What is the statement that limits the lengths of links in a planar four-bar linkage for continuous relative rotation?

• A. Grubler's Law
• B. Coriolli's Law
• C. Grashof's Law
• D. Freudentein's Law

Answer: (C)

The correct answer is Grashof's Law, which addresses the conditions under which a planar four-bar linkage can achieve continuous relative rotation. According to Grashof's Law, a four-bar linkage consists of four links: a fixed frame (ground link) and three moving links. The law states that for a four-bar linkage to allow continuous rotation between at least one pair of links, the sum of the shortest link and the longest link must be less than or equal to the sum of the other two links.

This condition ensures that one of the moving links can continuously rotate with respect to the fixed link without locking up or stopping rotation, which is essential for many mechanical applications. When the lengths are appropriately defined in accordance with Grashof's Law, the mechanism can operate smoothly and effectively, facilitating tasks such as lifting or moving components in machinery.

The other options represent different principles that do not specifically address the conditions for continuous relative rotation in four-bar linkages. Thus, Grashof's Law is fundamental for understanding and designing such mechanical systems where continuous motion is required.