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Cornell University

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Kai Chen

(I) What is the magnitude of the momentum of a 28-g sparrow flying with a speed of 8.4 m/s?

07:43

Kathleen Tatem

(II) A person has a reasonable chance of surviving an automobile crash if the deceleration is no more than 30 $g$'s. Calculate the force on a 65-kg person accelerating at this rate.What distance is traveled if brought to rest at this rate from 95 km/h?

04:39

Muhammed Shafi

(I) A 7150-kg railroad car travels alone on a level frictionless track with a constant speed of 15.0 m/s. A 3350-kg load, initially at rest, is dropped onto the car. What will be the car's new speed?

04:27

(I) A 110-kg tackler moving at 2.5 ms meets head-on (and holds on to) an 82-kg halfback moving at 5.0 m/s. What will be their mutual speed immediately after the collision?

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In this video, we introduced the concept of electric field lines. This helps us visualize what an electric field actually looks like. So let's consider this blue particle here with charge positive capital que At a point right here. We know the electric field points in this direction, and if we move a little bit further away, who points in that direction? If we lose along that line, well, we know for a point charge, the electric field radiates outward, so point charges a very simple example. If we have a quaint here, the field will always point outward and similarly over here and over here. And the direction, of course, is away from a positive charge. So let's draw on some more. I know it's a little tedious to draw it all out, but it does tell us something when we do so. One thing we'll notice is where do these field lines become most dense? Well, we know it's in this area closest toe our point charge Now recall the electric field for a point charge has that formula. Let's use capital Q. To match our charge here, so we know its strongest. The closer we are to our point charge. And that's one thing that the electric killed helps demonstrate. Fields are a lot less dense out here. The less dense the field lines are, the weaker. The electric field is around those around that area. So right away we can see the electric field lines. Let us see how strong the electric field is at any point in space. Of course, this was a very simple example, slightly more complex. It's an electric dipole. So let's start with the easy, easiest region, the one right between these two charges of these two particles, all opposite charge. Well, we know that the electric field lines or the electric field points away from a positive charge and toward a negative charge. And really, what it's telling us is, at each point, we just calculate the electric field. Now this isn't to confuse us and say that these lines are the electric field. They are not what they are or what they do it. Show us which way the electric field points. Any tangent to a field line is the electric field vector at that point, or the direction of it, at least so we can fill this in once again. One thing. We'll notice that the field lines are most dense around the charges themselves. And so just by drawing these, we can see where the electric field is the most positive. And you draw this perfectly accurately. I know what the general shape is, but what we do is we actually calculate the electric field at each point, and that gives us what the field lines look out look like. So this helps us visualize electric field because it's a very abstract concept. Yeah, So here I have another example this time with two positively charged particles near each other, and they have equal magnitude charge. Now we know what the electric field looks like. Right around one particle, a positively charged particle. Wanna get away as quickly as possible, so the electric field vector points readily outward. So what happens in in the area in between? Well, as long as it's closer to the particle on the right, the electric fields gonna point to the left. But as it gets closer to park on the left, obviously there's gonna be a fight back the other way. And so if we eventually, the electric field will bend downward. Cool and head off this way where I want to get away from both on this opposite side. The initial electric fields are dominated by the particle on the right. But as we get further and further away, the particle on the left starts to contribute on the same order as the particle on the right, and we'll see the electric field doctors bend away from both. I should mention the one example in the middle. That's special is what happens when we start at the exact centers of each. Well, we've shown already that here, right in between, there is no electric field. Electric field generated by the product on the right is equal and opposite to the one on the left, and they cancel each other out. And so So we know the highest density shows where the electric field is most powerful. They're gonna be extremely powerful in this region in between because we're very close to both particles except will always be empty right in that center spot because they cancel each other out and there is no electric field or the electric field is zero at that point. Just to reiterate these lines, I don't mean that the electric field is the same magnitude throughout that line, instead of what it really indicates is if we place the charged particle here a positive charge, it would follow this path because tension Thio every point on this is the electric field or any of our. Conversely, if we place a negative charge somewhere here, it would follow the path back along that like electric field line.

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Electric Potential

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