driving on inclines

I'd take the one without the stop.

Tom

 

is it better to accel up hills to get them over with quicker?

 

If you can make it up the hill... go up. I've seen a few hills that my prius can't get over.... I had to back up the hill...

 

The velocity of your car will be the same whether you go down the steep hill or the more gently sloping one, since the height at which you depart is the same. In terms of going up, the same amount of total energy is used; however, if the steep hill is too steep you may get out of the efficiency range of the vehicle of the engine.

But this is all beside the point: I agree with qbee42 go with the one without the stop sign. When there is a choice, always pick the street without the stop sign.

 

I agree with qbee42 re: Avoid having to stop. And I agree with jps000 that the energy used will be roughly the same. However, coasting velocity is definitely affected by the grade, not the starting altitude, at least not near the surface of the earth. I believe you may be thinking of the acceleration of gravity in a vertical free fall, which is 32ft/sec**2 near the earths surface. I coast/glide down hills whenever I can, and the velocity or mph is defininately faster down the steeper grades. That's why you may even need to do the big No No and use the "B Mode".

 

What is the difference in distance between the routes?

 

"less steep":"steep"::3:1, as per original post.

 

I've not met the [legal street/paved] hill that my Prius cannot climb, yet.
I've even done the dreaded stop/start on Seattle streets (just a little steeper than Duluth streets, which I have driven on, too) heading up from the waterfront to I-5.

djphill, the secret to driving the Prius is not to drive it as though it has no gas pedal... drive it as though it has no brakes! (anticipate stops a long way off, coast as much as possible, no hard stops. Though, it has GREAT brakes, and will put you through the windshield!)

 

My understanding: velocity is the square root of 2gh, where g is gravity and h is height. The horizontal component (steepness of slope) does not matter. The equation does not account for friction effects, so the velocity could be smaller for the gentle slope, I guess, but then again as you gain great speed on the steep hill, you have to deal with draft effects. Also, remember, the end of the steep hill isn't the end of the distance he needs to travel. He also needs to travel 'flat' ground to get to the point where the gentle hill ends....

 

hello V8COBRA, how goes it? is there really a couple of hills your prius can't climb? i ask this honest question because mine has no problems. here in the LA area, i consider the BAXTER hill in echo park pretty "gnarly" in terms of a rather steep street to go over. yet, my prius can climb this from a dead stop.

now, for the san francisco prius owners, have you ever encountered a hill that your prius had problems with????????

 

I believe you are confusing the Coefficient of Discharge with the physics of an inclined plane Inclined plane - Wikipedia, the free encyclopedia

 

Well, you are right. I did not take into account the coefficient friction. I guess I'm stuck on the fact that the angle of friction will be less for the steep hill in the beginning, wider at the end. The gentle slope will have a wider angle of friction to begin and perhaps a narrower one at the end.

 

That's O.K. That's what I like about PC. There's usually someone around to clarify things. They've set me straight on more than one thing. I enjoy learning. I thought maybe you lived in Oklahoma or Florida, flatland. But I figured in Connecticut you surely must have noticed that you needed less gas or more braking, the steeper the downhill, to maintain speed. We were just up in Connecticut this spring, Watertown. Beautiful state. Thanks for the reply.

 

Since this has turned into a physics discussion, I'll chime in. The confusion about the effect of the hill's angle has to do with power verse energy. When you descend a hill, the same amount of energy is converted from potential to kinetic, regardless of the angle. In other words, if you drop 400 vertical feet, you release the same amount of energy falling straight down or going down a 1% grade. On the other hand, it's going to take a lot longer to coast down the 1% grade, so the power is a lot lower. Power is work over time. In this case the work is the amount of energy released going downhill, and time is the time it takes to get to the bottom. The steeper the hill, the shorter the time, so the higher the power. You have to brake a lot harder to make up for the higher power, but you do it for a shorter period of time, so the energy comes out equal.

Real world friction complicates the discussion a bit. If you drive your Prius off of a cliff, you have no rolling resistance and higher wind resistance, but for a shorter time. A long incline keeps the speed low, so the velocity squared loss of wind resistance is much lower, but you do get more rolling resistance. The break even point will be where the sum of the two are lowest.

Tom

 

Agreed on about liking PC! Helpful discussions.

Are we talking about the same thing? I fully agree about the steeper hill point, of course it's faster and more braking is needed.

The issue is that we are not talking about a steep hill and a gentle hill experience, but the total distance traveled. Say you travel 2 miles The steep hill is much faster for 1 mile, but then you will be much slower on the flats for the 2nd mile. On the gentle hill, you will never reach the speed of the steep hills, but you will be faster than the flat part of the steep hill route... Also, I find significant aerodynamic drage at higher speeds, so I'm not sure this question has been answered...

 

Yes, wind resistance vs. rolling resistance. So, how does it all add up, when you are not comparing inclines but distance traveled, with steep + fatter vs. gentle all the way....

 

qbee42: Everything you say is correct, but I was responding to jps000's claim above that the velocity will be the same regardless of the angle of the incline.

 

Are you kidding? I've never had that problem before