Energy-Mass Equivalence Keychain

Featuring the iconic equation and related charms, this piece is sure to resonate with those who appreciate it! We aim to create items that convey a sense of understanding, even to those unfamiliar with the concepts. This is the famous equation from Einstein's theory of relativity. It's also popular among fans of Dr.STONE. In honor of the "Twin Paradox" (where one twin stays on Earth and the other travels through space), which is often mentioned when explaining the theory of relativity, we've included a rocket charm. --- ☆ Materials Plastic Resin Metal (Please be mindful of potential allergies) ☆ Size The size of the equation charm varies by type. Each piece is handmade, so there may be individual differences even for the same equation. Please choose your favorite. --- This item uses resin. While it is resistant to yellowing from UV exposure and the passage of time, please store it away from direct sunlight after use. ※ As metal parts are used, those with allergies or concerns are kindly asked to refrain from purchasing. ※ As this is a handmade item, there may be slight variations in size and shape for each piece. Your understanding is appreciated. ※ If natural materials are used for parts, there will be individual differences in size, shape, color, and pattern.