Why do you use water displacement and not a ruler to determine the volume of pennies?

Water displacement is used to determine the volume of pennies because it accurately measures the volume of irregularly shaped objects, like coins, which can be difficult to measure with a ruler. This method accounts for the actual space the pennies occupy when submerged in water, providing a precise volume measurement. Additionally, using a ruler may not capture the nuances of the coins' shapes or any variations in size, while displacement gives a direct measurement based on the volume of water displaced.