- #1
Jewish_Vulcan
- 88
- 4
for example when you climb up an inclined plane why is there no work in the horizontal direction yet there is work in the vertical direction? I do not want examples I want a direct answer.
I know knew that all along but it seems like there are still forces acting in the horizontal direction like the legs being pushed forward maybe...In the definition of work, the work done is the product of your force vector and your displacement vector which works out as |F|*|d|cosθ where |F| is the magnitude of the force, |d| is the magnitude of the displacement and θ is the angle between the two.
What happens if θ = 90 ?
cos90=0, I found that out a while ago but why is it cos and not sin?
I know knew that all along but it seems like there are still forces acting in the horizontal direction like the legs being pushed forward maybe...
There would be no horizontal force for a rolling boll on a flat surface ehh?A person is a bad example to use. The human body is a very inefficient machine and it takes work just to keep walking forwards on a flat plane. Replace 'person' with a rolling ball or something and assume no friction.
It comes down to what is meant by the vector dot product in, [itex] W = \vec F \cdot \vec d = |F||d| \cos \theta. [/itex]cos90=0, I found that out a while ago but why is it cos and not sin?
the answer is: the force in the horizontal direction has a net of 0, when they say for a certain distance like 10m they make you "assume" that the person came to a stop after the 10 m, for him to come to a stop an equal but opposite force must act against the motion. because w=fd, w=0(10)=0, so please put away the calculus
then describe how the net force is 0 in the horizontal direction please.That doesn't look correct to me. There's no reason to assume they come to a stop after 10 meters. What happened to the person before or after encountering the inclined plane doesn't matter when it comes to understanding the work done.
then describe how the net force is 0 in the horizontal direction please.
I understand that you do not agree with me but I do and I gave a logical reason... I do not mean to be rude to a staff mentor but I may believe you if you give me a reason...I don't see what the person is doing before or after the inclined plane has to do with the net force while moving up the plane.
I understand that you do not agree with me but I do and I gave a logical reason... I do not mean to be rude to a staff mentor but I may believe you if you give me a reason...
I did not see a scientific reason that stated why there is no work in the horizontal direction for say a person walking forward on a flat surface, please restate your reason of why there is no force in the horizontal direction. So far the only valuable information I have obtained from you is "What happened to the person before or after encountering the inclined plane doesn't matter when it comes to understanding the work done.", You could be correct but I would need other members to agree with you to convince me that you are correct. Furthermore that qoute does not explain why or how there is a net force of 0 in the horizontal direction.What are you talking about? That was my reason.
I did not see a scientific reason that stated why there is no work in the horizontal direction for a person climbing up an inclined plane...
I did ask if that explination was correct on a question about work on an inclined plane, chestermiller and brainpushups replied to my conclusion and said it was correct, that is why I am agrueing with you. I have not even graduated general physics yet so maybe you should talk to them about why you think they are wrongBecause of the reasons stated earlier in the thread. Re-read them and if you have questions on what's been said, ask. Don't just throw out an explanation and then demand that we explain why it's wrong. That's a bad way to learn.
I did ask if that explination was correct on a question about work on an inclined plane, chestermiller and brainpushups replied to my conclusion and said it was correct, that is why I am agrueing with you. I have not even graduated general physics yet so maybe you should talk to them about why you think they are wrong
here is the thread about the different but similar subject: https://www.physicsforums.com/threa...s-for-work-problem.794786/page-2#post-5000178
You have asked your question and it has been answered. As has already been explained, a person walking on a flat surface does have to apply a force to keep moving, and as a result, the person does perform work to keep moving. A simpler example that might be easier to understand involves a smooth ball rolling on a flat, frictionless surface. Since the ball doesn't have to overcome any forces (including friction and gravity), no work is performed.I did not see a scientific reason that stated why there is no work in the horizontal direction for say a person walking forward on a flat surface, please restate your reason of why there is no force in the horizontal direction. So far the only valuable information I have obtained from you is "What happened to the person before or after encountering the inclined plane doesn't matter when it comes to understanding the work done.", You could be correct but I would need other members to agree with you to convince me that you are correct. Furthermore that qoute does not explain why or how there is a net force of 0 in the horizontal direction.
Yes they are horizontal forces, but neglecting air resistance they average to zero over time, if initial and final speeds are equal.I know knew that all along but it seems like there are still forces acting in the horizontal direction like the legs being pushed forward maybe...
I'm not at all clear what you are saying here, and maybe others have misinterpreted it.the answer is: the force in the horizontal direction has a net of 0, when they say for a certain distance like 10m they make you "assume" that the person came to a stop after the 10 m, for him to come to a stop an equal but opposite force must act against the motion. because w=fd, w=0(10)=0,
Umm... if it's rolling, why do you care about friction?A simpler example that might be easier to understand involves a smooth ball rolling on a flat, frictionless surface
Mark44 said:A simpler example that might be easier to understand involves a smooth ball rolling on a flat, frictionless surface.
I guess if the surface is frictionless, the ball would just slide. The frictionless restriction was to eliminate the consideration of any horizontal forces impeding the motion of the ball.Umm... if it's rolling, why do you care about friction?
that is why I posted this thread, in the general physics homework problems they did not specify the before conditions and after conditions so I did not see why the net force in the horizontal direction was 0. your information was helpful and verified my understanding.i'll suppose you mean something like "A man weighing 700N walks on a horizontal path for 10m in 15 seconds. How much work does the man do?"
I would first criticise the problem statement for not specifying whether the man was already walking before the 10m started, nor whether, as you say, he came to a stop at the end of the 10m.
yes that agrees with my conclusion, thank you for the reply.you've got all the math in the world by other answers, but i think they all missed to clarify something - perhaps they all consider it too obvious.
or it's already said but i didn't spot it above, i only skimmed.
anyway, i think it all comes down to which force's work are you actually looking at.
there is of course positive work done by whatever is pulling the object, as well as negative work done by the friction forces slowing it back down.
there is no work done by the force of gravity.
and a force is a force... whether it is used to lift a body, accelerate a body or move the body against friction, its all a force and , times a distance , you get "work".yes that agrees with my conclusion, thank you for the reply.
Umm... if it's rolling, why do you care about friction?
If it's rolling, the presence or absence or degree of friction with the surface makes no difference. You may be thinking of rolling resistance.rolling can still have friction.. "rolling without friction" allows you to calculate the work used strictly to move the object from one point to another.
Yes, im speaking of rolling resistance..... is there any other kind that wouldn't make a difference? :)If it's rolling, the presence or absence or degree of friction with the surface makes no difference. You may be thinking of rolling resistance.
If there's rolling resistance, that will apply equally with or without friction. The difference is that with friction both rotational and translational speeds will fall (in step); without friction only the rotational speed is affected - but as soon as that happens it is no longer considered rolling.Yes, im speaking of rolling resistance..... is there any other kind that wouldn't make a difference? :)
never hear about this type of stuff, would it only be affected without friction if the ball was not a perfect sphear? if not how would it lose any rotational speed?If there's rolling resistance, that will apply equally with or without friction. The difference is that with friction both rotational and translational speeds will fall (in step); without friction only the rotational speed is affected - but as soon as that happens it is no longer considered rolling.
It's not the shape, more the rigidity.never hear about this type of stuff, would it only be affected without friction if the ball was not a perfect sphear? if not how would it lose any rotational speed?