Final answer:
The relationship between volume and temperature at constant pressure is a direct one, where volume increases with temperature as described by Charles's Law.
Step-by-step explanation:
The relationship between volume and temperature when pressure is constant is a direct one. This means that as the temperature of a gas increases, its volume also increases if the pressure of the gas remains unchanged. This relationship is known as Charles's Law, which states that the volume of a fixed amount of gas maintained at a constant pressure is directly proportional to its temperature in kelvins.
At constant temperature, by contrast, the volume and pressure of the gas are inversely proportional to each other. This is a separate principle, called Boyle's Law, and not the focus of this particular question. Understanding the relationship between volume, temperature, and pressure is fundamental in the study of gases in physics and chemistry.