Recent content by sk1105

Thanks everyone for the useful responses. What I want the program to do doesn't really lend itself to 'else if', but I tried nesting the statements and it yielded a noticeable speed improvement since the conditions are quite complex and the program no longer needs to check condition A three...

Currently in my C++ program I have something like if (A){ do thing 1; } if (A && B){ do things 1 and 2; } if (A && B && C){ do things 1 and 2 and 3; } and so on. Unfortunately this has to be done for a very large sample and it takes quite a long time. I was just wondering if it's more...

When you say that friction opposes relative motion, you are being too specific (although one could actually be more specific by saying that the motion has to be between two objects in contact, in a direction parallel to the contact plane). What you should really say is that friction is a force...

In the unlabelled equation between 11.19 and 11.20, notice the presence of ##\hbar##. The reduced Planck constant has units ##Js##, which combine with the ##s^{-1}## from the derivative to leave just ##J##, the units of energy. Explicitly, we have ##[\hbar]=kgm^2s^{-2} \cdot s=kgm^2s^{-1}##...

Acceleration should be in miles per second per second (mi/s##^2##), perhaps you mistyped. In the question it says that the speed is increased at a steady rate, so the acceleration should be the same at any time t<5, so you should be able to work it out from the initial and final speeds. For the...

What do you mean by mobile radiation? Assuming you mean the electromagnetic radiation that a phone sends to the nearest tower, then yes, flight mode deactivates all these communications.

I think the motivation behind the initial complaints was specific - "Hannah has some sweets...show this equation" seemed like too large a leap in reasoning for a lot of people. But it's also fairly probable that a large number of students just couldn't do the question but haven't thought about...

Those are the only reports I've seen as well. I think the media have catastrophically over-hyped this, with headlines such as "The 'impossible' maths question solved". Indeed, the fact that the reports I've seen all focused mainly on the students' Twitter posts and did not even mention teachers...

Your hand pushing down on the book will increase the normal force at both interfaces, so at the book/table interface the normal force will be caused by your hand pushing down as well as the book's weight.

Yes it turns out that was part (b), however since part (a) is a "show that..." question, its solution is not necessary for the second part, and the complaints have been directed towards part (a). I entirely see your point about hand-holding though, and I agree your suggested wording of the...

A lot of school students in the UK are making quite a fuss at the moment about a question that appeared on a recent GCSE maths exam (GCSE exams are taken in the UK by 15/16-year-old students). The discussion has since spawned its own Twitter hashtag, a variety of memes and has been covered by...

Microsoft has just placed an icon on my taskbar inviting me to sign up for my free copy of Windows 10 when it becomes available. Ordinarily I would go for it (upgrades must be better, right?), but given the complaints levelled at Microsoft's last OS I'm not so sure. I currently have Windows 7...

Yes you can. A matrix is essentially just a compact way of specifying what action to perform on each component of a vector to make another vector, and can contain whatever you want. Is there something you've seen or heard that made you think fractional indices weren't possible?

Yes you're right, my bad. That makes sense, I was just getting muddled with all the vector components. Thanks for your help.

Homework Statement The free Dirac equation is given by ##(i\gamma ^\mu \partial _\mu -m)\psi = 0## where ##m## is the particle's mass and ##\gamma ^\mu## are the Dirac gamma matrices. Show that for the equation to be consistent with Relativity, the gamma matrices must satisfy ##[\gamma ^\mu...