This lecture covers measurement methods for elastic properties, including the elastic modulus and Poisson's ratio. It discusses the behavior of different materials under stress, such as ceramics, metals, and polymers. The lecture also explores the concept of elastic deformation in elastomers and the measurement of elastic properties using ultrasound. Additionally, it delves into the relationship between elastic constants and the anisotropy of materials. Material selection criteria based on elastic properties and density are presented, along with the use of Ashby maps for material selection. The lecture concludes with a discussion on specific stiffness indices and the performance of materials in various applications.