glass is a kind of object & breaking down an object changes that object 's shape ->  breaking a glass changes the shape of the glass  breaking a glass changes the shape of the glass & shape is a kind of physical property ->  breaking a glass changes the physical property of the glass  breaking a glass changes the physical property of the glass & if something undergoes a physical change then the physical properties of that something will change -> breaking a glass is an example of a glass undergoing a physical change