Toys with an end mass greater than 0.02 kg (0.04 lb) shall have cord length less than 50 cm (20 in. ) measured when rotating at 80 r/min.

末端质量大于0.02公斤（0.04磅）的玩具上的绳在以80转每分钟的速度旋转时长度应小于50厘米（20英寸）。

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Wind tunnel measurement gives the velocity field and vorticity field in intersection plane at different downstream position, which is up to 20 times cord-length.

风洞实验采用PIV测量了沿流向下游不同截面的涡量场和速度场，测量截面距机翼后缘最远达到20倍弦长。

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So, go ahead and get the first-grader a Firefly if you must (we prefer two tin cans and a very long length of cord).

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The coiled cord is tangle-resistant and easier to manage, while the length permits users to handle their device anywhere in the car while still charging.

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Compatible with most USB chargers, the coiled cord is tangle-resistant and easier to manage, while the 6 ft. cable length provides better mobility while in use.

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