studiot

I am guessing that this is the movement of a charge q along a line L from A to B in an electricfield E. In that case this would be an energy balance saying that the work done intergral (E.dl) equals the potential energy gained. Did you miss out a dot in the first integral?

Difficult to offer more specific advice, without more specific information. Like what laptop is it and how do you know only the screen is cracked - what are its symptoms?

Indeed so. It's a question of obtaining the correct part.

Changing a broken screen is not difficult and takes about 20 minutes. Depending upon the laptop a new screen can cost from £30 to £90, although the laptop manufacturer would probably charge between £150 and £250. You said it was an old laptop and screens for many old laptops are no longer available, though some suppliers supply modern substitutes. You can also find laptops of similar models that are broken for some other reason eg failed motherboard very cheaply and do a transplant that way. You will need a few of the correct tools and some care in handling the parts however.

Thank you for all this information to digest. I am still interested in the engineering mechanics of things, and you have not answered my question about impulsive forces, or water levelling. Here is a question from a modern textbook on fluid mechanics, that might be of interest. It is about hauling 'buckets' of water up inclined planes.

I suggest you look at posts 20 and 21 for definitions of terminology. I think this thread is not the place to discuss Us v Uk terminology, although I would be happy to in a new thread set up for that purpose. Unfortunately your comments on the screwdriverd are unsound. ( as a matter of interest the most recent US authority on the subject, Sokolnikoff, late professor of mathematics UCLA uses the term couple when describing this situation, p107 of his book) With the screwdriver located into the screwhead, the screwdriver itself is subject to torsion when a couple is applied to the handle, whether the screw moves or not. The difference is that if the screw moves it is obviously not in equilibrium, whilst moving. Torque and tosion and the relationships between them were defined by engineers for sound engineering reasons to distinguish them from ordinary couples and other turning effects and many engineering relationships and formulae have been developed that just will not work using the looser definition of a torque being a single couple around and axis. An unrestrained 'torque' situation with the unengaged screwdriver cannot work for much the same reason as others have been telling Relative you cannot apply a torque at the centre of rotation.

Internal energy is a concept that you will not need until university, but it is really a very simple idea. Internal energy is not another particular form of energy like kinetic energy or potential energy under gravity, which you may have met. It is a sort of energy piggy bank to take account of all possible sorts of energy that a body or bunch of molecules or whatever may have. This includes potential energy, which is probably why fuzzwood said what he said. But it also includes kinetic energy, electric energy, chemical energy and heat energy. So if we heat something up the specific heat energy we input adds to its internal energy. This also applies to latent heat. The branch of science that studies how one form of energy can be exchanged for another is called thermodynamics. So you can imagine the internal energy bank as like your money account where you put dollars in and take euros out.

+1 swansont. Bignose's ruler experiment was designed and offered to show relative the exact opposte!

Wow batman !*#!

No, why would I? You have changed what I said, why? I agreed with the following statement you made. Perhaps it's my eyesight but I cannot see torque mentioned. I would agree, and have stated this, that torque cannot be applied without mass since all physical objects have mass at the classical scale. Let me try one last time. Take a screwdriver in your hand and turn it in free air. Your hand is applying a turning effect to the handle The screwdriver rotates as a whole There is no twist or torsion There is no torque Now insert that screwdriver into a screwhead and turn it. Your hand is applying a turning effect to the handle The screwhead is applying a counter turning effect to the bit There is twist and torsion in the shaft That is the sitution where torque arises If the turning effect is greater than the counterturning effect then the shaft will not be in equilibrium and will spin or rotate. This is the situation where an engine develops torque and cannot occut without all the components being in place.

In further consideration of my last post consider a battery connected to a circuit as in fig1. Conventional current flows from the positive terminal of the battery (Q) to the negative terminal through the circuit. Electrons flow from the negative terminal (P) to the positive through the circuit. Circuit Voltage is reckoned as shown so that V = (Vq-Vp) and has the sign convention that increasing voltage get more positive. Now reverse the signs on the charge so that electrons are now positive. Note that we cannot physically reverse the battery so Q now becomes the battery negative and P the battery positive, and that electrons still exit the P terminal, regardless of its sign. There are choices of adjusting the other conventions. We can leave everything else the same as in Fig3 But hey, Say we have a 10 volt battery and the circuit is a simple 10 ohm resistor so I is 1 amp, what happens. Well Taking Vp as zero and using our definition V = (Vq-Vp) = ((-10) - (o)) = -10 What minus 10? What happens now? Well that means that we are putting in (-10) * (1) watts to our resistor = negative 10 watts. so the sign convention is now at odds with most thermodynamic conventions that energy in is positive. and what about good old ohms law? Well we have to add a minus sign so that V = -(IR) OK let's abandon this and revers our definition of votlage as in Fig2. Note it is now again opposite to the direction of current. We will now recover positive signs in our power and ohmic calculations. But we have had to change two conventions to achieve this.

Since I would rather say something positive this is the (only) part of your last post that is correct. The inertia is another name for inertial mass.

Rubbish. Most torques arise from couples, not forces but not even they are strictly necessary. Unless you wish to tell me that the Wankel engine produces zero torque and can therefore not drive a vehicle? I have told you that the physical quantity you need to consider for a massive object whirling around on the end of a rod is called moment of momentum or angular momentum.

Are we talking about the buttons at the bottom of each post, labelled "Quote" and "Multiquote" ? I agree with JohnCutherber they are so clumsy as to be an embarassment to a scientific site. I have never been able to get them to do what I need. The speech bubble icon on the toolbar is simple and works moderately well, though it has its idiosyncrasies.

Torque may be produced by linear force that twists, or it may not. But it is not force. Many have said this to you repeatedly in this thread.

Hello MigL Actually I think the Sorcerer gave an appropriate view of his proposition by reversing all signs. He just was not using the correct term. Communtation, which you have correctly stated, is a different process. Also the Sorcerer was wrong in only considering multiplication. Consider addition and subtraction of A and B versus -A and -B 7 - 5 = 2 but (-7) - (-5) = -2 ie a sign change So if are using signs to denote direction and polarity and then we swop all signs and subtract, we have a sign change.

Bignose offered you a simple experiment in post#15 of this thread and from your favourable response I thought you had tried it out. Have you forgotten already? My experiment in the other thread had nothing to do with Euler.

Euler axes are only regular rectangular axes. The ruler experiment that Bignose offered corresponds to moments (I know that modern americans call these torques) on 'Euler axes' and what happens to the ruler if you apply them? Interestingly they came up in the guise of Euler instability in post#4 of this current thread about Chaos Theory. http://www.scienceforums.net/topic/85959-questions-about-chaos-theory/ If you take a brick, book or cigarette packet, it has three Euler axes. If you hold it between your hands by opposite faces, (thus picking out an axis) and toss it into the air, spinning, then the following occurs For two of the three pairs of faces the spin will be stable. (ie spin about two of the axes) For one pair of faces the spin will rapidly degenerate into a wobble that gets bigger and bigger until the object tumbles instead of spinning. Try it and tell me which axis this is. It is always the same one.

The Lorenz equation has nothing to do with torque. I would challenge any expert to show me a torque applied to a torque wrench or screwdriver with the above definition as the only input.

Of course, but why only anticlockwise? There is only angular momentum if mass is involved in the rotation. Torque (in my opinion) only exists if that rotation is twisting something physical. The practical experiments I drew you attention to are designed to show these ideas. alternatively the classic example is the rotating garden sprinkler, these can also be fun to experiment with.

This is all interesting information and I will think about it before replying. Meanwhile did you understadn what I meant about impulsive forces? , you didn't mention it. And what did you make of my comment on levelling? Do you understand the significance of correct alignment and fit and horizontality for the structural integrity and longevity of the building?

The statement is also known as Poinsot's Theorem (1804). Turning effect type 2 in my list - the couple is an example of this. A couple is composed of two equal and opposite parallel forces. Because they are equal and opposite and parallel they balance as forces, but a turning effect is left. If you look at the other thread on difference between a couple and a moment is that the moment of a force is different about every point in the plane, whereas a couple is the same for every point in the plane. Also not that a moment and a couple are 2 dimensional and a torque is 3D in that it transfers the turning effect from one plane to another in 3D.

I take this as an agreement with my post to which is was a response, so when are we going to get on with it?

OK, there are several turning/twisting effects and torque is one of them. Here is an extract from a thread started by someone with the same questions you have There are some useful sketches in post#10 and another simple experiment like Bignose's in post#16. http://www.scienceforums.net/topic/80386-is-there-angular-force-tangential-force-why-is-tangential-f-scaled-twice-for-torque/?hl=torsion#entry780312 Like subliminal I think you orignally were seeking a quantity called moment of momentum or angular momentum. Structural and mechanical engineers use the terms torsion and torque to distinguish between the turning or twisting along the long axis of a shaft or structural member and the bending moment across the structure.

The short answer is that some equations would change and some would not. But you would not get rid of the inconsistencies by declaring electrons positive or by making conventional current flow from negative to positive.