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/sci/ - Science & Math

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11225766 No.11225766 [Reply] [Original]

physics major here.
I had an argument with my teacher whether or not friction can do positive work. I said when a box is on an operating conveyor belt, friction is the only force moving it, so that means the work done by friction has to positive, not negative

>> No.11225794

>>11225766
You didn't take into account the forces moving the belt.

>> No.11225902

>>11225766
>physics major here
Larp.

>> No.11225959
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11225959

>arguing with the professor

>> No.11226048

>>11225766
Oh god, you sound like the one "smart" kid in class who feels like he has to mentally masturbate in class to show how intelligent he is. Not to mention that fact that you're not even correct here. The nature of what friction is means it can't be positive since it opposes motion.

>> No.11226058
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11226058

>>11226048
>The nature of what friction is means it can't be positive since it opposes motion.

This pic is obviously what OP means.

>> No.11226060

>>11225766
You are wrong. The traction force on the wheels of a car, for example, is a sheer force from dry *static* friction. The force acts over no distance and it does no work. The torque on the drive wheels is what does all the work.

>> No.11226073

>>11225794
>>11226060
If the system is defined as JUST the box, then there is only one relevant external force acting on the box, which is static friction. And that force is causing the system's kinetic energy to increase. It's just dependent on where you draw the bounds of the system.

>> No.11226078

>>11225959
This.

>> No.11226093

>>11226048
>it can't be positive since it opposes motion

Then what force is moving the boxes fuckwit?

>> No.11226094

>>11225959
>>11226078
>>11226048
>no anon you must remain quiet when your professor is near, only speaking to thank him when he commands you to lick his asshole
You autists obviously don't know what it's like to actually form a decent (professional) relationship with a professor. I would have these kinds of conversations with my main physics professor all the time. I'll still shoot him an email every now and then to pick his brain or try to get him riled up about something.

>> No.11226095

>>11226073
>>11226060
You can't call it static friction if the surface is moving

>> No.11226107

>>11226095
You can name it whatever the hell you want. All it is is electromagnetic repulsion on an atomic scale. Don't cling so tightly to textbook concepts.

>> No.11226119

>>11226107
By that dumb logic, friction can't do negative work either.

>> No.11226122

>>11226119
?
Any force that can be exerted on a system can do either positive or negative work on the system.

>> No.11226133

>>11226093
Friction causes the box to rest on the conveyor belt, which is moving.

>> No.11226165

>>11226122
So because friction is a force, then by definition, friction can do positive work

>> No.11226170
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11226170

>>11226133
>Friction causes the moving box to rest on the moving conveyor belt

>> No.11226179

>>11226165
Yes

>> No.11226199

>>11226179
That was literally the entirely point of the thread