Gas and Water: In Equal Measure

gallon of gasGas and Water:  In Equal Measure

Almost anyone who has had a high school science class has been hit with the trick question: “Which weighs more? A pound of bricks, or a pound of feathers?” Which is a fairly obvious conclusion if you listen to the question. They both weigh the same as it’s measured by weight. However, if you change the question to Which weighs more, a gallon of water or a gallon of gasoline, the answer gets a bit trickier. While a gallon of gasoline weighs 6.2 lbs, a gallon of water weighs heavier at 8.33 lbs. Why is there such a difference between the two?

Wording is Key

Go back to the bricks and feathers for a moment. We know that they weigh the same because we’re using the pound as our standard metric. When it comes to weight, it translates equally despite whatever it is we happen to be comparing. When it comes to measuring water and gas on the other hand, we’re using gallons. A gallon is only specifying the volume and not the actual weight. So while a gallon of water and a gallon of gasoline can occupy the same amount of space, they can and will weigh differently.

Why is Water Heavier?

Ignoring the possibility for sediment, dissolved solids and other particulate matter (whether it be minerals in the water or impurities in the gasoline) a gallon of water has over two pounds vs the weight of a gallon of gas. This is because the molecules that make up water are denser than that of a gasoline molecule. Because of the difference in density, it’s easy to imagine more water being crammed into that same sized container than that of gasoline. Another way to look at it is that gasoline molecules take up more space than water, which is why, even though they both share the same volume, they don’t weigh the same.

Why Does it Matter?

Actually, in our modern world, weight matters quite a bit. Imagine two tanker trucks together. One filled with water and the other gas. Despite holding the same volume of liquid, the truck filled with gasoline is significantly lighter than the truck filled with water. This can make all the difference in the world when it comes to matters such as toll by weight, or more importantly, the weight limit of a bridge. Understanding the difference in weight can make help keep deliveries from turning towards disaster.

Weight plays a very important role in our lives, and not just involving gasoline and water. Scales are used more often than you’d expect in a wide variety of places, from the highway to the grocery store. Having these scales properly maintained and calibrated is what keeps everything in check. Whether it be getting a fair price for asparagus, or, more topically, getting what you pay for at the pump. Garber Metrology has been servicing the mid-Atlantic regions need for scales and weight calibrations for close to 40 years. Their specialists understand, pound for pound, how important it is to be accurate, especially when it comes to measuring weight.