Final answer:
The element of art being introduced in the activity described is Texture. This activity would help students visually identify and understand different textures by giving a physical form to something that is usually tactile.
Step-by-step explanation:
In the activity described where second-grade students place thin paper over an object they have found in the classroom and then rub a crayon over the paper on part of the surface of the object, the element of art most effectively introduced to students is Texture. Texture in art refers to the surface quality that can be seen and felt.
By rubbing the crayon over the paper and the object, students can create a visual representation of the textures they explore, whether they're rough, smooth, soft, or hard. The artwork helps students focus on the most important points without overwhelming them and these textures are visually translated onto paper. For instance, a rub over a coin or leaf would show intricate design or vein details respectively. This technique draws students' attention to the critical learning point of introducing them to the element of texture.
Learn more about Texture in Art