In engineering, what do "smart materials" often change in response to?

Smart materials are a category of materials that have the ability to change their properties or behavior in response to external stimuli. The correct response highlights that smart materials often exhibit changes in reaction to temperature or light. This is because many smart materials are designed to respond to specific physical conditions to enhance functionality in various applications.

For example, thermochromic materials change color when subjected to different temperatures, effectively demonstrating the relationship between temperature and material properties. Similarly, photochromic materials alter their properties in response to light exposure, making them useful in applications such as sunglasses that darken in bright sunlight.

By focusing on temperature and light as triggers for change, we see how smart materials can be utilized in innovative ways across industries, including engineering, healthcare, and consumer products, thereby enhancing their practicality and effectiveness in real-world applications.