# Physics question for you guys

#### iamwiz82

##### Lifer
If an closed air system connected to 4 tires on a car with equal weight front, rear, and sides is set so that all the tires valves are open and equalized at 30PSI and a load is added to the back(say 2000lbs more) would the pressure in the rear tires change at all? We are having a discussion about this on another board and I would like to know.

#### FoBoT

##### No Lifer
you mean the air pressure in the tires?
if its a closed system, then no

the pressure can change due to either the temperature changing, or the volume of gas inside the closed system changing, or the size of the system changing

i think

you are making my brain hurt

Ideal Gases under Constant Volume, Constant Pressure, Constant Temperature, & Adiabatic Conditions

this one jarred my memory

pv/T=n

pressure times volume divided by temperature equals moles

well, are you assuming the air isn't compressable? air is compressable, but ...

my brain just exploded!!!!!!!!! :Q

This relationship between pressure and volume is called Boyle's Law in honor of Robert Boyle who first observed it in 1660. Finally, if the mass and pressure are held constant, the volume is directly proportional to the temperature for an ideal gas. This relationship is called Charles and Gay-Lussac's Law in honor of the two French scientists who discovered the relationship.
In the mid 1600's, Robert Boyle studied the relationship between the pressure and the volume of a confined gas held at a constant temperature. Boyle observed that the product of the pressure and volume are observed to be nearly constant. (The product of pressure and volume is exactly a constant for an ideal gas.) This relationship between pressure and volume is called Boyle's Law in his honor. For example, suppose we have a theoretical gas confined in a jar with a piston at the top. The initial state of the gas has a volume equal to 4.0 cubic meters and the pressure is 1.0 kilopascal. With the temperature and number of moles held constant, weights are slowly added to the top of the piston to increase the pressure. When the pressure is 1.33 kilopascals the volume decreases to 3.0 cubic meters. The product of pressure and volume remains a constant (4 x 1.0 = 3 x 1.33333 ).
The relationship between temperature and volume, at a constant number of moles and pressure, is called Charles and Gay-Lussac's Law in honor of the two French scientists who first investigated this relationship. Charles did the original work, which was verified by Gay-Lussac. They observed that if the pressure is held constant, the volume is equal to a constant times the temperature. For example, suppose we have a theoretical gas confined in a jar with a piston at the top. The initial state of the gas has a volume qual to 4.0 cubic meters, and the temperature is 300 degrees Kelvin. With the pressure and number of moles held constant, the burner has been turned off and the gas is allowed to cool to 225 degrees Kelvin. (In an actual experiment, a cryogenic ice-bath would be required to obtain these temperatures.) As the gas cools, the volume decreases to 3.0 cubic meters. The volume divided by the temperature remains a constant (4/300 = 3/225 ).

i have no idea!!!!

i learned that stuff in 1987

#### Lithium381

##### Lifer
i think the pressure would stay the same....on the tire, but there would be more on the ground? yikes, i haven't done something lke this in months...

#### Hayabusa Rider

##### Admin Emeritus & Elite Member
Let me see if I understand the problem. You have 4 tires and they are all connected to each other so air can flow freely? If this is true, the pressure in ALL the tires changes, because you do not have 4 tires, you have 1 container of a very unusual shape. The weight increases pressure, but the air redistrubutes.

#### iamwiz82

##### Lifer
Originally posted by: Hayabusarider
Let me see if I understand the problem. You have 4 tires and they are all connected to each other so air can flow freely? If this is true, the pressure in ALL the tires changes, because you do not have 4 tires, you have 1 container of a very unusual shape. The weight increases pressure, but the air redistrubutes.

so the pressure in all 4 tires would increase?

#### Moonbeam

##### Elite Member
I don't know, but you would thing the pressure would rise in all tires as the back ones flattened. I would guess that since the volume can't really change that much, the tires do go flat a bit, the inner surface of the enclosed system divided into 2000 ought to be about how much it goes up. It's an interesting question. It seems like the load is distributed all over the inside of the tire. I would think it would be very much like deflating an air mattress by laying on it. Your weight increases the pressure and deflates it faster.

#### Hayabusa Rider

##### Admin Emeritus & Elite Member
Absolutely. Think of a cylindrical balloon

Squeeze one end, then it deforms, but the pressure at the point where you squeeze isnt higher than anywhere else.

Now with the tires, they have relatively fixed volume, so increasing the force on them causes the pressure to go up, and the pressure equalizes just as with the balloon. Might take a few moments, because the lines restrict flow, but do not eliminate it.

That work for you?

#### Moonbeam

##### Elite Member
Yup the pressure in all increases because all tires are connected. Blow into a straw and the air comes out the other end.

#### TomBilliodeaux

##### Senior member
Yes, increase.
Remember units. ....Lb per square inch. Force / area.

If you add 2000 lb. force, the resultant reaction must be 2000 lbs in the opposite direction for equilibrium.

#### Moonbeam

##### Elite Member
I wonder if this explains how a butterfly flapping its wings in Africa can cause a hurricane in Florida, not that I have much use for Florida.

#### Hayabusa Rider

##### Admin Emeritus & Elite Member
Few would be able to sit through that explanation M. I havent the heart for that, although I could reserve it as a blackmail threat

#### tweakmm

##### Lifer
Originally posted by: Moonbeam
I wonder if this explains how a butterfly flapping its wings in Africa can cause a hurricane in Florida, not that I have much use for Florida.
the theory of chaos is very interesting... maybe if we got a really big butterfly...

#### Moonbeam

##### Elite Member
Then I'd best decline. No use causing chaos.

#### Moonbeam

##### Elite Member
dang you, tweakmm, you tipped my hand.

#### lowtech1

##### Diamond Member

The volume of air doesn't change therefor no pressure increase. The tire may deform to take on the added weight because wall is what takes the weight & transfers that force onto the ground that is directly underneath it.

You can test that theory out using a strong balloon & a pressure gauge.

#### Hayabusa Rider

##### Admin Emeritus & Elite Member
Originally posted by: lowtech
The volume of air doesn't change therefor no pressure increase. The tire may deform to take on the added weight because wall is what takes the weight & transfers that force onto the ground that is directly underneath it. You can test that theory out using a strong balloon & a pressure gauge.

So you are saying that if I stand on a basketball the pressure does not increase. If that is true, then I can put an infinite amount of weight on the ball and it will not rupture

#### Moonbeam

##### Elite Member
Also you could try laying down and dropping a two thousand pound slab of concrete on your body and see what it does to your eyes.

#### tweakmm

##### Lifer
Originally posted by: Moonbeam
Also you could try laying down and dropping a two thousand pound slab of concrete on your body and see what it does to your eyes.
look out California!

#### Hayabusa Rider

##### Admin Emeritus & Elite Member
Originally posted by: Moonbeam
Also you could try laying down and dropping a two thousand pound slab of concrete on your body and see what it does to your eyes.

I KNEW you were an experimental physicist!!!

#### Moonbeam

##### Elite Member
Hay tweak, I just invented a lowtech eye launcher. A site for sore eyes.

#### Moonbeam

##### Elite Member
I thought the eye in the sky was more applied physics than theoretical, but I'll take what I can get. The meat mallat and the plastic mustard jar were my early triumphs.

#### notfred

##### Lifer
Yes, the pressure in the tires will increase. For an illustration of the concept:

Take a ball and fill it with air so that it's slightly limp (kinda flat, but not totally flat... still msotly round, if you get the idea). Now attach an air pressure guage to it. No pressure, right?

Drop your 2000lb weight on the ball. Look at the air pressure guage again.

#### lowtech1

##### Diamond Member

/me go hide head in sand