Grace Brown leads a busy school life. Apart from the many required subjects, the 14-year-old girl also sings in a choir (合唱团) and plays the piano. The school day lasts from 8 a.m. to 4 p.m., but Grace has so many activities to attend that she has no time for P. E.classes. That’s why Grace has chosen to take P. E. classes on her own time.

Her school has allowed her to try “virtual” P. E.. For many subjects, tests and textbooks have become available on computers. Now, new technologies are also having an effect on P. E.. Grace wears a fitness tracker(追踪设备) called Fitbit on her arm while exercising. She usually exercises three times a week for 30 minutes each time. A program on her computer records her activity. Grace needs to hand in the records to her school every week.

“Virtual” P. E. is becoming more and more popular among teenagers. Usually, P. E. teachers don’t guide their Fitbit-wearing students in real time. But they do lead the students’ work by setting goals. The students can choose their favorite activities. Those who swim or dance all year round may easily meet the workout requirements. As for Grace, she has added light running and cycling to her days. Some schools, however, do not support this trend. “Physical activity is different from physical education,” said a P. E. teacher. “Physical activity is great for the body. Everybody is moving. But in P. E. classes, students are taught not only how to move but also things like teamwork.

Have you wondered how your pets are feeling? When your dog wags (来回摇摆) its tail, does that mean it is happy? A new app called Happy Pets can tell you what’s going on.

The app uses artificial intelligence (AI) to analyze (分析) the facial(面部的) expressions of cats and dogs. Then it can tell you what kind your pet is and how it is feeling. It can show the five most common feelings — happiness, anger, neutral (中性的) feelings, sadness and fear.

Researchers at the University of Melbourne in Australia developed the app. The key technology used in the app is facial recognition, a common use of AI. We can unlock our mobile phones or enter train stations with facial recognition readers. But this is the first time that the technology has been used for animals.

The app’s AI was first taught to recognize a picture of an animal. Then, it was taught to recognize the facial features of cats and dogs. Next came the most important step — teaching it to detect (察觉) emotions (情感) according to certain facial features. For instance, if a dog closes its eyes and mouth while changing the position of its ears, this means the dog is scared. To master this skill, the AI program “saw” and “read” thousands of example images.

Are the results correct? The researchers think they are believable since the app has been tested many times. Interestingly, they have found that cats are harder to read than dogs. In the future, the app might also be able to analyze a pet’s body to make its readings more correct.