Tire-pressure gauges

The reading on a tire-pressure gauge is 35 psi. What is the equivalent pressure in kilopascals ... 

A tire-pressure gauge is a device that measures the pressure of the air inside an inflated tire or a basketball. Because an iminflated tire contains some air at atmospheric pressure, a tire-pressure gauge records the amoimt that the tire pressure exceeds atmospheric pressure. 

Explain whether a tire-pressure gauge should be recalibrated for use at locations where atmospheric pressure is less than that at sea level. 

Compare and contrast how a barometer and a tire-pressure gauge measure gas pressure. 

Fahrenheit or Celsius degrees), fever thermometer (Fahrenheit or Celsius degrees), kitchen measuring spoons (tablespoons, or teaspoons), automobile speedometer (miles per hour or kilometers per hour), directional compass (degrees), tire pressure gauge (pounds per square inch), protractor (degrees). 

Quick-fix stuff. A bungee cord, duct and electrical tape, pliers, socket and screwdriver sets, a tire pressure gauge, and jumper cables can all get you out of a tight spot in a hurry. 

Various microdevices, that is, MEMS products, have also found applications in various consumer products, that is, sport shoes with automatic cushioning control, digital tire pressure gauges, smart toys, washers with water-level controls, and so on. 

As the temperature of a sample of fixed volume increases, the pressure increases. If the external pressure acting on a gas sample contained in a piston assembly is increased, the volume will diminish. These are statements of observed phenomena, and they are consistent with our everyday experience. For instance, an automobile tire that has reached a higher than ambient temperature gives a higher reading on a tire pressure gauge than it would at the ambient temperature. Or, a small balloon that can fit between our hands can be diminished in size by squeezing. Experiments can establish mathematical relationships that quantify these observations. 

What is more important to us is the differential pressure inside the tire compared to outside the tire (atmospheric pressure). For reasons such as these, the world has adopted a second and artificial zero, at atmospheric pressure as a reference point. This is why a simple pressure gauge will read zero at atmospheric pressure. 

When we measure the pressure of air in a tire by using a pressure gauge, we are actually measuring the gauge pressure, the difference between the pressure inside the tire and the atmospheric pressure. A flat tire registers a gauge pressure of 0, because the pressure inside the tire is the same as the pressure of the atmosphere. 

Vacuum and pressure measurements were all originally made compared to atmospheric pressure, or gauge pressure. The term psig (pounds per square inch-gauge) refers to this comparison. Absolute pressure includes atmospheric pressure (14.7 psi) and is called psia (pounds per square inch-absolute). For example, your tire pressure is 35 psig or 49.7 psia. Generally, unless otherwise identified, the lone identification psi refers to gauge pressure. 

Before leaving on a trip to Florida, you measure the pressure inside the tires of your car at a gas station. At -7.5°C the tire pressure is found to be 206.5 kPa. When you arrive in Florida, you stop for dinner. Before leaving, you once again measure the tire pressure at a gas station beside the restaurant. Most pressure gauges in the United States are calibrated in psi. You find the tire pressure to be 34.3 psi. What is the approximate temperature in Florida (Hint See the MathLink on page 428 to find out how to convert psi to kPa.)... 

Most pressure gauges give readings wliich are tire difference between the pressure of interest and tiie pressure of tire surrounding atmosphere. These readings are known as gauge pressures, and can be converted to absolute pressures by addition of tire barometric pressure. Absolute pressures must be used in tliennodynamic calculations. 

The gauge pressure in a tire is 28 psi, which adds to atmospheric pressure of 14.0 psi. What is the internal tire pressure in kPa ... 

Before a trip from New York to Boston, the pressure in an automobile tire is 1.8 atm at 293 K. At the end of the trip, the pressure gauge reads 1.9 atm. What is the new Celsius temperature of the air inside the tire (Assume tires with constant volume.)... 

A small, hand-held pressure gauge can be used to monitor tire pressure. 

A bicycle tire is inflated to a gauge pressure of 30.0 psi at a temperature of t = 0°C. What will its gauge pressure be at 32°C if the tire is considered nonexpandable (Note The gauge pressure is the difference between the tire pressure and atmospheric pressure, 14.7 psi.)... 

Unfortunately, the barometer can measure only atmospheric pressure. It cannot measure the air pressure inside a bicycle tire or in an oxygen tank. You need a device that can be attached to the tire or tank. This pressure gauge must make some regular, observable response to pressure changes. If you have ever measured the pressure of an inflated bicycle tire, you re already familiar with such a device. 

The most familiar tire gauge is about the size and shape of a ballpoint pen. It is a convenient way to check tire pressure for proper inflation regularly. Proper inflation ensures tire maintenance and safety. 

When you measure tire pressure, you are measuring pressure above atmospheric pressure. The recommended tire inflation pressures listed by manufacturers are gauge pressures that is, pressures read from a gauge. A barometer measures absolute pressure that is, the total pressures exerted by all gases, including the atmosphere. To determine the absolute pressure of an inflated tire, you must add the barometric pressure to the gauge pressure. 

You use a pressure gauge to measure the air pressure in your bicycle tires on a cold morning when the temperature is — 5°C. The gauge reads 53 psi. The next afternoon, the temperature has warmed up to 11°C. If you measure the pressure in your tires again, what would you expect the reading on the pressure gauge to be Assume the volume of air in the tires is constant. 

Although the pressure at sea level is 14.7 psi, pressure gauges are calibrated to read 0 at 1 atmospheric pressure. Therefore, when one measures pressure in an automobile tire, say 32 psig, one is measuring the pressure above atmospheric. In this example, the total pressure (also called the absolute pressure) in the tire is actually 46.7 psia because the pressure at sea level is 14.7 psia. In order to distinguish between gauge (g) and absolute (a) pressure, the respective letter is appended to the psi designation. 

Most pressure gauges show the magnitude of the pressure of a or a liquid relative to the local atmospheric pressure. For example, when a tire pressure gai shows 32 psi, this means the pressure of air inside the tire is 32 psi above the local atmospheric pressure. In general, we can express the relationship between the absolute and the gauge pressure by... 

On a cold, f = —3°F, late winter day in Kazakhstan, Cyril Bond checks the pressure in the front left tire on his Aston Martin-Hyundai Accent (special edition) service car and finds that it reads only 17 pounds per square inch, psi. After consulting with Nurudin, a garage attendant, Cyril asks him to add more air, until the pressure gauge reads 2.3 kg/cm, or atmosphere," atm (Nurudin is using a metric pressure gauge). 

Common pencHype pressure gauges actually measure the dHfererKe between irrtemal and external pressure. Thus, if the tire is completely flat, the reading of 0 psi means that the pressure msxte the tire is the same as that outsidb the tire. 

One of the properties of gases discussed above is that of gas pressure. Gas pressure is something that is routinely measured in everyday life. For example, when you pump your bicycle tire or your automobile tire full of air, it is desirable to measure the pressure of the air inside the tire with a pressure gauge to determine whether you have added the correct amount of air. Also, when meteorologists measure barometric pressure, they measure the pressure exerted by the air in the vicinity of the weather station. Barometric pressure changes with changing weather conditions, so its measurement is often used to predict weather. 

The U.S. equivalent of 1 atm is 14.7 Ib/in. (psi). When you use a pressure gauge to check the air pressure in the tires of a car, it may read 30-35 psi. This measurement is actually 30-35 psi above the pressure that the atmosphere exerts on the outside of the tire. Table 11.2 summarizes the various units used in the measurement of pressure. 

Calculate the number of moles of gas in a 3.24 L basketball inflated to a total pressure of 24.3 psi at 25 °C. (Note The total pressure is not the same as the pressure read on a pressure gauge such as the type used for checking a car or bicycle tire. That pressure, called the gauge pressure, is the difference between the total pressure and atmospheric pressure. In this case, if atmospheric pressure is 14.7 psi, the gauge pressure would be 9.6 psi. However, for calculations involving the ideal gas law, you must use the total pressure of 24.3 psi.)... 

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