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Post by xinacrisp on Jan 27, 2010 1:57:54 GMT -4
I don't think that air resistance features much when it comes to braking, unless you use a chutte or are in a plane.
Air resistance does have influence, off course not at 30 MPH, but if you go like 160 MPH it does influence the breaking because it changes the downforce of the vehicle, changing the friction between the tires and the ground. when a car is in another car slipstream both accelaration and braking suffer from the lack of air resistance, for example notice that when 2 F1 cars go at full speed in a straight way notice that the 1 that is in the slipstream pulls out off it just before it hit the brakes
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Post by bazbear on Jan 27, 2010 4:23:10 GMT -4
Braking in autos is all about devices slowing down the wheels, then how much friction the tires/tyres wrapped around those wheels can get on the surface they are traveling on. Down force and lift effect it minimally, other than in high performance cars here on earth; and as the moon has no atmosphere, they never into it there.
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Post by xinacrisp on Jan 27, 2010 5:26:26 GMT -4
Braking in autos is all about devices slowing down the wheels, then how much friction the tires/tyres wrapped around those wheels can get on the surface they are traveling on. Down force and lift effect it minimally, other than in high performance cars here on earth; and as the moon has no atmosphere, they never into it there.
From wikipedia:"The term downforce describes the downward pressure created by the aerodynamic characteristics of a car that allows it to travel faster through a corner by increasing the pressure between the contact area of the tire and the road surface, thus creating more grip."
So my point is, no air resistence on the moon = no down force/downforce = less grip on the tyres = longer braking distance.
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Post by gwiz on Jan 27, 2010 7:56:45 GMT -4
So my point is, no air resistence on the moon = no down force/downforce = less grip on the tyres = longer braking distance. While this is strictly true, aerodynamic forces vary with the square of the velocity, so will be pretty small on earth at the low speed of the lunar rover. The main effects on braking will be the lower grip due to lower gravitational downforce, countered by the higher rolling resistance of driving on a loose surface.
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Jason
Pluto
May all your hits be crits
Posts: 5,579
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Post by Jason on Jan 27, 2010 12:28:16 GMT -4
And guns won't shoot accurately because there is no air to stabilise the spinning bullet and they will just go off in random directions. ...actually read that on a forum a long time ago. That doesn't sound correct to me. Isn't the bullet spinning creating gyroscopic stabilization from the mass of the bullet itself, which doesn't depend in any way on the air?
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Post by Jason Thompson on Jan 27, 2010 12:48:54 GMT -4
Indeed. Many satellites use spin-stabilisation, so it doesn't depend on the air.
Additionally, the bullet will still go in the same direction whether it is spin-stabilised or not, since the direction is determined by the barrel of the gun. It's not going to suddenly shoot off in a different direction once it exits the gun. Mythbusters showed this quite nicely when they used a variety of means to remove the spin-stabilisation of bullets. They cartwheeled and hit targets side-on rather than nose-first, but they still travelled in the same direction.
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Post by echnaton on Jan 27, 2010 15:04:52 GMT -4
And guns won't shoot accurately because there is no air to stabilise the spinning bullet and they will just go off in random directions. ...actually read that on a forum a long time ago. That doesn't sound correct to me. Isn't the bullet spinning creating gyroscopic stabilization from the mass of the bullet itself, which doesn't depend in any way on the air? I think Chew was replying in kind to PW's joking post just above his.
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Post by PhantomWolf on Jan 27, 2010 15:56:57 GMT -4
I don't think that air resistance features much when it comes to braking, unless you use a chutte or are in a plane.Air resistance does have influence, off course not at 30 MPH, but if you go like 160 MPH it does influence the breaking because it changes the downforce of the vehicle, changing the friction between the tires and the ground. when a car is in another car slipstream both accelaration and braking suffer from the lack of air resistance, for example notice that when 2 F1 cars go at full speed in a straight way notice that the 1 that is in the slipstream pulls out off it just before it hit the brakes Well true, but then since the LRV only got up to about 12 MPH and had a total of zero aerodynamic surfaces, I think we can safely discount any difference in braking distance due to the air, or lack of.
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Jason
Pluto
May all your hits be crits
Posts: 5,579
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Post by Jason on Jan 27, 2010 16:14:24 GMT -4
That doesn't sound correct to me. Isn't the bullet spinning creating gyroscopic stabilization from the mass of the bullet itself, which doesn't depend in any way on the air? I think Chew was replying in kind to PW's joking post just above his. I thought about that, but then it sounded like something someone might actually believe.
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Post by PhantomWolf on Jan 27, 2010 17:12:27 GMT -4
I think Chew was replying in kind to PW's joking post just above his. I thought about that, but then it sounded like something someone might actually believe. The unfortunate thing is that both Chew and I were using things that people have actually claimed.
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Post by echnaton on Jan 27, 2010 21:24:29 GMT -4
I think Chew was replying in kind to PW's joking post just above his. I thought about that, but then it sounded like something someone might actually believe. You can never be sure in the debunking game.
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Post by chew on Jan 28, 2010 11:04:10 GMT -4
I thought about that, but then it sounded like something someone might actually believe. You can never be sure in the debunking game. Too true. I can't remember which forum the discussion was on, but the inaccurate spinning bullet in a vacuum claim was met with far too much acceptance, and exclusively by the "gun enthusiasts" on the forum, at that. Is it just me, or is scientific literacy inversely proportional to the square of the number of guns a person owns?
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Post by echnaton on Jan 28, 2010 11:55:10 GMT -4
While perhaps being an outlier, I own two dozen guns ranging from a dainty pearl handled ladies pistol to a 50 caliber muzzle loader yet am above average in scientific literacy. Most of the weapons are antiques but several are modern.
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Jason
Pluto
May all your hits be crits
Posts: 5,579
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Post by Jason on Jan 28, 2010 12:25:17 GMT -4
Is it just me, or is scientific literacy inversely proportional to the square of the number of guns a person owns? That would be just you.
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Post by chew on Jan 28, 2010 13:20:53 GMT -4
Is it just me, or is scientific literacy inversely proportional to the square of the number of guns a person owns? That would be just you. Good. I was beginning to worry.
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