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# Static and kinetic friction example

Explore how different kinds of friction impact acceleration with the example of a block of wood on some dirt. Determine the acceleration of the block when pushed with a force of 100 N, taking into account the coefficients of static and kinetic friction. Created by Sal Khan.

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• In this video, you show the static and kinetic coefficient. I'm having trouble figuring out how to find those. Have I somehow missed a video that shows you how to find them? • Sal says he calls it the "budging force".... what is it generally called? • How does the duration of the force being applied affect the acceleration? Also, why isn't the duration of the application of force normally supplied in Physics videos? It just occurred to me that it might be rather important. I assume that the duration time would have to be measured only to a certain extent. Can you help me with this? • If the force is only applied once and not constantly, does the static friction affect the object's acceleration throughout its entire motion? • when we ride a nail into a wooden chunk and upturn it it doesnt fall down. though we know it is the friction bw the nail and thye chunk where does the normal reaction force act to produce that much friction. • Could someone please explain what the budging force is? How can I understand this in practical terms? And how is it different from the normal force? • Budging force is the force needed to get the block to overcome static friction and start moving as described at around . Friction while you're moving (kinetic friction) is different from friction that you need to overcome so you can start moving (static friction). In practical terms, if you were on a sled, in order to start sliding, you may need a push from behind so you could overcome the static friction between the sled and the snow.

Don't confuse any of this with normal force. Normal force is an opposing force to gravity exerted in the upward direction by the ground. It's from Newton's 3rd law, which in simple terms says "every action has an equal and opposite reaction." The normal force is also always at a right angle. In fact, in physics and math we often the word "normal" to describe anything that's at a right angle with something else. So if you see the word "normal" in a physics problem, it's referring to something that's perpendicular to something else.
• Could someone give me some examples of static friction? I'm still a little bit confused about about it.
Thanks! • Static friction is the force of friction on an object that is not moving. If you push on a stationary block and it doesn't move, it is being held by static friction which is equal and opposite to your push. Once your push exceeds the maximum possible static friction (budging force = μN), then the block will start moving. The moving block will then experience kinetic friction which is smaller than the static friction.
• At , the larger the normal force the larger force to cause the body to move and the larger force of friction. But isn't it also means that the larger the normal force, the smaller the coefficient of friction because Normal force is inversely proportional (Fb/Fn= μ) and the smaller coefficient of friction means harder to move?   