Classical Physics

There's a thing I don't get about the electron work function of a metal: in this wikipedia article, they say it's the difference between the bottom of the image-charge potential and the fermi level (just look at the picture in the article). But the image-charge potential has no bottom - it goes as 1/a, a being the distance between the electron and the metal surface . How do you get around that ? Does one have to reach for quantum mechanics to get a bottom - just as when solving for the hydrogen atom's energy levels ? If so, how did the likes of Einstein do to compute a work function before ~1915 ? Thanks in advance for your help, McCrunch

2 questions: 1) Is the pull force of a (Neodymium) magnet cube (3/8" in this case) with side to side magnetizing through thickness, larger between a mild steel cube, same size, and the magnet or an identical magnet? 2) Same magnet: Is the pull force larger, if it is attached to a large steel plate instead of a cube the same size as itself, and if "yes", by how much? Thanks to all, who answer to this question!!! S

So I have been working on a tesla coil and I just finished the primary circuit. I decided to run it alone (theoretically the spark gap should jump) but nothing happened. Heres the setup. http://www.physics.gla.ac.uk/~kskeldon/PubSci/images/tesla3.gif 10kv 30mA AC neon transformer. Capacitor that I made (rated at 2911 pF and up to 20kV, by my calculations) inductor (haven't done calculations yet... just wanted to see if it worked. But its coiled outwards and has about 8 turns and 3inches<radius<7 inches) Help plz? I would think that it had to do with either the power supply (both lines are hot not just one, and theres an anti short system) or the capac…

How can X-Rays ionize air? (or other molecules)

Greetings SFN users. New to the forums so a big hello, hopefully my first question will be a productive one. I was sitting at work recently watching the clock tick by when it occurred to me... The point of the hands closer to the centre must be moving slower than the extremeties of the hands? What brought me to this conclusion is that the circumfrance of a circle closer to the centre has a shorter distance than a circumfrance of a circle further out from the centrepoint. Consider if I was to walk around the same running track, once on the inside circumferance and the second time around the outside circumferance. The second time would take me longer (c…

There is something that I had never been able to understand about the way electro-magnetism was formulated mathematically. In EM we say that the charge is the source of the electrical part of the field, and that the currents are responsible for the magnetic part. But what is a current? Why define such an entity? It seems to me that the current densities can be extracted from the charge density's function. Isn't there any mathematical way to get J(x,y,z,t) given just rho(x,y,z,t)? This is also relevant to aerodynamics/hydrodynamics/field theory etc...

Could someone please tell me what the definition of a coulomb is? and also what's the definition of the ampere? All the resources on the internet go in circles. Some say that the ampere is the flow of current at the rate of 1 coulomb per second. Others say that 1 coulomb is the charge per second in a wire which carries a current of 1 ampere.. These two definition are basically the same and they go in an endless circle... One wouldn't be able to define either one without the other..... So can someone please tell me the correct definition of the coulomb?

Hi Good Folks I've been looking at Boyles laws but I‘m still having difficulty visualizing the basic rules of transference of compressed air / volume and how to apply Boyle Laws. I have created a scenario below can anyone help me towards the understanding. Assume there are two compressed air cylinders. Cylinder A is volume 100m3 @ 2000psi. Cylinder B volume 10m3 and currently at normal atmospheric (14.7psi). Also Assume that the two tanks are connected and air can be moved from tank to another via necessary connecting pipe, valves and pumps etc. So A) If I were to open the connecting valve between the tanks I understand that the pressure would …

Why do cathode rays illuminate the tube in which they are present? Also why do they stop giving out light at VERY low pressures?

What is the currently used definition of the meter? (meter, as in the unit of measuring length..) Someone told me that, if wavelengths of all the emission frequencies of an atom were added together the total length would be a meter. Is that true? I haven't found any reference to that definition anywhere else...

I've questions to ask. Plz do reply it. 1- In which of the following cases, the weight of the body will actual? a)- free space b)- in the air c)- under water d)- at sea level 2- Weight of a substance would be the greatest when weighted in: a)- air b)- free space c)- water d)- at sea level Plz explain the answer too. I'll be very thankful to u.

AmI correct in thinking that both balls reach the ends of the tracks at the same time due to them having the same initial PE? The intervening route doesn't matter.

Say an object A changes it's velocity from -3 ms-1 to 0 ms-1. Commons sense suggests that this is a decelleration because the speed of the object is decreasing. However if this motion is drawn on a velocity time graph then the gradient will be positive. A positive gradient means acceleration... (correct me if i'm wrong anywhere above).. So we knows it's a decelleration but the graph says it's an acceleration.. how can you account for this discrepancy?

Hi Forum, I hope you can help settle a bet. The question is: Can a body (say a ball) spin about multiple axes at the same time? For example imagine a ball with its centre at the origin of x-y-z coordinates. If the ball is rotating about the X axes is it possible for it to be simultaneously rotating about the y and z axes as well? If it is possible is the resultant rotation simply the "vector" sum (or equivalent) of each of the individual rotations, just as the velocity of a moving body can be resolved into x, y & z components, and if so how does one "add" the individual components (direction and "speed" of rotation) to get a resultant spin? Thanks

Good afternoon everyone, I am posting a question about pull up bars, sorry it is a bit long-winded. I have a 'powerbar' which is this: http://www.ukfitnesssupplies.co.uk/products-Powerbar-Doorway-Chin-Up-Bar_POWERBAR.htm However the spring mechanisms in the folding arms are broken (No big deal) and the 2 prongs which secure the bar on the opposite side of the door exert too much pressure onto my (landlord's) doorframe causing damage. The cantilever method seems to work well though, and the bar you hang from is above the height of the door, which gives you more hanging space. I have looked into this, the 'iron gym': http://www.saunabelt.co.uk/iron-gym-pul…

By the hypothesis of Maxwell,Light is an E.M. wave, every optical phenomenon can be explained. Most optical phenomena,e.g. the Rainbow,,cannot be explained bij quantum physics. Why that preference for quanta. Fashion? Morp

I'm having trouble understanding one of the most basic electrostatic experiments. When silk is rubbed on glass, the glass apparently acquires a positive charge distributed throughout it, and the silk also acquires an evenly distributed negative charge. How can the charges spread evenly through insulating materials, and also, if they can move around in both the glass and the silk, how can the extra electrons in the silk not be able to move right back over to the glass that is touching it? How does it all work? Also, a website explaining all about electrostatics would be very helpful, as I have been unable to find a good one.

I have a vague understanding of simple electric motors. Something I don't understand is how the commutator reverses the polarities. It'd be great if someone could help me out.

If two stiff or rigid objects are connected with a stretched spring, it will apply equal opposite forces on the objects and pull them together (let's assume a frictionless environment). Since this is a closed system of free moving bodies, the net force on the system will remain constant (let's assume zero for cimplicity). If instead two chains are connected with a stretched spring, it will apply opposite equal forces on the two links it is attached to, which again applies opposite equal forces on the next two links and so on, until the whole chain has been influenced by the spring force. First I assumed that the forces simply propagate unchanged from link to link,…

When a [spinning] cricket ball is flying through the air is it rotating or is it revolving? I ask because here in the UK a cricket sports presenter is claiming that if you watch the cricket ball in super slow motion and in high definition on this particular sports programme you can "see the revolutions of the ball". I think he should be saying "you can see the rotations of the ball" because the ball is rotating about its axis of rotation similar to the Earth rotating about its axis of rotation once every 24 hours BUT revolves around the Sun every 365 days. Who is correct him or moir?

1. I am confused because all my physics was learnt some 40 years ago and I have forgotten how this issue is properly treated . Also all my units tend to lbs, feet, inches etc.....I have not kept up to date with the new units such as newtons etc. Being recently retired, I am trying to build something that requires the facility below: 2. I am inserting a cylindrical cannister through a seal at the bottom of a column of static liquid ( in this instance water). Diameter d inches, length L inches, depth h inches below the surface. 3. I realise that I will expend energy against 3a the force of the pressure (psi)"P" x the cross section area (sq.inches) x length "l" in…

Hi there, I'm new to this forum. Nice to meet you! Well, basically, I'm studying under the IB course and I have Mathematics, Physics and Economics as my higher level subjects. Now that I just finished my exams yesterday, I chanced upon MIT's OCW Courses on Physics by Professor Walter Lewin. After watching the lecture about centripetal acceleration, I had a random thought about the acceleration of objects on the surface of the Earth and wrote a short paper about it. However, I do not have any much knowledge beyond the basics, and I'm not entirely sure about the resultant acceleration. There isn't exactly much information about this on the web too. Acceleration …

is there any discussions on why gravity, which affects everything is the most weak force that we know of, what is the theory of a gravitational leak. I've heard of this through m theory...maybe there's something new Merged post follows: Consecutive posts mergedi know its a very strange idea, but i was thinking about the source of gravity and i realized that all the matter, and dark matter as well as the variable percent that we cannot detect should be creating a much greater force. I believe there is some research into this.

Hello, Recently I've been reading the wikipedia articles on orbital elements and orbital state vectors. I've used the equations to write a small program which calculates the elliptic trajectory of an orbiting body from its state vectors. The trouble is that all equations in the articles seem to assume that the orbiting bodys mass is neglible and that the barycenter (or center of mass) is placed exactly at the center of the heavier parent body. If I want to describe the trajectories of two bodies of nearly the same mass orbiting their barycentre (like in the animation below), the equations in the articles cannot be used. So, my question is: how do you cal…

It seems science accepts these as facts... energy comes from the sun, is a finite amount and cannot be created or destroyed. A lake has a finite amount of potential energy in the water, which was placed there by the sun. Man has learned how, by increasing the head(distance the water drops), size and shape of the penstock(inlet tube), to increase the amount of potential energy by just using simple mechanics. Where does that inreased amount of potential energy, developed by man, fit into the law of energy conservation?