来自《耶鲁大学开放课程：基础物理 第4集 第4集》
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not always, this is always true,这并不总是一直是对的 -
but in our example you may replace it by μs · m · g,但在这里可以用 μs·m·g 来表示摩擦力 -
because N = m · g.因为 N = m·g -
So the force of friction seems to depend on所以摩擦力看起来取决于 -
how heavy the object is that's sitting on the table.桌子上的物体有多重 -
But what does it not depend on that it could depend on?但什么是它可能取决于但是并未取决于的因素呢 -
Can you think of something else it could depend on but doesn't?你们能不能想出这样的因素呢 -
Yes?说吧 -
It doesn't depend on the area of contact.它并不取决于接触的面积 -
In other words,换句话说 -
if this was a rectangular block,如果这是一个矩形块的话 -
it doesn't seem to matter whether it's doing that它这样放置还是这样放置