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University of Michigan - Ann Arbor
Simon Fraser University
University of Winnipeg
0:00
Aditya Panjiyar
(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?
Muhammed Shafi
04:15
Kathleen Tatem
(II) According to a simplified model of a mammalian heart, at each pulse approximately 20 $g$ of blood is accelerated from 0.25 m/s to 0.35 m/s during a period of 0.10 s. What is the magnitude of the force exerted by the heart muscle?
03:27
Kai Chen
(I) A constant friction force of 25 N acts on a 65-kg skier for 15 s on level snow.What is the skier's change in velocity?
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welcome to our section on the difference between conservative and non conservative forces. If you remember in the past we had talked about how conservative forces we're related to these restoring forces so far. We found two of those gravity and elastic forces. And then we had non conservative forces which were related to the dissipated forces that we saw previously, including things like friction, and we'll find that there's many, many others. In fact, it's rather difficult to be a conservative force. There's certain requirements that you have to it based on what we've talked about so far, uh, those requirements being that first of all, it can be expressed as the difference between the beginning and end of potential energy. So that is to say, it's equal to negative. You final minus you initial. So we need to have some associated potential energy function, and all that matters is the final and ending points to Then it has to be reversible, meaning that if we put energy into it, we have to be able to get energy out. For example, if you do the work to stand up on top of a chair, Okay, you went up, but then if you step off the chair, you immediately get your energy back in the form of velocity until you hit the ground. At which point the normal force, which is not generally a or really, ever a conservative force, um, stops you and takes energy out of the system. Okay, so it has to be reversible. If you put energy in, you have to be able Thio into that potential energy system. Then you have to be able to get energy back out of it. Once again, number three, it has to be path independent. We already talked about this property in a previous video. But what it means essentially, is that because all that matters is the final and initial position. You should be able to take any path. You darn well, please. And still end up with the same change in energy between the beginning and the end. So the work done by a conservative force must be path independent. Okay. And then finally, when we have the starting ending, points is the same. The total work has to be zero. So if we have circular motion, for example, we're starting at any points are the same then the work equals zero. So work equals zero of start and stop at the same place. And you can see this with both of the forces we've considered before for gravity and elastic potential energy where gravity will do positive work or negative work depending on the direction you're going. And so if you go down and then back up to the same point, you'll end up with a total work done by gravity of zero jewels because one half was negative and the other half was positive. The same thing happens with spring potential energy. So we're going to consider how it is that we can look at forces that meet all these requirements. If we run across any others, or what sorts of functions might step might define a force that would then satisfy all of these conditions. And once we've taken a look at that, will also consider this idea that we wrote before that the non conservative work is equal to the change in potential energy, plus the change in kinetic energy, and we'll look how non conservative work can actually pull energy out of a system. So far, we've only considered conservative work and how it keeps the mechanical energy conserved. But we also need to consider these non conservative forces, which are actually pulling mechanical energy out of a system, so we'll have a couple examples about that as well.
Moment, Impulse, and Collisions
Rotation of Rigid Bodies
Dynamics of Rotational Motion
Gravitation
Fluid Mechanics
03:52
03:06
04:59
05:02
