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. Cyrus

    Beep beep, out of my way you jerk

    http://www.google.com/hostednews/afp/article/ALeqM5izGwd4isLu8fchZCXFyGXO7BhK6A https://www.youtube.com/watch?v=lxyMzR9K1Dk Bad assssssssss [url]AGaEHd1QTuI&NR=1[/youtube]
  2. K

    Learn to be a Jerk - Desperate for Change

    Seriously, this is not a joke. I'm too nice and it gets me nowhere. Consider this... The cable guy today knocked down my $2000 flat screen TV. My mom was bitching at him and told him he or his company was going to pay for it. So me and him went outside to discuss it. I could see the...
  3. T

    Postion -> Velocity -> Acceleration -> Jerk ->?

    We all know that, assuming x(t) = position as a function of time, then: x'(t) = v(t) = velocity x''(t) = v'(t) = a(t) = acceleration x'''(t) = v''(t) = a'(t) = j(t) = jerk (assuming j is the symbol for jerk). But what does x''''(t) = j'(t) come out to be? Is there a fourth derivative of...
  4. E

    What is the jerk of a falling object?

    Suppose an object is suspended above the Earth, then released. It immediately accelerates to 32.2 f/s^2. There should be a jerk as the acceleration changes. Is there an experimental method to measure that jerk? Experimental as opposed to just doing the math. Thanks.
  5. M

    Deriving the Gravitational Jerk Equation and Solving for Time and Position

    Is anyone aware of a function expressesing position (separation) in terms of time, s=f(x), given only acceleration due to the force of gravity. I am aware of the Gravitational Jerk Equation J= \frac{2Gm}{s^{3}} \frac{ds}{dt} where m=mass of attracting object G = gravitational constant But...
  6. ~christina~

    Deriving the rate time equation for a Jerk (J)

    Homework Statement Automotive engineers refer to the time rate change of acceleration as the Jerk. Assuem an object moves in 1 dimention such that it's Jerk is constant. a) determine expressions for it's 1. acceleration ax(t) 2. velocity vx(t) 3. position x(t) given initial...
  7. S

    Does Attraction to Weight Influence Superficiality?

    My gf recently lost weight and is now down to 103 lbs. I find myself more attracted to her than before. I'm sorry, but I just like skinny. I find skinny girls so much more attractive than non-skinny girls. Does this make me superficial?
  8. Andrew Mason

    News What a jerk (cont'd from General Physics)

    [mentor's note: the following posts were split off a thread in General Physics: https://www.physicsforums.com/showthread.php?t=155149 ] The only one that comes to mind is the GWB force. It was thought to be of relatively short duration but has demonstrated a much longer lasting effect. The...
  9. J

    Is Constant Jerk a Real Physical Situation?

    I asked a quesion about this a while back, but I never felt that I got a perfectly straight answer. I want to know if there is any real physical situation where there is a constant jerk (third derivative of displacement with respect to time). I am perfectly aware of how common jerk is as well...
  10. J

    Questions on Jerk: What Occurs in Nature?

    Questions on the "jerk" I have two questions relating to the third derivative of displacement with respect to time. My main question is this. Does a jerk ever occur in the natural universe? I know that there are many situations in which acceleration changes over time, but all that I can...
  11. C

    Ballistics, trajectory and jerk.

    Could the rate of change of accelaration (or jerk in m/s3) affect the trajectory of a projectile? If so could it be to a noticeable extent? Given two systems where projectiles are fired by different propellants, say gasses with different rates of expansion. One reaches its maximum velocity...
  12. A

    "Exploring the Meaning of 'Jerk': What Is It?

    What is Jerk? I have a rough idea of what it is, but I would like to know more.
  13. I

    What is meant by jerk and how it can be measured

    dear sir i want to know clearly about jerk and it's measurement. what i undersatnd is jerk means rate of change of acceleration. if it is measred in terms of g then plot against time. i want to konw is there is any instrument is there to measure it. thanking you
  14. Loren Booda

    The jerk from your college/workplace who made it big

    The jerk from your college/workplace who "made it big" Doesn't it irk you when an dishonorable, petty person you know from your alma mater/business achieves "success"? I believe in forgiveness, but I also nourish grievances to those who are overrated and have never suffered. Give below a...
  15. S

    Experiencing Newton's Law: Why Do Passengers Jerk Forward?

    Not sure exactly: 1. Why do passengers jerk forward when the car suddenly stops? I know it is somethin' relative to Newton's law but I don't know which law it is and how it actually happens. and 2. Why do the passengers feel like they are pushed to the outside of a turn.
  16. M

    Transitions from Rest State to Rectilinear Motion: Infinite Jerk?

    Anyone- From long ago IIRC a body that transitions from a rest state to a rectilinear moving state undergoes nearly infinite jerk (change in 'a'). On the one hand, my memory is reinforced by the idea that not all functions have infinitely many derivatives... But on the other hand, I may not...
  17. K

    Jerk of the point of contact of a ball rolling on a flat surface

    Hi, I'm working on a kinematics problem of rolling a golf ball on a flat plane (4-position infinitesimally separated solution). The solution sought is to be planar, so we're working in 2D only. This is largely irrelevant though, as I'm facing a rather undergraduate puzzler. I need to...
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