power does it take to accelerate at 1 g at 100 mph. Your speed has doubled so the power has doubled: 160 hp.
So comparing the acceleration at 10 mph and 60 mph means comparing one condition with another that will require 6 times as much power - put another way: The same amount of power available at 10 mph and 60 mph will deliver 1/6th the acceleration.
Also I think the ecomodder calculator is wrong.
-mort |
This is incorrect. Your version of physics would make setting land speed records trivially easy.
The power required to overcome aerodynamic drag is not linear, but is instead a cubic function of speed. If it takes 20hp to overcome aerodynamic drag at 50mph, it will take you 160hp to overcome drag at 100mph. If you double your speed, you need eight times (2^3) the power to overcome aerodynamic drag. You also have to factor in rolling resistance and friction, although those are much smaller factors at higher speeds.
So, if you accelerate at 1g at 50mph and it takes 80hp (20hp due to aero drag, 60hp you accelerate your mass at 1g, ignoring rolling resistance), at 100mph you should require 220hp (160hp due to aero drag, 60hp to accelerate your mass at 1g).
Double this hypothetical car's speed again and it will take 1340hp to accelerate at 1g at 200mph.
The ecomodder calculator is valid, but can only give you accurate results if you provide accurate inputs (which are not always easy to determine).