Modern physics encompasses complex topics such as relativity, particle properties, atomic structures and quantum mechanics. It usually has prerequisites in calculus and beginning physics courses. Since much of the laboratory work can be performed by computer, online modern physics classes are usually taken entirely outside the classroom. Online physics classes usually fall under either classical physics or modern physics. Some online physics classes have regular assignments with specific due dates, while others may be more flexible in nature. Online classes can be conducted in several ways, including streaming video and course delivery systems such as Blackboard. Some classes may require on-campus lab work.