00:01
Tony decides it's time to upgrade his lamp on his desk from an ancient lamp to a ring light.
00:09
So there's his desk.
00:11
We'll just pretend this is his lamp.
00:15
And he's pushing it along.
00:20
And eventually it's going to fall off and into his bin, right? so we're giving the coefficients of friction.
00:31
So static coefficient 0 .54.
00:37
Kinetic or dynamic coefficient is 0 .42.
00:44
So what is the magnitude of the force tony must exert to move the lamp? call the force he exerts f.
00:54
Let's draw a free body diagram here.
00:57
The lamp.
00:59
So he's exerting a force capital f.
01:03
Friction exerts a force lowercase f.
01:07
The lamp has a weight, w.
01:11
Which they tell us is 150 newtons and then upward we have a normal force right from the table so what magnitude needs to our magnitude of forces needed to move the lamp so right before the lamp starts to move the sum of the forces in the x equals zero right so x y and what we want to do is find the situation where this is true, but any additional force would make this not true.
02:00
So what forces do we have? capital f minus friction equal zero.
02:09
The frictional force for static friction is less than or equal to the static coefficient times the normal force.
02:21
So what does that mean? why? less than.
02:24
Well, if you have the lamp sitting there and you push on it with the tiniest of forces, right? well, friction's going to push back with that same tiny force.
02:37
Say you increase it a little bit.
02:38
Friction will push back with the exact same force up into a point, right? there's a point at which if you push, say, i'll just pick a random number, if you push 100 newtons of force, the lamp doesn't move, but when you push 101, now the lamp starts to move, right? and that's because at some point you overcome static friction...