When you’re driving, it’s important to keep your car in the same air pressure as when you were born. This is called “the law of atmospheric pressure.” The atmospheric pressure is what’s inside your car. It’s about 14.7 pounds per square inch (psi). The atmospheric pressure outside your car is about 0.79 psi. That means if you have a car with an air conditioning system that uses a compressor to turn water into ice, the compressor will work at 0.79 psi and the water will be at 0.14 psi (14.7/0.79 = .14). If you don’t have an air conditioning system, your car will have a negative pressure inside and outside of it, which is called “the vacuum.” The negative pressure inside your car is about 14.7/0.79 = -5 psi or -14 Pa or 14 pounds per square inch (psi). The negative pressure outside your car is about 0.79/0.14 = -3 psi or -3 Pa or 3 pounds per square inch (psi).
