In a vacuum, light moves at its maximum speed of approximately 299,792 kilometers per second (km/s). In air, it slows slightly to 299,700 km/s. When light passes through denser substances, its speed decreases further. In water, it travels at about 225,000 km/s, while in glass, it slows to around 197,000-200,000 km/s. The speed drops even more in diamond, moving at roughly 124,000 km/s due to the material's high density. 0 reply
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