What is Jerk: Definition and 67 Discussions

A hypnic jerk, hypnagogic jerk, sleep start, sleep twitch, myoclonic jerk, or night start is a brief and sudden involuntary contraction of the muscles of the body which occurs when a person is beginning to fall asleep, often causing the person to jump and awaken suddenly for a moment. Hypnic jerks are one form of involuntary muscle twitches called myoclonus.
Physically, hypnic jerks resemble the "jump" experienced by a person when startled, sometimes accompanied by a falling sensation. Hypnic jerks are associated with a rapid heartbeat, quickened breathing, sweat, and sometimes "a peculiar sensory feeling of 'shock' or 'falling into the void'". It can also be accompanied by a vivid dream experience or hallucination. A higher occurrence is reported in people with irregular sleep schedules. Men have also been known to experience this at a higher rate than women. Moreover, when particularly frequent and severe, hypnic jerks have been reported as a cause of sleep-onset insomnia.Hypnic jerks are common physiological phenomena. Around 70% of people experience them at least once in their lives with 10% experiencing it daily. They are benign and do not cause any neurological sequelae.

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  1. Ahmed1029

    I Why are acceleration, jerk, etc not relative, just like velocity?

    I've been thinking about this for a while, and thought it would be nice if someone could guide me to an answer. In Newtonian mechanics, an inertial frame is coordinate system that's able to make measurements with respect to some imaginary axes attached to it. It's a well known fact that velocity...
  2. Arman777

    A What is the jerk parameter in terms of the Density parameters?

    In cosmology the deceleration parameter defined as the $$q_0 = \frac{1}{2}\sum_i\Omega_{i,0}(1+3w_i)$$ Is there a similar expression for the jerk parameter (##j_0##) ?
  3. S

    Velocity, acceleration, jerk, snap, crackle, pop, stop, drop, roll....

    Edit: I see this was discussed in the related thread sorry for a repost. If acceleration causes a change in velocity, and jerk causes a change in acceleration, snap causes a change in jerk, crackle causes a change in snap, pop causes a change in crackle, stop causes a change in pop, drop causes...
  4. W

    I Gravitational Jerk Computation

    I've seen much about jerk, and how it's generally nearly instantaneous, and for general acceleration, that's fine. However, if I lift at a constant acceleration upward slightly stronger than gravity is pulling me downward, the gravitation pull of the Earth will offset part of my force, so that...
  5. A

    I Is there any evidence of a universe expansion jerk

    As stated in the question--is there any evidence of a non zero rate of change of the acceleration of the expansion of the universe. What is the evidence for it and is it negative or positive? Also if there is what would it take to determine if there was a jounce?
  6. P

    Physics Experiment: Jerk & Inertia | Solving for dA/dt

    There is this experiment my high school teacher showed in physics class. You are probably aware of it (from practicalphysics.org) There is a video of a teacher actually doing the experiment here: https://sites.google.com/site/haatscience/physics/221-the-effect-of-inertia Gradually pull the...
  7. D

    Does acceleration go to zero instantaneously?

    Here's the scenario: If a force is accelerating an object at a constant rate, and force is removed, does the acceleration instantaneously go to zero? The problem i see with that is that on the graph, the acceleration line would be constant, horizontal, and then when the force is removed to...
  8. A

    I Questions About Acceleration and Jerk in Orbits

    In orbits it is said that ##\vec a \cdot \vec a' = |a||a'|## How is this possible? Two vectors multiply to get scalars, and yet we cannot do the dot product literally because we do not know either of the components of ##\vec a## or ##\vec a'##. Nor does the Angle Between Vectors Formula work...
  9. S

    Acceleration and jerk calculations

    I’m trying to calculate the theoretical jerk and acceleration curve/distance/time for an elevator. I have the constant starting jerk set to 1m/s3, constant acceleration set to 1m/s2 and full speed set to 1m/s. Looking at Wikipedia about both, I can work out the figures about acceleration but I...
  10. S

    When simple motion begins is there acceleration and jerk

    Ive been looking at the simple physics problems for 2D motion. For example, a ball starts from rest and is thrown at 5m/s at an angle of 30 degrees with respect to the ground on earth. Most of the problems assume that the acceleration in the x-direction is 0. Doesnt there need to be an initial...
  11. M

    Approach for determining jerk in a mechanical system

    Hello all, I require your expertise on building an approach or a framework to identify and measure the jerk or vibration in a mechanical system with a slider. What I have is a slider (S) with a vertical link (L1) attached to it and another horizontal link (L2) attached at the tip of the link...
  12. Ontophobe

    I What is the significance of the cosmological jerk in the expanding universe?

    The expansion of the universe is in a state of perpetual acceleration as evidenced by the cosmological redshift. But is there a jerk to this acceleration? Is the acceleration of the universe's expansion itself speeding up, staying the same, or slowing down?
  13. W

    Real world applications of Jerk and Cons. Acceleration?

    I did some light searching for Jerk and didn't find much, maybe I can be directed there if my question has been asked. I was tasked to find some real world differences between the two in my Dynamics class. It's not really homework, so I didn't post it there. I'm looking for a discussion from...
  14. C

    The TNB components of the jerk vector

    It can be found in any advanced calculus textbook the proof that, for a "well-behaved" space curve, the acceleration vector can be decomposed into components along the tangent and normal unit vectors. The acceleration vector is always orthogonal to the binormal vector. The decomposition is...
  15. Maria_Porto

    How do I calculate a "medium" jerk value of my motion data?

    I'm a psychologist and I'm currently studying physics but, because this is not my field of study, I'm having great difficulties. I am currently studying biological motion and I have to calculate the jerk of my 2D motion data and I don't even know where to start. My data is basically a bunch of...
  16. T

    Magnitude of radial component of jerk along line of centres

    Homework Statement Show that the component of the jerk along the line of centres of two gravitating bodies has magnitude 2G(m1+m2)r(dot)/r3. Homework Equations (Eq. 1) r(double dot) = - G(m1+m2)r(hat)/r2 (acceleration of body 2 relative to body 1) The Attempt at a Solution Sorry for the...
  17. Isaac0427

    Would a falling object have jerk?

    Hi guys! So I have been learning about jerk/jolt as the third time derivative of distance, and thinking about Newtons law of universal gravitation, and I have come to the conclusion that a falling object must have jerk, and even jounce. Here's how I came to that conclusion: The acceleration of a...
  18. T

    How Do You Calculate Jerk in Uniform Circular Motion?

    Homework Statement The question asks to calculate the jerk of an object (both its direction and magnitude) in uniform circular motion. Homework Equations j=d(a)/dt The Attempt at a Solution I know that the direction is opposite the velocity vector (I did this by drawing a circle and taking a...
  19. James Beck

    Jerk, Jounce, Snap, Crackle, Pop: What's the Motion?

    I read that the rate of change of acceleration is called Jerk, and the rate of change of Jerk is called Jounce. I guess sometimes these higher order derivatives are used when designing extremely precise equipment, like the Hubble or someone on this form said camshaft design. We can even talk...
  20. F

    Force of a full body jerk (myoclonic jerk)

    Hi there, I would like to know how much force a full body jerk creates. You've probably all experienced this, when you were just about to sleep in, when suddenly your whole body jerks. I know that it is probably very difficult to measure the force excactly. But what might be the probable range?
  21. Y

    How do I compute jerk in 2D space for a mouse tracking task?

    Hi everyone, I am a graduate student in psychology and am working on a research project where I am trying to derive the kinematics of a mouse tracking task. I am currently writing a MATLAB script to do this, and I believe my equations for velocity and acceleration are correct, but I have very...
  22. D

    We can perceive position, velocity, acceleration, jerk

    We can perceive position by establishing a reference point We can perceive velocity by noticing a change in position We can perceive acceleration by noticing a change in velocity We can perceive jerk by noticing a change in acceleration Can humans also perceive jounce or any higher order...
  23. M

    Best way to measure velocity, acceleration and jerk

    Hello, I have a one-dimensional path associated with timings, similar to: t0=0, x0=0 t1=0.1, x1=2 t2=0.2, x2=3 etc. Now I want to measure the velocity, acceleration and jerk at each time position. The first (and easy) way of doing this would be to loop through all points and compute...
  24. G

    What is Jerk and Jounce conceptually?

    Hello, I was doing some research on differentiating kinematics. For example, differentiating displacement will give you velocity, and differentiating velocity gives you acceleration. When you differentiate acceleration apparently you get something called "jerk" (wow what a jerk). And when you...
  25. D

    Jerk times velocity cross position

    The problem asked me to prove the following (where \vec{r}, \vec{v}, \vec{a} are the position, velocity and acceleration vectors of a moving particle): \frac{d}{dt} [\vec{a} \cdot (\vec{v} \times \vec{r})] = \dot{\vec{a}} \cdot (\vec{v} \times \vec{r}) I already did so, but my question...
  26. S

    Difference between jerk in accerlation and deceleration?

    Yes, I'm back to this Einstein jerk, but it's in an entirely different context. Please, mentors, do not close this until my problem is resolved. Okay, when one accelerates, one feels the Einstein jerk (discussed midway through his book). When one decelerates, one feels the Einstein "jerk"...
  27. S

    Does space have a physical role in the jerk of acceleration?

    Does space have a physical role in the "jerk" of acceleration? This "jerk" that the great Einstein talks about in his book is really confusing me. Without space, there seems not to be a medium through which matter can move, thusing allow it (matter) to make sense of "force." I'll use one...
  28. DiracPool

    Jerk: The Third Derivative of Position

    My physics world was stunned today. I've been studying classical physics for several years now and just came across the concept of "Jerk"--the derivative of acceleration or the third derivative of position. I initially thought it was a joke or some some "fringe force" concept, perhaps...
  29. R

    Robotics kinematics help, rotation, velocity, acceleration, jerk

    Homework Statement The question is: "The wheel kinematic constraints derived in section 3.2.3 of the book assume that the wheel does not skid (equation 3.12) or slide (equation 3.13). These assumptions are unrealistic in many situations, such as on the surface of Mars or on the DARPA Grand...
  30. M

    Why is jerk the change in acceleration over time?

    Recently I found out about jerk (or jolt). I've found that it represents the change in acceleration over time. To me, this makes no sense at all. To me, the change in acceleration is directly related to the radial distance between the two objects (if the forces acting on or imaginary objects are...
  31. K

    Are both velocity and jerk of charges responsible for magnetic fields?

    Are both velocity and "jerk" of charges responsible for magnetic fields? It is commonly believed that changes of electric fields cause contributions to a component of the magnetic field and that changes of magnetic fields cause contributions to a component of the electric field. In the case...
  32. N

    Jerk in Gravitation: Are Accelerations Equal in Cases of Varying Distances?

    Lets suppose that we setup two instances involving two masses m1 and m2. m1 > m2 Case 1. The two bodies are separated by a distance r = 20. Case 2. The two bodies are separated by a distance r = 10. Suppose that in both setups, we were to release all restraining forces on these two...
  33. Dembadon

    Why Does My Brain Question Me After Exams?

    :mad: :mad: :mad: Does this happen to anyone else?
  34. G

    How Does Constant Jerk Affect Projectile Motion in an Alternate Universe?

    Homework Statement In another universe, the force of gravity causes not a constant acceleration, but a constant "jerk" (third derivative of position with respect to time) with a value of j in the downward direction. An object is launched from the ground with an initial velocity of v_0 at an...
  35. G

    Surely Your Joking, MR.Feynman Being a Jerk

    In "Surely Your Joking MR.Feynman" chapter You Just Ask Them? There's a part with much contraverse, where he acts like a jerk to sleep with a girl. And it worked. He says "it was interesting to know that things worked much differently from how I was brought up." Why did it work?
  36. M

    Maximum jerk for experimental module

    Maximum "jerk" for experimental module 1. A landing module has a mass M with three springs each of stiffness k that hover over the surface (height not given). If the final touchdown velocity is to be Vtd, what is the maximum jerk (time rate change of acceleration) the module experiences given...
  37. B

    Jerk Equation: Calculating Profile from Speed Data

    Hi there, I time (seconds) and speed data for a journey in a car. I looking to get the jerk profile of the car. Jerk can be derived by taking the second derivative of the speed. Can some please show me an example of how to calculate it. Thank you Some sample data is time speed 1...
  38. Alpharup

    Can centripetal acceleration be called centripetal? jerk?

    Well I am now confused about centripetal acceleration. I have heard sometime ago that the change of acceleration is jerk. Let a body in centripetal acceleration change its velocity from 'v' to 'v1' in time 't'. The formula for centripetal acceleration is v^2/r. Let this acceleration be 'a'. Can...
  39. T

    Medical Knee Jerk Reaction: What is the Medical Term?

    What is the official medical term for this? I know there is one. Anybody care to explain it further?
  40. planethunter

    Jerk physics professor response

    I asked a professor for advice on whether he thought I would do well in his course given my limited coursework. This is his response: ” Dear Mr. ..., As a science student you should know that to establish a trend line you would need to provide many data points. With your expectation of an...
  41. X

    Vector jerk is the 3 derivative?

    Homework Statement r(t)=(5.00t2x + 12.5t3y meters The position r of a 12.0 kg mass, moving in the x-y plane Homework Equations Third derivative... sqrt(x2+y2) The Attempt at a Solution Is it correct to just take the third derivative and plug in 12 kg and find the magnitude...
  42. G

    Simulating motion in 1D with varying jerk?

    Hello, I am trying to accurately simulate motion in 1D with a jerk that is changing non-linearly, but predictably. As an arbitrary example, picture jerk increasing logarithmically over time. This is being done in the context of a physics simulation that is 'stepping' frame-by-frame (ie 60...
  43. D

    Dependence between jerk and acceleration

    Hello... I am using velocity, acceleration and jerk constraints to minimize feedrate speed of robot arm movement. I want to know if there is a way to compute maximum jerk if I have maximum velocity and acceleration. Any references would be helpful. Thanks Didi
  44. R

    Can you solve for delta d in jerk motion using this formula?

    What formula would one use to solve for delta d with regards to t, v1, a1, and constant J?
  45. J

    Change in acceleration (jerk) how to calculate

    Change in acceleration (jerk) how to calculate please help! im a grade 11 student and i got a question that i don't understand, here it is. 32) a) derive an equation for the change in acceleration by using a graph analysis technique on a a-t (acceleration vs time) graph. (note. The name given...
  46. D

    What is the Jerk Due to Gravity and How Can it be Calculated?

    I've been doing A LOT of brainstorming, algebra, and applying physics to a simple question that I simply can't find the answer to. If an object is in free-fall towards a fixed point of mass due to gravity then its acceleration at a given point of distance is GM/d^2 but this for some reason...
  47. P

    How to find the jerk of the acceleration of gravity?

    Good evening, The definition of jerk is change in acceleration with respect to time. So, we can define it as a derivative: \vec{j} = \frac{d\vec{a}}{dt} In absolute value: j = \frac{da}{dt} For most physics problems, the acceleration of gravity, g, is considered constant, since the height...
  48. W

    What is an equation for distance which relates the jerk and snap?

    Homework Statement Well I was perusing Wikipedia on physics and came across the "jerk" of an object, the rate of change of acceleration, as well as the "snap", the rate of change of the jerk. The units for these were \frac{m}{s^3} and \frac{m}{s^4} respectively. Is there some way to relate...
  49. H

    Finding an equation to represent a jerk

    hey everyone, The title of this thread explains what I'm trying to do. I want to find an equation that can represent a jerk. A jerk is a change in acceleration with respect to time. What I really want though is an equation for a jerk that doesn't have a time variable in it. I think I know the...
  50. O

    Clarifying the Jerk Four Vector: Definition & Form

    "jerk" 4-vector?? What is jerk four vector? and what is its definition or a form? as far as I know it is a rate of change of 4-acceleration. Could anyone clarify me?