Question

Check all the boxes that correspond to froces that do zero work

Answer 1

Gravity on a plane flying horizontally
Thrust on a plane flying horizontally
Air resitance acting on a snowmobile
Tension from a cable on a traffic light at rest
You push a stalled car, but it doesn't budge
Friction acting on a softball player slilding into second base

Answer 2

@IrishBoy123

Answer 3

@agent0smith

Answer 4

let's start with a crude definition of Work.....Work = Force x Distance

So when a Force acts over a distance, it has done work in that direction

So, for the first one, is gravity doing work on a plane that is flying horizontally??

Answer 5

Yes. I think I know the ones that do zero work.
I think its the first one, the one about the cable on the traffic light, or and pushing a stalled car

Answer 6

i know where you are coming from on all of your answers. intuitively they are spotty-dog.

but i'm just wondering this. and let's take air resistance on a snowmobile.

is the snowmobile doing work on the air ( i say yes), or is the air doing work on the snowmobile (i say yes too, because i reckon negative work is still work......but maybe that is wrong??)

simple graphic that is everywhere in terms of the definition


if this matters to you, i'd get a second opinion from others

@agent0smith
@ljetibo
@osprey

Answer 7

did you finish this @Unofficialllyy ?!?!

Answer 8

yes, the ones i chose were correct. :)

Answer 9

are you stuffing them in a website?

Answer 10

Air resistance still does work, just negative work.

Answer 11

indeed sir

I totally agree that negative work is fine because [but how do you explain this rationally??] it's mostly about balancing equations.

Answer 12

I'm not sure what do you mean how do you explain this rationally? In general work is a funny thing, not really all that applicable.

You can think of it as if you've a coordinate system centered on an air molecule, the snowmobile hits it and pushes it around for a short bit the molecule experiences a force of equal magnitude but opposite direction as the snowmobile. This is guaranteed by Newtons third law. Thus the work F*s becomes -F*s? Is this what you're asking?

Answer 13

I mean the common description.....a force acting in a direction

Answer 14

that's how the brainwashing begins. the idea that work can be negative is not on the menu

Answer 15

but yes, that is exactly what i mean

negative work. which is just a balancing factor in various equations

Answer 16

i'm talking to myself

right?!?!?

LOL!!

Answer 17

The force has to be parallel to displacement to do work, but opposing direction is still parallel.

Answer 18

Negative work done by a force could also eventually turn into positive work done (once the object stops and turns around).

Answer 19

Why wouldn't work be negative? Mathematically it can be because to calculate work you have to take force F and the path s as vectors and do an integral of their dot product. To do that you have to pick some king of a coordinate system to do it in. The sign + or - is just a remnant of that choice of the coordinate system in this aspect.

Having negative work is often beneficial in TDM i.e. where negative work basically means the work the system is doing and we're not investing into it. I've heated a pot by doing some work and then placed it on ice, that system has lost heat by melting the ice - therefore doing some work.

It's all cool there, but in classical and electrodinamics works is so-so of a quantity.