The sand at a sandy beach on a sunny summer day would feel warmer than the water. This is because of the different thermal properties of sand and water, particularly the specific heat capacity. Water has a very high specific heat capacity, about 4.184 J/(g·K), which means it requires a lot of energy to increase its temperature. This is due to hydrogen bonding between water molecules that allows water to store a large amount of heat without a significant rise in temperature. On the other hand, sand has a much lower specific heat capacity, so it heats up more quickly with the same amount of sunlight energy. Additionally, water conducts heat more slowly and also has a higher heat capacity, so it warms up more gradually and remains cooler to the touch compared to sand, which heats quickly but also cools faster. The sun's rays only heat the very surface of the sand, but they penetrate deeper into the water, distributing the heat over a larger volume. In summary, the sand feels warmer because it heats up faster than water due to its lower specific heat capacity, while water heats more slowly because its high specific heat capacity requires more energy to raise its temperature significantly. This difference explains why sand feels hot and water feels cool on a sunny summer day at the beach.