helical motion

(noun)

The motion that is produced when one component of the velocity is constant in magnitude and direction (i.e., straight-line motion) while the other component is constant in speed but uniformly varies in direction (i.e., circular motion). It is the superposition of straight-line and circular motion.

Related Terms

Examples of helical motion in the following topics:

  • Helical Motion

    • Helical motion results when the velocity vector is not perpendicular to the magnetic field vector.
    • In the section on circular motion we described the motion of a charged particle with the magnetic field vector aligned perpendicular to the velocity of the particle.
    • This produces helical motion (i.e., spiral motion) rather than a circular motion.
    • Uniform circular motion results.
    • Describe conditions that lead to the helical motion of a charged particle in the magnetic field

  • Direction of the Magnetic Force: The Right Hand Rule

    • Because the force is always perpendicular to the velocity vector, a pure magnetic field will not accelerate a charged particle in a single direction, however will produce circular or helical motion (a concept explored in more detail in future sections).

  • Springs

    • Neglecting frictional forces, Mechanical energy conservation demands that, at any point during its motion,$\begin{aligned} Total ~Energy &= \frac{1}{2} m v^2 + \frac{1}{2}k x^2 \\ &= \frac{1}{2} k x_f^2 = constant.
    • Plot of applied force F vs. elongation X for a helical spring according to Hooke's law (solid line) and what the actual plot might look like (dashed line).

  • Electric vs. Magnetic Forces

    • Force due to both electric and magnetic forces will influence the motion of charged particles.
    • The angle dependence of the magnetic field also causes charged particles to move perpendicular to the magnetic field lines in a circular or helical fashion, while a particle in an electric field will move in a straight line along an electric field line.
    • A further difference between magnetic and electric forces is that magnetic fields do not net work, since the particle motion is circular and therefore ends up in the same place.
    • We mentioned briefly above that the motion of charged particles relative to the field lines differs depending on whether one is dealing with electric or magnetic fields.

  • Chemotaxis

    • By repeatedly evaluating their course, and adjusting if they are moving in the wrong direction, bacteria can direct their motion to find favorable locations with high concentrations of attractants (usually food) and avoid repellents (usually poisons).
    • In the presence of a chemical gradient bacteria will chemotax, or direct their overall motion based on the gradient.
    • The helical nature of the individual flagellar filament is critical for this movement to occur.

  • Perceiving Motion

    • Motion perception happens in two ways that are generally referred to as first-order motion perception and second-order motion perception.
    • First-order motion perception occurs through specialized neurons located in the retina, which track motion through luminance.
    • However, this type of motion perception is limited.
    • One advantage to feature-tracking is that motion can be separated both by motion and by blank intervals where no motion is occurring.
    • Visual illusions offer insight into how motion is perceived.

  • Defining Kinematics

    • Kinematics is the study of the motion of points, objects, and groups of objects without considering the causes of its motion.
    • Kinematics is the branch of classical mechanics that describes the motion of points, objects and systems of groups of objects, without reference to the causes of motion (i.e., forces).
    • The study of kinematics is often referred to as the "geometry of motion."
    • Objects are in motion all around us.
    • The word "kinematics" comes from a Greek word "kinesis" meaning motion, and is related to other English words such as "cinema" (movies) and "kinesiology" (the study of human motion).

  • Supercoiling

    • In a "relaxed" double-helical segment of B-DNA, the two strands twist around the helical axis once every 10.4 to 10.5 base pairs of sequence.
    • The simple figure eight is the simplest supercoil, and is the shape a circular DNA assumes to accommodate one too many or one too few helical twists.
    • For each additional helical twist being accommodated, the lobes will show one more rotation about their axis.
    • Extra helical twists are positive and lead to positive supercoiling, while subtractive twisting causes negative supercoiling.
    • Note that the helical nature of the DNA duplex is omitted for clarity.

  • Virus Classification

    • Capsids are classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex .
    • For example, the tobacco mosaic virus has a naked helical capsid .
    • (a) Rabies virus has a single-stranded RNA (ssRNA) core and an enveloped helical capsid, whereas (b) variola virus, the causative agent of smallpox, has a double-stranded DNA (dsDNA) core and a complex capsid.
    • Viruses can also be classified by the design of their capsids which are classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex.
    • The capsid of the (a) polio virus is naked icosahedral; (b) the Epstein-Barr virus capsid is enveloped icosahedral; (c) the mumps virus capsid is an enveloped helix; (d) the tobacco mosaic virus capsid is naked helical; and (e) the herpesvirus capsid is complex.

  • Types of Motion

    • There are four types of contrapuntal motion between two musical lines.
    • In parallel motion, two voices move in the same direction by the same generic interval.
    • This will always be true when two voices move in parallel motion.
    • In similar motion, also called direct motion, two voices move in the same direction, but by different intervals.
    • This will always be the case with similar or direct motion.