Question

In a hot summer day, i filled the tires of my car with 2.7 bar.
If i placed my car or drove it to Kilimanjaro or any other big mountain , what is the pressure inside the tires now?
And if in the next day, at same place, it started to rain, and wasn't hot anymore, what was the pressure now?

Answer 1

@shubhamsrg
@ghazi
@Hero
@hba
@hartnn

Answer 2

I will not tell you.

Answer 3

lol

Answer 4

why

Answer 5

Because I do not know.

Answer 6

We can use

PV=RT

P=RT/V

Answer 7

So Pressure is directly proportional to temperature.

And Inversely proportional to volume.

Answer 8

u know.. i had an accident 2 years ago. i filled the tires on the last summer day of the year, at 13:00 hours....and next day, the car flipped. i was some 1000 meters above from where i filled and temperature was much lower, then the day before

Answer 9

it was a pellety road, and rear tire from left side started to slide

Answer 10

i thought it could be oil.. but i always asked myself, if these facts i mentioned, didn't help to the event

Answer 11

i filled too much 2.7 is a bit too high for my car... but it was summer, and you save some gas, i guessed

Answer 12

yes @hba, but the pressure when u fill the tire is related to external pressure. if i climb in earth, pressure drops. does the pressure inside of the tire raises? or drops? or maintains , and tire expand?

Answer 13

You should have filled more pressure 2.7 bar was not much for the mountains.

Your tire have burst :P

Answer 14

first day of rain, after too many days of summer, its like having residues of soap in a bathtub.. but could these facts have helped to the event?

Answer 15

We can either talk about this theoritically or mathematically.

Answer 16

@rajathsbhat

What would you comment ?

Answer 17

I did not even read most of it :P

Answer 18

i think, as the pressure from the atmosphere drops, the gas inside the tire has less counter force, and can expand..
the pressure inside the tire is always relative due to the one outside.. so i think if, pressure outside drops, the tire tends to expand.
but i dont know the units we are talking about.. like.. if on see level pressure is 1atm, what is the pressure 2000 meters above? is that significant?

Answer 19

Raj would comment better.

Answer 20

i would say that the increase in the tire's pressure because of the drop in atmospheric pressure would have more or less compensated for the decrease in pressure due to the fall in temperature.
So, at the time of the accident, you would have had the same high pressure of 2.7 bar. And everybody knows that you should drop the pressure in your tires significantly when you're trying to climb hills on rugged roads (in order to prevent slipping and rolling).
So ultimately, the high pressure in your tires car caused that extra bounce necessary to flip your car.

Answer 21

Depends,What car are you using ?

Answer 22

it was a skoda octavia 2001

Answer 23

it was a .. how do u call in ur country, tourer? berlina and tourer? a van?

Answer 24

family car?, 5 doors?

Answer 25

Oh then @rajathsbhat is absolutely correct your car flipped.

Answer 26

was it top heavy?

Answer 27

but i wasn't climbing a mountain or something like that.. it was a curve to the left, with a little decline downwards, and the i didn't even started to turn the car, when i felt the rear tire sliding

Answer 28

i just was like 500 meters or something above from where i filled the tyres

Answer 29

see? sliding. that's what happened. And it happened because the pressure in your tires was high.

Answer 30

you are saying decrease of pressure due to fall in temperature.. but what pressure are u talking about? external or internal? both decreases?

Answer 31

internal

Answer 32

if the external. atmospheric, temperature decreases, the tire expands?

Answer 33

2 people in the both front seats, nothing more on the car. 50 km/h.

Answer 34

yeah it would if the rubber wasn't hard. That doesn't mean to say that it doesn't expand at all. It does. But only a bit. Not enough to keep the internal pressure the same.

Answer 35

so external pressure decreases with temperature?

Answer 36

in this place, external pressure on the accident's place was lower then the ones on gas station, first because of less air density, and second because of lower temperature?

Answer 37

External pressure increases with decrease in temp (think of ocean breezes).
But in this case, i would guess that the decrease in external pressure due to the high altitude was much greater than the increase in pressure due to the decrease in temperature. That means that there was an overall decrease in external pressure.

Answer 38

i dont get the ocean breezes..

Answer 39

can you explain

Answer 40

ok you know why you get those cool breezes on a beach in the night?

Answer 41

temperature drops, and the warm air starts to go up, and cold air goes down, making a current

Answer 42

is that it?

Answer 43

Btw, Another thing to take into account is the volume of the tire.. because at this 1 pm on summer day, the tire has a different volume, right?

Answer 44

during the day, the land heats up more than the ocean because water doesn't take heat so well. And this consequently heats up the air above it. In the night, because the air above land is much hotter now, it is at a much lower pressure than the air above the ocean (which is cool). Air move from high pressure areas to low pressure areas. And so, the cool air replaces the hot air resulting in ocean breezes.

Answer 45

ah right

Answer 46

taking into account the volume of the tire leads to complications. In my explanation, i've taken the volume to be constant as long as the tire retains it's basic circular shape (i.e. i assumed that it wasn't flat, which it wasn't.)

Answer 47

so external pressure drops, on the mountain, then the internal pressure increased?

Answer 48

yup

Answer 49

but ur saying the tire's volume stayed equal

Answer 50

more or less.

Answer 51

ah ok, the tire just got harder then

Answer 52

wait a sec. i see what you mean.....

Answer 53

But if the temperature drops, shouldnt the EXTERNAL pressure drops, due to PV=nRT?
And consequently, the pressure inside gets even bigger..

Answer 54

no the atmosphere works in a different way cuz the air can move around a lot. lemme explain...

Answer 55

say it was 40 C outside in your state. That would mean that the air molecules are hot and hot molecules move a lot and bump into each other and move other molecules out of the way. What happens now is that you have fewer air molecules in say a one square meter area than you'd have if the temperature was 20 C when the molecules weren't moving so fast. Lower the number of molecules in a given volume = decrease in pressure. That's why we say mountain peaks have low pressures too (there are fewer air molecules around you and above you)

Answer 56

and these air molecules move from your state to other parts of the world. It's a dynamic system.

Answer 57

i understood that.. but something isnt right then...
your saying that on the summer day with 40C, the pressure in atmosphere is lower, then a day with 20C, at same place? that doesnt make sense. first because of the equation, and second because i know that in the morning, pressure rises with the temperature, as the day starts.

And the molecules in that "bump into each other and moving other molecules out of the way" have to move somewhere else, moving to where pressure is lower , that means going up. AND that means the pressure in the mountains raises, and that means what ur saying is , in hot days, pressure decreases in lower places and increases in higher places.

Answer 58

@rajathsbhat

Answer 59

I did some research and found out that the atmospheric pressure does increase with temperature, but only by a very little amount. This change is not enough to influence major changes in the pressure of car tires. So, I would remove it from my explanation altogether (with this removed, my explanation makes even more sense now (think about why that is)).
Read the third reply here: http://www.newton.dep.anl.gov/askasci/wea00/wea00073.htm

As for the second part, it's not that simple. Atmospheric processes are complicated and influenced by a lot of factors. Again, go though that link to get an idea of why the air cools down as soon as it goes to higher elevations.

Answer 60

I thought this was finished up but happy to see this :)

Answer 61

I wish i can give you more medals for this lol ;P

Answer 62

thanks hba ;) it's the thought that counts ;D

Answer 63

Haha :)

Answer 64

thx man. i will read it carefully