这就是著名的靠，摩擦力平衡的例子，现在我想讨论一个，可以在重力作用下，自由摆动的悬挂物体。
So you saw in a striking example of where friction helped us to balance, and now I want to discuss an object that is hanging and that can freely swing due to gravity.
我的床还会摇摆。它简直就是一块加了床垫的平放著的秋千架，我在睡觉的时候还可以不停摆动。
It's a laying-swinging patio bench with a mattress on top so that I can rock when I sleep. I love swings and swing every night for an hour in my backyard on our swing set.
我的床还会摇摆。它简直就是一块加了床垫的平放著的秋千架，我在睡觉的时候还可以不停摆动。
It's a laying-swinging patio bench with a mattress on top so that I can rock when I sleep. I love swings and swing every night for an hour in my backyard on our swing set.
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