A physical characteristic is any measurable property that is involved in the physical system and intensity on the objects state and behavior. Physical characteristics can be qualitative, such as shininess or brittleness, or quantitative, such as mass or temperature. Measurable physical quantities are often referred to as observables. Physical properties are traditionally defined by classical mechanics and are often called mechanical properties. Other broad categories of physical properties include electrical properties, optical properties, thermal properties, etc. . Examples of physical characteristics in humans include hair color, eye shape, and complexion. In geography, physical characteristics refer to natural features on Earth, such as landforms. Physical characteristics can play a role in defining how people are viewed by others, especially in terms of forming first impressions.