studiot

I'm sorry I don't follow this. These are these are all calculable (which means I get these answers) from the information given. I would say a calculation scheme would run like this, parts (a) and (b) being to calculate the velocity of the ball at impact and the velocity of the ball and block immediately after impact. 1) Calculate the velocity of the ball at impact by equating the potential energy gained from its fall from its release position to the kinetic energy it has at impact. This does indeed yield 7m/s. 2) We may then obtain the post impact velocities of both ball and block from conservation of both energy and momentum simultaneously. This yields -2.33m/s for the rebounding ball and 4.66m/s for the block. Notice the negative sign on the velocity of the ball. 3) The force of static friction does no work. So no kinetic energy is lost overcoming static friction. This is why Ron's answer is correct. The KE acquired by the block from the ball is given by using the immediate post impact velocity of the block in the usual expression for KE. 4) The block moves a distance d against the constant resistance, R, of kinetic friction. This therefore does do work, dissipating the KE of the block in distance d, therefore doing Rd joules of work. Equating this to the KE of the block plus should yield d.

Since you like exhibitions another good one is the home of photography, the Fox Talbot Museum https://www.nationaltrust.org.uk/lacock/ Also worth a visit is Futuroscope in central France the Museum of the Moving Image http://en.futuroscope.com/ And there is a museum in that is in the making inYorkshire concerning the recently discovered pioneer of moving images. Sorry there is no link for that yet.

Continuing the theme of Art in Science Who has seen the BodyWorlds exhibition? Highly recommended, but is is Art or Science? http://www.life.org.uk/whats-on/body-worlds

I am trying to keep this discussion friendly. I think we are agreed on the merits and demerits of the problem in hand. It's just in the presentation we can surely agree to differ. Unity+ can then have the (luxury) of two different points of view to choose from. He is a first rate student and I have a lot of confidence in him. I didn't say otherwise, however since you ask I believe it's called fluid pressure. A vertical force (acceleration) due to gravity becomes a horizontal force (acceleration) within the fluid. It is also true to a less obvious extent that in solids a vertical force (due to gravity) becomes a horizontal shear force.

How can you say that? Are you not considering it by saying it does not work? All I have asked for is sufficient justification to exclude it. I was taught to start static analyses with the words "As in equilibrium." At the tiem I thought "what an unnecessary fuss. But the number of poster I have seen here here carrying out inappropriate equilibrium analyses on systems that are not in equilibrium justifies it in my hindsight. You have also talked about gaining extra marks for a good discussion. You can also earn extra marks (or at least prevent loss of marks) by justification statements so even if (as here) the strain energy calculation went awry the statement Total energy of system = Strain energy + Potential Energy + Kinetic Energy = A constant Would earn part (or even half) marks. And in the real world outside proper annotation and documentation can help understand the flow some time alter.

It's not unnecessary in this case since the original analysis was flawed. Further this analysis is also suspect What is x? I have already said we need a diagram. How many elastic forces are acting on the ball? In my diagram the orientation could be vertical, in which case there are opposing vertical forces to consider It could be horizontal or somewhere in between. It then becomes necessary to prove that there is no exchange of energy between horizontal and vertically acting agents. See my comment on the pendulum at the end. I also am not sure what the dimension x represents, because if it is as I have shown then it is not the elastic extension of the band. As to conservation of energy and resolution into components. I do not think for one minute that I have anywhere implied you cannot or should not resolve vectors including forces. My intention, since it is an important technique, has always been quite the reverse. I' ve tried to carefully avoid say horizontal or vertical energy, rather to indicate what may be correctly attributed (resolved) into such directions. If you consider the humble pendulum and gaily state that you may gaily separate the energies into horizontal and vertical you will come to inappropriate conclusions. The total (mechanical) energy is constant. In the centre of the swing it is all KE and the motion is purely horizontal. At the ends of the swing it is all PE and the motion is purely vertical. Everywhere else it is some combination of both. So there is an example mechanical system where gravitational PE and the energy due to horizontal motion are interchanged.

Reading my previous post I realise you might I thought I was inviting comments on JC, so I apologise for the sloppy posting. I meant that was the start of my comments on the physics of the question. Conservation of energy (from which the balance equation is derived) applies to the total energy. You cannot just take a bit of the system's energy and equate it to another bit. Just taking the "horizontal energy" implies we can resolve energy into components, which is not true. Any of the energies can be converted to any of the others, given the right circumstances. If we do ignore some energy we should always show why; for instance there are no magnetic forces acting, or if we can say that a particular energy is constant, we can ignore it. Neither the gravitational PE nor the kinetic energy due vertical motion are contant. Similarly the calculation of the time of flight stems from the constant acceleration equation s=ut+0.5ft2 Had the zero term been included here the nonzero term in the energy balance might not have been missed. This may be considered a philosophical point or excessively pedantic, but many questions are fluffed simply due to missing part of the system.

Was this another of those experiments designed by that well known Physicist, JC (John Clees) from the Ministry of Silly Questions? It rather reminds me of a GCE practical from long ago when we had to measure surface tension by floating a needle and then dragging it up the meniscus with a magnet. Comments? I can't easily think of a worse projectile. Pingpong balls are designed for maximum interaction with the air. You need something small and dense to minimise air interaction. With the proviso that air resistance can be ignored (not at all true here) your kinematics equations are correct. However there are several questions relating to your energy analysis. Well there was not diagram so I can't tell was acting double or single. Any catapault/bow arrangement applies the tension double, but at an angle. So is the constant calculated for a double band or single? Further is your x distance in the strain energy term in your equation correct or should it be 0.17 cos of some angle? That is: Do the forces in the elastic act at an angle to the displacement? Again a diagram would help. Finally concerning imatfaal,s point 4. Energy is a scalar so does not act orthogonally to anything. Your energy balance is lacking a term as is your kinematic analysis. This does not matter in the kinematic analysis since the term is zero at launch, but does affect the energy balance. The intial vertical velocity is zero. Upon striking the ground the ball has acquired a vertical velocity, whose kinetic energy exactly equals the loss of potential energy due to the vertical drop.

With respect should that not be infinitesimally close, infinitely distant?

Ha Ha, but There was a serious message in my comment. Are you familiar with the story of the famous Ancient Greek Philosophers and the Horse's teeth?

Bear in mind this thread is about art v (sorry Mike) in science, and so we are comparing the art with the (applied) science in the bridges.

Is this art or science Here are 6 possible arrangements of a motorway overline bridge crossing twin carriageways. Which do you prefer to approach? Which do you find most aestetically pleasing? My apologies for the squashed nature of the sketches. It is interesting to note that Arrangements 1 to 6 are arranged in increasing order of cost. They are also arranged in decreasing order of accident rate.

So you have the heat equation in a chimney. x is bounded but y is unbounded, but the question helpfully points out that u is bounded everywhere (=remains finite). When you separate the variables, the fact that u is bounded rules out many possible candidate functions for X(x) and Y(y) since X(x) must be bounded in the rannge 0<x<1 and Y(y) must be bounded in the range 0<y<infinity so for instance ex is admissible but ey is not since this tends to infinity (is unbounded) as y tends to infinity.

I don't think Aristotle will ever live that horse down.

Hello Unity+, It is not clear whether this is a science or legal question, but seems to be more legalistic. In science(particularly mathematics) we have (dis)proof by counter example. It only takes one counterexample. In UK law we distinguish between Civil matters and Criminal matters. The big difference is the amount of proof required, called the 'burden of proof'. For Civil matters the burden of proof is substantailly lower. The common phraseology is In Civil matters the burden of proof is decided upon "The balance of probabilities" (in the evidence presented) In Criminal matters the burden of proof has to be "beyond reasonable doubt", which is much more onerous. However the burden of scientific proof is substantially higher than either of these.

This is an easy experiment to try for yourself. Don't be a Greek and guess. See if you can then explain the results.

Thank you both for your good thoughts. I must get MikeSmithCosmos to draw me some pictures of elbow grease.

Thanks, Worth a try it before I go to bed, but dishwasher stuff is similar to persil ie washing soda plus polyphosphates so I'm not sure. I know printers used to use large quantities of benzene to clean things up, but I don't have any.

Well 1000mg is 500 times as much as 2mg So you will need 500 times as much volume as for 2mg ie 500 x 100 microlitres.

I have a pair of miniature National Trust wellington boots at a pen holder that has become encrusted inside with old ink and other detritus from the pens. I am looking for suggestions as to how to clean this out. So far I have tried white spirit petroleum spirit caustic soda, drain cleaner hot persil solution without success Cleaning suggestions welcome. The wellingtons are made of thick pvc or polyethylene.

Genecks, thank you for taking the interest in some of my posts in this long thread. They were all intended to promote discussion, not stifle it. As regards your comments: Good point. I am at a loss on this one since your reply was not about the last three lines I wrote. These you also quoted elsewhere. So there may have been some mix up somewhere. I will deal first with the material you appear to have replied to, namely the clockwork universe. I do not agree that this is the same as the block universe, particularly as described by Einstein. The essence of the clockwork universe is cause and effect and predictability (= determinism). That is a given cause will always give rise to a specific, calculable and predictable effect. So given enough information a superbeing could, in principle, predict the future course of the entire universe. This view requires that time flows from past to future. Einstein's view of the block unverse was that time does not flow from past to future in his words "it just is". That is the essence of the block universe. But this is a digression from statistics. Back to my last three lines. these were about the same subject expanded on in my post103. Namely the difference between analysis and synthesis. In particular they were about the use of statistics in the synthesis process. Finally the OP philosophy. So far as I can see this may be summed up as. The OP rejects statistics and seeks a deterministic world. That part is fair enough and makes for a good discussion. However the OP goes further and accuses the professionals of a world wide conspiracy to suppress objections to statistics. IHMO This part is both seriously misguided and insulting to professionals who spend their daily toil dealing with the fact that they know all too well they do not have (and never can have) all the information. This situation is most evident in the synthesis process.

Yes it is the condition for this

It is interesting how this relates to the safety factors I was talking about.

+1 to Bignose for have far more patience than I do and for putting many of my thoughts more politely than I could. There is one further point, howevr, that I mentioned in post36, that has not received sufficient attention. All the discussion about statistics so far in this thread has been about analysis. It is far, far easier to find formula to analyse something that is already there (or given). A rocket of mass, m ; a cylinder of gas of volume, V and so on. than it is to put something specific in place. This process is called synthesis and statistics has greatly helped improve Man's ingenuity in the real world to synthesise. For instance if you have a valley, there is no formula that says bridge = XXXX or roadway embankment = that The design of such a bridge or embankment is part of the process of sythesis and statistics plays a vital part in the modern world of design. Again when someone goes to construct this embankment, there is nothing there to start with. Just uneven, sloping ground. He knows where the top of the embankment is to end up But he has to start at the bottom and build up. So what does he say to the first lorry driver who says here is your first load of fill material, where shall I dump it? In other words where is the edge of the base of the embankment? Incidentally statistics will not help answer this question, any more than deterministic geometry or mechanics. In school most questions are about analysis and usually deterministic. It can be a great shock on entering the real world where most activity is about synthesis and neither deterministic or even capable of being expressed by formula.

To quote M Escher Note : both artist and purely objective rules are mentioned. So was Escher artist or scientist or a mixture of both or neither?