Excellent Article Explaining "Polar Moment of Inertia"
11-14-2000, 10:30 PM
#21
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Originally posted by cmnsnse:
Back to the ice skater I also think thats a bad analogy just because a skater can bring their mass closer to the axis, whereas the car cannot, the car is easier to spin but also easier to stop spinning.
A fun thing to do is grab two gallon jugs of water and sit in a rotating chair and spin with the jugs held at arms legnth, when you're done getting yourself going bring the jugs in towards the center point, you will accelerate like the skaters. What happens is that since it takes less energy to spin the same amount of mass that is closer to the axis, if you put x amount of energy into it with the mass towards the outer point then when you bring them in you will accelerate to the rate that you would get if you applied x amount of energy to the inner most position.
whats the point? I dunno.
Just means this car is cool, Im glad I was awake during physics.
I like roast beef. . .
Back to the ice skater I also think thats a bad analogy just because a skater can bring their mass closer to the axis, whereas the car cannot, the car is easier to spin but also easier to stop spinning.
A fun thing to do is grab two gallon jugs of water and sit in a rotating chair and spin with the jugs held at arms legnth, when you're done getting yourself going bring the jugs in towards the center point, you will accelerate like the skaters. What happens is that since it takes less energy to spin the same amount of mass that is closer to the axis, if you put x amount of energy into it with the mass towards the outer point then when you bring them in you will accelerate to the rate that you would get if you applied x amount of energy to the inner most position.
whats the point? I dunno.
Just means this car is cool, Im glad I was awake during physics.
I like roast beef. . .
That said... go drive.
11-14-2000, 10:56 PM
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[QUOTE]Originally posted by S2WOOOW:
[B]I'm just trying to reply to the authors implication that a mid engine car would handle better because of it's low moment of inertial about its center of rotation (I think he really means the center of gravity, the only way to get the center of rotation of a car near the geometric center of the car is to have 4wheel steering, or take the car into space and spin it).
[B]I'm just trying to reply to the authors implication that a mid engine car would handle better because of it's low moment of inertial about its center of rotation (I think he really means the center of gravity, the only way to get the center of rotation of a car near the geometric center of the car is to have 4wheel steering, or take the car into space and spin it).
11-14-2000, 11:24 PM
#24
bb, S2W is pointing out the fact that the front and rear tires don't travel the same path. In a slalom the car does not simply translate side to side, there is yaw with the front swinging more than the rear (based on wheel base, not center of gravity). This implies the yaw center is somewhere behind mid-point of wheel base.
I think that's what he's trying to convey to you at least
I think that's what he's trying to convey to you at least
11-15-2000, 09:40 AM
#26
Ahhh, busting out with the old Parallel-Axis Theorem, you got all the good ones on tap.
S2W's application would use a smaller "d" (distance) term and since it is the squared term in this illustrious equation, could amount to a significant difference,..., of opinion.
S2W's application would use a smaller "d" (distance) term and since it is the squared term in this illustrious equation, could amount to a significant difference,..., of opinion.
11-15-2000, 12:08 PM
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[QUOTE]Originally posted by RT:
[B]Ahhh, busting out with the old Parallel-Axis Theorem, you got all the good ones on tap.
S2W's application would use a smaller "d" (distance) term and since it is the squared term in this illustrious equation, could amount to a significant difference,..., of opinion.
[B]Ahhh, busting out with the old Parallel-Axis Theorem, you got all the good ones on tap.
S2W's application would use a smaller "d" (distance) term and since it is the squared term in this illustrious equation, could amount to a significant difference,..., of opinion.
11-15-2000, 01:38 PM
#29
bb, the reason I keep asking you about the 928 is because you can have the same mass and center of gravity (50/50) but a significantly different MOI (polar). Yes? 
Assume a mid and a rear have the same mass and have the same wheelbase. Both have a 50/50 split. Both have identical inertia. From a pure physics standpoint the cars will react the same, neglecting suspension differences and the like.
11-15-2000, 02:22 PM
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[QUOTE]Originally posted by RT:
[B]bb, the reason I keep asking you about the 928 is because you can have the same mass and center of gravity (50/50) but a significantly different MOI (polar).
[B]bb, the reason I keep asking you about the 928 is because you can have the same mass and center of gravity (50/50) but a significantly different MOI (polar).