Direction Definition and 999 Threads

Why does a bolt of lightning crackle into many different directions when it travels to the ground? Can a bolt of lightning be made to travel in straight direction, is it theoretically possible to understand and control lightning?

Hello. I want to know about the polarisation of lasers and I've been reading basically two kinds of answers for the question 'Is laser light polarised?' The first one is 'yes' and the second one 'not necessarily'. Let's consider a gaussian laser. Ideally its light is monochromatic and coherent...

Homework Statement The vorticity vector ##\vec{\omega} = \text{curl}\ \vec{v}##, defined as usual by ##\omega^{2}=i_{{\vec{\omega}}}\text{vol}^{3}##, is ##\textit{not}## usually invariant since the flow need not conserve the volume form. The mass form, ##\rho\ \text{vol}^{3}##, however...

Homework Statement The Force applied to an object is equal its mass times its acceleration Assume that the ball has a mass of 40g. What is the force due to gravity acting on the ball? Homework Equations F=ma The Attempt at a Solution F=(.04)(-9.81) I get a negative answer, does that mean...

Homework Statement Find power absorbed by resistor, capacitor and inductor. Find the total complex power absorbed by all the loads.[/B] Homework Equations KVL/KCL The Attempt at a Solution I want to solve this using Mesh analysis. There is a supermesh where the 5A source is, so I start it...

Homework Statement Write a program to find the equivalent resistance between two opposite corners within a grid of "infinite size" with resistors between each point. So basically we have an infinite cube made up of cubes with 1 ohm resistors between each node. Homework Equations Kirkoff's laws...

Homework Statement A horizontal circular wire loop of radius 0.5 m lies in a plane perpendicular to a uniform magnetic field pointing from above into the plane of the loop, has a magnitude of 0.19 T. If in 0.15 s the wire is reshaped from a circle into a square, but remains in the same plane...

Homework Statement I recently made a direct current motor with a battery and a magnet. Is it possible for the coil to move in both directions without changing the current or magnetic field? If so, why might the motor work better in one direction? Homework Equations F= BIL The Attempt at a...

Homework Statement In this question , I am not convinced that δAD = δAC cos theta Homework EquationsThe Attempt at a Solution , i think it should be δAC = δAD cos theta , am i right ? I think so because we normally get the non-vertical and non -horizontal line and then cos the angle or...

https://www.ligo.caltech.edu/video/gravitational-waves How do gravitational waves get emitted here? Is it in a sphere or on a flat(?) surface?

Homework Statement A small block with mass 0.0400 kg is moving in the xy-plane. The net force on the block is described by the potential-energy function U(x, y) = (5.80 J/m2)x2-(3.60 J/m3)y3. What are the magnitude and direction of the acceleration of the block when it is at the point (x =...

Homework Statement Jane and her little brother John are fishing, sitting at opposite ends of a boat (Jane on the left, John on the right). Jane is having incredible luck! John, not so much. Jane offers to switch places in the boat with John. Jane has mass of 50 kg, john has a mass 30kg, and the...

I am trying to use two limit switches(this one) and two DPDT relays to control the direction of the motor. When the power is applied the motor should rotate one direction (direction for this question isn't important). Also, at this point (initialization) neither switch will be energized. The...

Hi there, I have a very basic maths problem that has highlighted a hole in my knowledge. I was answering the following question: The vertices of a triangle are A, B, C, with position vectors a, b, c . Show that the area of the triangle ABC is 1/2|b×c+c×a+a×b|. and got the answer as...

Homework Statement The diagram shows a uniform magnetic flux density B in the plane of the paper. Q and R mark the points where two long, straight and parallel wires carry the same current, I, in the same direction and perpendicular to the paper. The line through QR is at right angles to the...

Homework Statement The diagram shows a rigid conducting wire loop connected to a 6.0 V battery through a 6.0 V, 3.0 W lamp. The circuit is standing on a top-pan balance. A uniform horizontal magnetic field of strength 50 mT acts at right angles to the straight top part of the conducting wire in...

Homework Statement A current of 3 A flows down each of two long vertical wires, which are mounted side by side 5 cm apart. Show on a diagram the magnetic field pattern in a horizontal plane, indicating clearly the direction of the magnetic field at any point. What is the magnitude and direction...

Hi guys,If a particle is accelerating to the left, does this means the particle is decelerating to the right? And also does the sign change from negative to positive? Many Thanks.

Homework Statement the tensile force is applied at x direction to the cube , the cube will decrease in size in y and z direction , right ? according to notes, the strain in x direction εx = σxy/ E , where σy = normal stress in y direction , [/B]Homework EquationsThe Attempt at a Solution...

Homework Statement A stationary B nucleus decays into two alpha particles and a proton, and the speed of the proton is found to be 6.0x10^6 m/s. What is the magnitude and direction of the velocities of the alpha particles with respect to the proton? Homework Equations Unnecessary The Attempt...

If a sailing boat is running before the wind, i.e. with the wind exactly behind, is it possible for it to go faster than the wind? If one thinks of a wind generator on the boat it could perhaps operate an electric propulsion motor to give any desired speed? But what about the apparent wind when...

Hi! My high school physics tells me using right hand grip rule to determine the direction of magnetic field induced by a current carrying wire, but I wonder whether I can deduce the direction merely from Maxwell's Equations? Suppose now we have a current density in cylindrical...

In the figure below in e1 1.64 why is i(t) negative. When switch is put to S1 position, the capacitor will start discharging. So current will flow from top plate of capacitor to resistor to bottom plate of capacitor. Where did negative sign come from in eqn. 1.64? When charging the current...

Homework Statement ------------------ Homework Equations V=IR KCL/Node Voltage The Attempt at a Solution These are the solutions to some old homework assignments that my teacher posted, but I am very confused on the way he labeled his current flows in these problems. In the first picture...

Generally we use the left hand rule - (if index finger shows velocity, middle finger shows magnetic field, the thumb points towards force). Recently I also came across a left hand rule for lorentz force- Using your right-hand: point your index finger in the direction of the charge's velocity, v...

Having trouble researching/discovering any locking mechanisms that engage with force in a linear direction and then allow the engagement to be released with force in the same applied direction. I don't know if it has been done, any help/findings would be greatly appreciated. The only technology...

Homework Statement Hi everybody! I'm trying to solve a problem about dipoles, but there is something I don't quite get about it. Well, first here is the problem: An electric dipole ##\vec{p}_1## is placed at the zero-point and shows in the z-direction. A second electric dipole ##\vec{p}_2##...

I am trying to figure out how to calculate the boat velocity using wind speed and wind direction. I have tried to find sources online but this is the only useful site I managed to find: https://sites.google.com/site/yoavraz2/sailingboatspeedvs.windspeed Unfortunately it has been a while since I...

I am trying to find the direction of steepest ascent of this function with this given point: f(x) = x^2 - 4y^2 - 9 (1,-2) I have the understanding that the steepest ascent or in some cases descent can be measured by the gradient. So in wolfram alpha I type in: gradient f(x) = x^2 - 4y^2 - 9...

Homework Statement For the y-y axis buckling , the beam will bend towards either positive or negative y-axis , right ? I don't understand that why for y-y axis buckling , moment of inertia (Iy) about y-axis is used ? Homework EquationsThe Attempt at a Solution IMO , it's wrong ... When the...

If an observer accelerates through a simple vacuum, it is often said that they see Unruh radiation with acceleration of ##2.5*10^{20} m/s^2## equivalent to a temperature of 1K, but I haven't seen the polar distribution described, one might assume it was from 'ahead' of the direction of...

Hello all- I'm looking for some general advice and thought this would be a good forum. I fell in love with physics after my sophomore year of undergrad. As a Psychology major who hadn't even taken a math class since my junior year of high school, the Physics department cautioned me against...

This is the question: At a certain location in the Philippines, Earth’s magnetic field of 39 µT is horizontal and directed due north. Suppose the net field is zero exactly 8.0 cm above a long, straight, horizontal wire that carries a constant current. What are the magnitude and direction of the...

When a ball is bounced against a wall at an angle why is that the wall only applies a normal force perpendicular to the collision location? Shouldn't the force applied by the ball against the wall be along the line at which it travels, at an angle? Then by that logic, by Newton's 3rd Law...

I am just starting to learn about vectors and I have question regarding vectors and their parallel properties: Assume that we have two vectors A and B, and they are said to be parallel. We know that in order to be parallel the angle between the two vectors either have to be 0 or 180. However...

Homework Statement A particle undergoes three successive displacements given by ##S_1##=√2 m North- East, ##S_2##=2m due south and ##S_3##=4m 30 degree north of west , then find the magnitude of net displacement? Homework Equations ##S##= ##S_1## + ##S_2## + ##S_3## The Attempt at a Solution...

Hi, I've been lurking here for quite a bit for a while now (reading old threads, stickies, etc.). I figured it's time I finally make a PF account to join the community. A little about myself. I'm currently a 6yr student (I know...) at a medium size state university close to my home. I...

Hi, hopefully someone here can help me! I'm interested in Halbach Arrays and specifically I want to make a circular array in which the field is amplified away from the array (as in above or below it), not to its inner diameter (or exterior circumference). Is this possible? On the web I've seen...

Homework Statement In my book, I was told that when an element is subjected to pure shear stress, equalibrium required that equal shear stress must be developed on four sides of the element...these stresses must be direct toward or away from opposite corners of element.. Homework EquationsThe...

what is the direction of velocity observed by fish when man flying from air to water?

So, i was studying some fin design in a heat transfer course , and then came the part where the efficiency is to be calculated, then i noticed that when he calculated the surface area and the sides of a rectangular fin weren't included, so i searched and i found out that it was neglected...

Homework Statement I'm unsure of what exactly is changing the heat transfer direction in the triangular fin. Homework Equations $$q_{x} = -kA(x)\frac{dT(x)}{dx} (1)$$ $$q_{x+dx} = -kA(x)\frac{dT(x)}{dx} - k\frac{d}{dx}[A(x)\frac{dT(x)}{dx}] (2)$$ $$dq_{conv} = h(x)dS(x)P[T(x) - T_{∞}] (3)$$...

Homework Statement The magnitude of a force vector is 80.6 Newtons (N). The x component of this vector is directed along the +x axis and has a magnitude of 78.0 N. The y component points along the +y axis. (a) Find the angle between and the +x axis. (b) Find the component of along the +y...

What happens if a source and the observer move at the same direction? Always hear how only one of them doesnot move, or when they move towards each other. For example. An ambulance moves towards direction A with Va. A biker moves towards direction A as well, with Vb. What happens to the...

So I understand the with torque, T= r x F: r is a vector that points from axis to point of force, correct? I am confused about the direction of r is a couple of other circumstances, and I wanted to know if there is handy rule. For example a linear momentum, this diagram, does 'r' also point...

In high energy Z-pinch, lots of X-ray emit. Which direction is the highest density of photon radiation?

I just have a simple question to ask people of physics since I keep on forgetting to ask my physics teacher. Does changing your direction while in motion affect your velocity? If so why? What forces cause it's velocity to decrease. Assuming that friction is present.(Also would it affect an...

Homework Statement why does the moment -400Nm only act at region B and C? Why it doesn't act from A to C? http://imgur.com/a/5tfCg Homework Equations The Attempt at a Solution As we can see from figure, there's moment 400Nm on the beam at B at the top part and also the below part...

If a accelerated electron 10keV fly through a decelerating electric field that is set by 10KV high voltage, then after exit, the electron all kinetic energy is lost and become 0 velocity. Of course, braking radiation will happen. My question are: 1. what is the direction of radiation photon...

Homework Statement why for 0 <x <3 , why the author ignore the 10kN ? as we can see , the 10kN is located 3m from A ... 2nd question is , the author assume downwards force is positive , am i right ? Homework EquationsThe Attempt at a Solution for 0 <x <3 , the shearing force V = 4kN , as...