Which factor most directly influences a substance's temperature?

The amount of heat added to a substance is the primary factor that directly influences its temperature. Temperature is a measure of the average kinetic energy of the molecules within a substance; as heat is transferred to the substance, the energy of its molecules increases, causing them to move more vigorously. This increase in molecular motion leads to a rise in temperature.

Heat is essentially energy in transit, and when it is absorbed by a substance, it results in a corresponding increase in its thermal energy, thereby elevating the temperature of that substance. Other factors like density, color, and environmental pressure can have secondary effects on temperature under specific conditions, but they do not directly change the temperature in the same way that the addition of heat does. For instance, while darker colors absorb more heat and may increase temperature indirectly, it is not the color itself that alters the temperature, but rather how it influences heat absorption.

Similarly, density and pressure can affect how heat is distributed in a substance or how much heat it can hold, but the direct effect of temperature change occurs with the input of heat. Thus, the most direct influence on temperature is the amount of heat added.