Peter,
I probably created some confusion by trying to say too much at once
regarding the horsepower versus speed concept. Let me amplify that part a
little. Rolling resistance times speed means it takes twice as much power
to maintain a constant speed at 60 versus 30. Wind resistance goes as speed
squared, so the power to overcome wind resistance is speed times speed
squared, or speed cubed. That's why over about 60 mph wind resistance
becomes the predominant factor. Finally, regarding acceleration, the force
is mass times acceleration. This means, for a given mass/weight of car, the
force it takes to produce a particular acceleration is constant. So, as
with the other factors, when you multiply this force times the speed of the
car, you get the horsepower needed; i.e., the power needed for a given
acceleration also increases in direct proportion to speed.
Hope you have a good one,
Bob
|