According to NASA, a robot functions by emulating physical characteristics of human beings such as the body structure, muscle system, sensory system, power source and brain system. Most robots are reprogrammable, which means their behavior can be changed by writing a new program to its computer.
Although the designs of robots vary, one thing they all have in common is a movable body. Robots move using motorized wheels or dozens of movable segments made of plastic or metal. The individual segments are similar to the bones in the body because they are also connected to joints on the robot's main body. Actuators such as electronic motors and solenoids are used to spin wheels and pivot jointed segments. Some robots also use a hydraulic system or pneumatic system powered by a battery or electrical outlets in a wall. Although some robots have sensory systems, most are unable to see, hear, smell or taste. However, robots have a sense of movement that gives them the ability to monitor their own motion. Robots can also mimic specific body parts, such as robotic arms used by NASA to move large objects in space. They are also used as spacecrafts that explore other worlds or as unmanned aircraft.