Dogs act like toddlers when you need help - but cats just watch. Scientists compared 3 groups: pet dogs, cats, and human toddlers in an experiment where a human parent hides and pretends to look for an object. 75% of dogs and children helped. Cats only helped if it was in their personal interest.

2026年1月14日 · 郭瑞 · 来源：tutorial资讯

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Leonardo da Vinci is usually credited with conducting the first systematic study of friction in the late 15th century, a subfield now known as tribology that deals with the dynamics of interacting surfaces in relative motion. Da Vinci's notebooks depict how he pulled rows of blocks using weights and pulleys, an approach that is still used in frictional studies today, as well as examining the friction produced in screw threads, wheels, and axles. The authors of this latest paper used an experimental setup similar to da Vinci's.