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# Force of friction keeping the block stationary

Investigate the forces at play when a block of wood on a wedge is stationary. Understand the role of friction and the normal force in balancing the force of gravity. Learn how to calculate the coefficient of static friction and its implications in real-world scenarios.
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Created by Sal Khan.

## Want to join the conversation?

• Where is the first video that this video refers to?
• It's actually the next video in this section!
I think they are just out of order on accident :)
• Hello,
At around , the video indicates that static friction is 49/(50 * 3^.5) = 0.72. However, this value calculates to ~ 0.59. Regards.
• This video refers to a previous video, where is it..:)
• Curious as to why 1 N was arbitrarily put down to set the block into motion. How do we know that 1 N will actually move the block?? Could we have just guessed 2.. ? The coefficient of static friction is a constant so I'm just slightly confused.
(1 vote)
• I believe he was just using that number randomly for this example. It doesn't have any real significance. He mentioned that in this scenario we found that value experimentally. It allowed us to figure out the "budging" force, as he calls it. It could have been any value really. He just needed a number for the example. This example just shows how the coefficient of static friction relates to the "budging" force and the normal force.
The coefficient of static friction is a constant, but remember this constant is different for different materials.

Hope this helps.