# Gauge Pressure (teacher completely skip this)

• BunDa4Th
In summary, the problem is asking to find the new gauge pressure in a tire after the temperature drops from 25*C to -10*C, given the initial gauge pressure of 4.86x10^4 Pa. The correct approach is to use the gas law equation Pa_i/T_i = Pa_f/T_f, where T_i and T_f are the initial and final temperatures in Kelvin. However, in order to find the absolute pressure, which is needed in the equation, the atmospheric pressure (1.01x10^5 Pa) must be added to the gauge pressure. Therefore, the absolute pressure in the tire after the temperature drop is 4.86x10^4 + 1.01x10^5 Pa
BunDa4Th

## Homework Statement

A tire contains air at a gauge pressure of 4.86x10^4 Pa at a temperature of 25*C. After nightfall the temperature drops to -10*C. Find the new gauge pressure in the tire. Pa

## Homework Equations

Pa_i/T_i = Pa_f/T_f
T = T_c + 273

## The Attempt at a Solution

4.86x10^4/298 = Pa_f/263

Pa_f = 4.29x10^4

This is incorrect. I read the book and it said something about absolute pressure - atomospheric pressure (1.01x10^5). The problem i have is how do i find the absolute pressure? Also am i going into the right approach on solving the problem?

or

Am i completely off on what I am doing. Mainly i need help on figuring out how to get the absolute pressure.

Gauge pressure is the pressure difference above atmospheric pressure. For example if you fitted a new car tyre and didn't inflate it, the gauge pressure (as measured by most pressure gauges - hence the name) would be zero. But the absolute pressure inside the tire isn't zero, it is the same as atmospheric pressure.

In your gas law equation you need absolute pressure and absolute temperature. You used abs. temperature correctly.

Use the standard value for atmospheric pressure to convert gauge pressure to absolute.

Raymond Reddington
The gauges at a fuel station reads "gauge pressure". That is the gauge reads zero pressure if a tire is completely deflated. The guages therefore reads only pressure above the local atmospheric pressure. To get the absolute pressure one only need to add the atmospheric pressure to the gauge pressure (hope it make sense).

if i understand this correctly the absolute pressure is

4.86x10^4 + 1.01x10^5

That is correct.

## 1. What is gauge pressure?

Gauge pressure is the measurement of pressure relative to atmospheric pressure. It represents the difference between the pressure being measured and the surrounding atmospheric pressure.

## 2. How is gauge pressure measured?

Gauge pressure is typically measured using a pressure gauge, which contains a sealed chamber with a known pressure and a mechanism to indicate the difference in pressure between the chamber and the surrounding area.

## 3. What is the difference between gauge pressure and absolute pressure?

Gauge pressure is measured relative to atmospheric pressure, while absolute pressure is measured relative to a perfect vacuum. Absolute pressure will always be higher than gauge pressure, as there is no pressure in a perfect vacuum.

## 4. Why is gauge pressure important in scientific measurements?

Gauge pressure is important in scientific measurements because it allows for accurate and consistent readings, as it accounts for the air pressure variations in the surrounding environment. It is also used in many industrial and engineering applications to measure pressure differentials.

## 5. How can gauge pressure be converted to absolute pressure?

To convert gauge pressure to absolute pressure, you simply add the atmospheric pressure to the gauge pressure reading. This will give you the total pressure, including the pressure of the atmosphere.

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