“The teen playing tennis in Figure below is having fun. The other teen in the same figure is working hard studying for an exam. You can tell by their faces which teen is doing work — or can you? Would it surprise you to learn that the teen who is working is the one who is having fun playing tennis, while the teen who is studying isn’t doing any work at all? The reason why has to do with how work is defined in physics.” Ck – 12 (Chapter 16.1)
Well, It’s amazed me as much as it does to you. According to Google, work means an activity involving mental or physical effort done in order to achieve a purpose or result. However, In physic, according to Ck-12 Work means, work means the use of force to move an object. So the girl in the picture a is working and girl in picture b is not working because she does not apply any force. ( in physic)