What is Position: Definition and 1000 Discussions

The missionary position or man-on-top position is a sex position in which, generally, a woman lies on her back and a man lies on top of her while they face each other and engage in vaginal intercourse. The position may also be used for other sexual activity, such as anal sex. It is commonly associated with heterosexual sexual activity, but is also used by same-sex couples.The missionary position is the most common sex position, but is not regarded as the most favoured one. It may involve sexual penetration or non-penetrative sex (for example, intercrural sex), and its penile-vaginal aspect is an example of ventro-ventral (front-to-front) reproductive activity. Variations of the position allow varying degrees of clitoral stimulation, depth of penetration, participation on the part of the woman, and the likelihood and speed of orgasm.
The missionary position is often preferred by couples who enjoy the romantic aspects of ample skin-to-skin contact and opportunities to look into each other's eyes and kiss and caress each other. The position is also believed to be a good position for reproduction. During sexual activity, the missionary position allows the man to control the rhythm and depth of pelvic thrusting. It is also possible for the woman to thrust against him by moving her hips or pushing her feet against the bed, or squeeze him closer with her arms or legs. The position is less suitable for late stages of pregnancy, or when it is desired for the woman to have greater control over rhythm and depth of penetration.

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  1. G

    Graph of Position Seems to be Wrong

    Homework Statement By relative velocity, we mean velocity with respect to a specified coordinate system. (The term velocity, alone, is understood to be relative to the observer’s coordinate system.) (a) A point is observed to have velocity Va relative to coordinate system A.What is its...
  2. astroman707

    Plot the position of the particle x=Acosbt

    Homework Statement The position of a particle as a function of time is given by x=Acosbt, where A and b are constants. The first question asks to roughly plot the position of the particle over the time interval (0,7) seconds. The second asks what time the particle passes the origin, and what...
  3. S

    Position from velocity time graph

    Homework Statement A particle starts from x_0 = 14m at t_0 = 0 and moves with the velocity graph shown What is the object's position at t = 2 s? Homework Equations Area under velocity time graph is the displacement of the particle. The Attempt at a Solution The part that confuses me is where...
  4. evinda

    MHB Will the balls meet at the same position?

    Hello! (Wave) At a clock (on which we have the positions $1,2, \dots, 12$) we place at position $1$ a blue ball and at position $2$ a red ball. At discrete times ($1,2,3, \dots$) we shift the two balls. Each time we shift the blue ball by three positions and the red ball by one position. Will...
  5. Felipe Lincoln

    Dependence of force on relative position and velocity

    I read that a force between two bodies can only depend on their relative position and relative velocity. But I can't understand in what is this statement leaning on and what it means.
  6. Aleoa

    I Probability density functions for velocity and position

    In the first volume of his lectures (cap. 6-5) Feynman asserts that these 2 can be the PDF of velocity and position of a particle. Under which conditions it's possible to model velocity and position of a particle using these particular PDFs ? ps: Is the "Heisenberg uncertainty principle"...
  7. I

    Why do position vectors have an arrow on top of them?

    According to the vector definition, the vectors have both the direction and magnitude such as displacement vectors which should possesses arrows on the top of them because they have displacement so they express a direction. On the other hand, position vectors are stationary, they do not have any...
  8. PGaccount

    B "We cannot measure both position and momentum...."

    [Mentors' note: This thread's prefix has been set to 'B'] We all know that the quote in the title is an imprecise convenience when talking about the Heisenberg uncertainty principle in a context where we would not want to enter into conceptual or fundamental issues to make a more correct...
  9. Cocoleia

    Position of particles on a detector after decay

    Homework Statement A hypertriton (a bound system with a L hyperon together with a deuteron core (proton and neutron) is produced at the origin of the coordinate, (x,y)=(0,0) with a velocity of 0.94c (beta=0.94), flying along the x-axis. The mass of the hypertriton is 2.991 GeV/c2 . It decays...
  10. WeiShan Ng

    I Distribution of Position in classical & quantum case

    I am confused about the difference between the two In Griffith's 2.3 The Harmonic Oscillator, he superimposes the quantum distribution and classical distribution and says What I understand for quantum case is that ##|\Psi_{100} (x)|^2## gives the probability we will measure the particle...
  11. J

    Measuring momentum using position wavefunction

    I was solving an exercise from Cohen's textbook, but then I got stuck in this question. "Let ψ(x,y,z) = ψ(r) the normalized wave function of a particle. Express in terms of ψ(r) the probability for: b) a measurement of the component Px of the momentum, to yield a result included between p1...
  12. F

    Charge on the capacitor after changing the switch position

    Homework Statement Homework Equations V = I R Q= CV The Attempt at a Solution When the switch is connected to position a : 20-106 * I = 0 ( KVL) Vc = 0 , because the switch is connected for a long time. I = 2*10-5 A When the switch is connected to position b : Q/(4*10-6) - 106 *2*10-5 = 0...
  13. P

    I Why do we need the position operator?

    As I understand it, |Ψ|2 gives us the probability density of the wavefunction, Ψ. And when we integrate it, we get the probability of finding the particle at whichever location we desire, as set by the limits of the integration. But when we use the position operator, we have integrand Ψ*xΨ dx...
  14. T

    Job Skills Need help getting back into a helpdesk position

    Hi, So there are very little Information Technology jobs around in my area according to indeed.com. I'm currently contributing to open source on GitHub (which is legally a job, but it's not a paid job). I'm really trying to get back into my field of computer science/information technology, but...
  15. sophiecentaur

    Stargazing What Causes the NEQ6 Pro Mount to Have 'Brain Failure' During Alignment?

    I have noticed a number of Skywatcher mounts in pictures posted on this thread so I guess there must be quite a few 'EQ' owners with loads of experience in these mounts. I know how to polar align and how to input location and time details. Also I often successfully do 3 star alignment and...
  16. jamalkoiyess

    Programs Does a Masters help me get a PhD position?

    Hello PF, So in my country (Lebanon), we have this French system of education where masters come after Bsc. and then you can consider the Ph.D. position. Apparently, this is not the case in the US and one can get into a graduate program with just the Bsc. I know they are equivalent but if...
  17. EF17xx

    AC generator -- Understanding coil voltages as function of position

    Homework Statement In an ac generator Voltage is maximum when the coil is parallel to the direction of magnetic field (B) Voltage is minimum (0) when the coil is perpendicular to the direction of magnetic field (B) I'm trying to understand why. Homework EquationsThe Attempt at a Solution A...
  18. T

    MHB Find position vector using midpoint of two other vectors

    Hi, I've got this problem I'm trying to work out. The problem seems simple, but I don't think I have a good way to construct a way to solve it. This is the problem. Let P and Q be two points with position vectors p and q and let R be a point midway between these two. Find an expression for the...
  19. D

    Expectation value of position

    Homework Statement Show that, for a general one-dimensional free-particle wave packet $$\psi (x,t) = (2 \pi h)^{-1/2} \int_{-\infty}^{\infty} exp [i (p_x x - p_x^2 t / 2 m)/h] \phi (p_x) dp_x$$ the expectation value <x> of the position coordinate satisfies the equation $$<x> = <x>_{t=t_0}...
  20. T

    Position of the front of an asteroid using special relativity

    Homework Statement I'm stuck on part (d) but I've included the previous subquestions in case they're useful. The length of an asteroid is exactly 300 m = 1 µls (micro light-second) when at rest. Draw a carefully labelled space-time diagram to illustrate the following: (a) Depict the rest...
  21. W

    Position mean in momentum-space (QM)

    Homework Statement Find ##\langle x \rangle## in the momentum representation I am having trouble understanding some of the steps needed to get to the expression, assistance is greatly appreciated! Homework Equations 3. The Attempt at a Solution [/B] $$\langle x \rangle = \langle \psi | x |...
  22. nmsurobert

    I Milky way arms and the position of the Earth

    I've been trying to understand why we see different milky way arms depending on where we are on Earth and what time of year it is. I've been googling and I can't find an answer. Can anyone explain this to me? If you have a picture handy that would really help. Thanks.
  23. Q

    Independence of Position and Velocity in Lagrangian Mechanics

    In Lagrangian mechanics, both q(t) and dq/dt are treated as independent parameters. Similarly, in Hamiltonian mechanics q and p are treated as independent. How is this justified, considering you can derive the generalized velocity from the q(t) by just taking a time derivative. Does it have...
  24. M

    Finding the position operator in momentum space

    Homework Statement Given ##\hat{x} =i \hbar \partial_p##, find the position operator in the position space. Calculate ##\int_{-\infty}^{\infty} \phi^*(p) \hat{x} \phi(p) dp ## by expanding the momentum wave functions through Fourier transforms. Use ##\delta(z) = \int_{\infty}^{\infty}\exp(izy)...
  25. I

    Wheatstone Bridge at Null position

    Homework Statement Consider the Wheatstone bridge as shown in the following figure, where ##e_0## is the Galvanometer reading. The condition for ##e_0 = 0 ## is called the null condition of the bridge. Using the Kirchhoff's rules, we can show that the condition is ## R_1R_4 = R_2 R_3##. Now I...
  26. renec112

    Harmonic oscillator - chance of of finding particle x>0

    Homework Statement A particle is moving in a 1-dimensional harmonic osciallator with the hamiltion: ## H = \hbar \omega (a_+ a_- + \frac{1}{2})## at time ## t=0## the normalized wave function is given by ## \Psi(x,0) = \frac{1}{\sqrt{2}}(\psi_0(x) + i\psi_1(x)) ## Task: Calculate for ## t \geq...
  27. AuxPart

    I Does the Schrödinger equation link position and momentum?

    I recently found this article about the dynamics of the wave function. It has some good simple illustrations and I found it valuable. But the author has a question himself, about understanding the Schrodinger equation. I wonder if anybody here could fill in the missing piece. The relevant part...
  28. Fia Ismi Nur Alfiah

    Mechanical Physics -- Find the velocity and acceleration of the particle from its position

    Homework Statement [/B] The position of a particle as a function of time is given by r(t) = i(1 - e^-kt ) + je^kt where k is a positive constant. Find the velocity and acceleration of the particle. Sketch its trajectory. Homework Equations v (t) = dr/dt a(t) = dv/dt The Attempt at a Solution...
  29. J

    Impulse from position time graph

    Homework Statement Homework EquationsThe Attempt at a Solution I think none of the options are correct . It is a uniform motion between t=0 and t=2 sec. Velocity is constant . Impulse is given by m∆v .Since ∆v = 0 , impulse is zero at t= 2 sec . Is that correct ?
  30. Aleberto69

    B Lag of a clock coming back to its initial position (Twins Paradox)

    Hello, I'm a beginner on SGR and I'm struggeling with this, probably, simple problem. I'm interested on exploring Field Theory ( relativistic) so I started reading http://www.elegio.it/mc2/LandauLifshitz_TheClassicalTheoryOfFields_text.pdf which was suggested and reccomended by a PF's member...
  31. Alain De Vos

    I What is the covariant derivative of the position vector?

    What is the covariant derivative of the position vector $\vec R$ in a general coordinate system? In which cases it is the same as the partial derivative ?
  32. physea

    Cloud Altitude: Understanding the Height Range of Clouds

    << Mentor Note -- poster has been reminded to do some reading on their own before asking simple questions at the PF >> Are clouds mostly in a specific height range from sea level? If yes, what is that height?
  33. H

    Find the forces on a table that is lifted in a tilted position

    Homework Statement Homework EquationsThe Attempt at a Solution what's the Fa and Fb? my logic is Fa = Wa - N = mg - ##\frac{N}{\cos \theta}## so is Fb... so the ratio is 1. But I know it's wrong. What will make the difference between Fa and Fb? can anyone give a clue please?
  34. C

    Engineering Mechatronics: DC Motor Position Control

    Homework Statement Write down the equations of motion and develop the continuous-time system. Homework Equations See my word doc. or PNG's. The Attempt at a Solution See my word doc. or PNG's. I assumed that there was no friction as no information was given. I can easily get the transfer...
  35. Ignitia

    How Can Two Point Charges Be Arranged to Nullify Electric Field at the Origin?

    Homework Statement "Can you arrange the two point charges q1 =−2.0×10−6 C and q2 =4.0×10−6 C along the x-axis so that E =0 at the origin?"Homework Equations E = K (|q|/r2) K = Coloumb Constant The Attempt at a Solution Since one particle is negatively charged and the other is positively...
  36. M

    How Do You Calculate Electric Field Strength and Direction?

    Homework Statement The diagram is attached. What is the strength of the electric field at the position indicated by the dot in Figure 1? What is the direction of the electric field at the position? Specify the direction as an angle measured clockwise from the positive x axis. Homework...
  37. LarryS

    I Why is position-space favored in QM?

    In non-relativistic QM, when one speaks of a "wave function" it is understood that one is referring to the position-space version of the wave function. Even if the observable being measured is other than position, like momentum or energy, the associated eigenfunctions are always from the...
  38. T

    How to find the position update for Step 2 in Spring Problem

    Homework Statement A spring has a relaxed length of 35 cm (0.35 m) and its spring stiffness is 10 N/m. You glue a 70 gram block (0.070 kg) to the top of the spring, and push the block down, compressing the spring so its total length is 12 cm. You make sure the block is at rest, then at time t =...
  39. T

    Derivative of (v)^2 with respect to position

    I forgot where I came across this and why I got so determined to figure it out but I wanted to ask about this d/dx(v^2) business. My question is to solidify my understanding of the chain rule with physics equations (sorry for crap terminology). Therefore, I know I use it and do the math as...
  40. Pushoam

    Calculating angle between velocity and position vector

    Homework Statement Homework EquationsThe Attempt at a Solution I took ## \frac { d\vec r}{dt} = 0 ## . This gives ##t_m = \frac { 1} {\sqrt{ 2}} ## ...(1) To calculate ## \alpha ## , ## \cos{ \alpha } = \frac { \vec v \cdot \vec r}{|\vec v||\vec r|} ## ...(2) Then, magnitude of...
  41. S

    A Can imaginary position operators explain real eigenvalues in quantum mechanics?

    Hello, some operators seem to "add up" and give real eigenvalues only if they are applied on the imaginary position, ix, rather than the normal position operator, x, in the integral : \begin{equation} \langle Bx, x\rangle \end{equation} when replaced by:\begin{equation} \langle Bix...
  42. A

    A Transformation of position operator under rotations

    In the momentum representation, the position operator acts on the wavefunction as 1) ##X_i = i\frac{\partial}{\partial p_i}## Now we want under rotations $U(R)$ the position operator to transform as ##U(R)^{-1}\mathbf{X}U(R) = R\mathbf{X}## How does one show that the position operator as...
  43. M

    Convergent lenses and calculating image position

    Homework Statement Two convergent lens are identical in focal length (f=10cm) and the oobject height (h0) is 3.5 cm. The distance between the two lenses is 30cm and the distance from the object to the first lens is 30cm. -Draw a diagram on the figure and show the image position (di) and size...
  44. F

    I Measurement of a particle's position using photons

    I've read that a particle's position can be measured by firing a photon at it, but how does one actually determine the position of the particle by doing this? What is the maths behind it (is it calculated from momentum conservation)? Furthermore, I've read that increasing the energy of the...
  45. shihab-kol

    B Why is the asteroid belt located between Mars and Jupiter?

    The asteroid belt is present between Mars and Jupiter but why is it spaced out like that? Why not between some other planets?
  46. S

    How Do You Calculate Velocity and Acceleration from a Position Vector?

    Homework Statement The position vector of an object of mass 0.10 kg at time t in seconds is given by =(^3+5)−4+2^2 Find the velocity and the acceleration as a function of t Homework Equations =(^3+5)−4+2^2 The Attempt at a Solution For velocity I think the equation needs to be...
  47. C

    Expressing y(t) including the effects of air resistance & gravity

    Homework Statement [/B] Hi everyone! So I've got this similar problem as I posted yesterday, but this one is slightly different due to the presence of gravity: A particle in gravitational field ##~~g## starts traveling upward (positive direction) along the y-axis from ##~~y=0## with the...
  48. F

    Instantaneous velocity calculation from position data

    Hello Forum, Given position and related time data, what is the most correct way to calculate the instantaneous speed? For example, given the data (x1, t1) , (x2, t2), (x3, t3) , (x4, t4), (x5, t5), is the instantaneous speed at time t3 given more correctly by v(t_3) = \frac{(x_4-x_2)}...
  49. L

    Finding Velocity and Acceleration based on position of X & Y

    1. Homework Statement Given x and y position ... find magnitude of both velocity and acceleration and their direction at t = 2 ? x = 4t y = 30 - 2.2t^2 would the velocity's magnitude be sqrt(8^2 + 8.8^2) ? Homework Equations v = sqrt(vy^2 + vx^2) The Attempt at a Solution vy = -8.8 vx= 8...
  50. F

    Admissions Applying for a PhD position in Germany/Sweden/Ireland

    I have a masters degree in physics and I want to apply for a PhD position especially in Germany. What are the necessary steps that I should take and how can I apply for a scholarship? I have looked online but some information are a bit confusing and lacking so I hope someone could layout a rough...
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