In a convection current, as the temperature of a fluid increases, its density ______.

In a convection current, as the temperature of a fluid increases, its density ______.

• A. It decreases
• B. It increases
• C. It stays the same
• D. It is unpredictable

Answer: (A)

When a fluid is heated, its particles gain energy and spread out, causing the substance to expand. With the same amount of mass now occupying a larger volume, density (mass per unit volume) drops. In a gravitational field, this less dense, warmer fluid becomes buoyant compared to the cooler surrounding fluid, so it rises. As it rises and cools, it becomes denser again and sinks, setting up the circulating pattern of a convection current. So, as temperature increases, density decreases. This inverse relationship between temperature and density under normal conditions explains why warm fluids rise and cool fluids fall in convection. (Note: there are a few exceptions, like water near 4°C, but the general behavior is density decreases with increasing temperature.)

When a fluid is heated, its particles gain energy and spread out, causing the substance to expand. With the same amount of mass now occupying a larger volume, density (mass per unit volume) drops. In a gravitational field, this less dense, warmer fluid becomes buoyant compared to the cooler surrounding fluid, so it rises. As it rises and cools, it becomes denser again and sinks, setting up the circulating pattern of a convection current. So, as temperature increases, density decreases. This inverse relationship between temperature and density under normal conditions explains why warm fluids rise and cool fluids fall in convection. (Note: there are a few exceptions, like water near 4°C, but the general behavior is density decreases with increasing temperature.)