In an article on tire maintenance, it is stated that tires lose air over time, and pressure losses as high as 90 kpa (13psi) per year are measured. the article recommends checking tire pressure at least once a month to avoid low tire pressure that hurts fuel efficiency and causes uneven thread wear on tires. taking the beginning tire pressure to be 220 kpa (gage) and the atmospheric pressure to be 100 kpa, determine the fraction of air that can be lost from a tire per year.

0.28125

Explanation:

Given:

Loss in the tire pressure = 90 kPa

Gage pressure = 220 kPa

Atmospheric pressure = 100 kPa

Now,

the absolute pressure is given as:

on substituting the values, we get

the initial absolute pressure of the tire as, P₁:  220 + 100 = 320 kPa

also, we know

P×V = nRT

where,

V represents the volume of air in the tire

n is the number of moles of gas in the tire

R is the gas constant

and, T represents temperature

now, the volume and temperature for both cases remains the same

thus, for the initial pressure, we have

P₁V = n₁RT

or

320 × V = n₁RT

now for case 2 we have

P₂ = 320 kPa - 90 kPa = 230 kPa

thus,

P₂V = n₂RT

or

230 × V = n₂RT

now, by dividing 1 by 2, we get

or

thus,

fraction of air lost is 1 - 0.71875 = 0.28125

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia

3. dark matter

empty space could also be a simple vacuum