axis

(noun)

An imaginary line around which an object spins or is symmetrically arranged.

Related Terms

Examples of axis in the following topics:

  • Two-Component Forces

    • Consider an object moving along the x-axis.
    • If no net force is applied to the object along the x-axis, it will continue to move along the x-axis at a constant velocity, with no acceleration .
    • We can easily extend this rule to the y-axis.
    • If the resultant moment about a particular axis is zero, the object will have no rotational acceleration about the axis.
    • Again, we can extend this to moments about the y-axis as well.

  • Torque

    • ., the tendency of a force to rotate an object about an axis).
    • In the case of rotation, torque is defined with respect to an axis such that vector "r" is constrained as perpendicular to the axis of rotation.
    • In other words, the plane of motion is perpendicular to the axis of rotation.
    • Since torque depends on both the force and the distance from the axis of rotation, the SI units of torque are newton-meters.

  • Moment of Inertia

    • Moment of inertia also depends on the axis about which you rotate an object.
    • Objects will usually rotate about their center of mass, but can be made to rotate about any axis.
    • The moment of inertia in the case of rotation about a different axis other than the center of mass is given by the parallel axis theorem.
    • Net τ is the total torque from all forces relative to a chosen axis.
    • This equation is actually valid for any torque, applied to any object, and relative to any axis.

  • Angular Quantities as Vectors

    • The axis of rotation of a rotating wheel is the only place that has a fixed direction.
    • The direction of angular momentum and velocity can be determined along this axis.
    • Imagine the axis of rotation as a pole through the center of a wheel.
    • From a spinning disc, for example, let's again imagine a pole through the center of the disc, at the axis of rotation.
    • In addition, your thumb is pointing straight out in the axis, perpendicular to your other fingers (or parallel to the 'pole' at the axis of rotation).

  • Inelastic Collisions in Multiple Dimensions

    • where $v_1$ is the initial velocity of the first mass, $v{}'_1$ is the final velocity of the first mass, $v_2$is the initial velocity of the second mass, and $\theta{}'_1$ is the angle between the velocity vector of the first mass and the x-axis.
    • The components of velocities along the x-axis have the form $v \cdot cos \theta$, where θ is the angle between the velocity vector of the mass of interest and the x-axis.
    • The components of velocities along the y-axis have the form v \cdot sin θ, where θ is the angle between the velocity vector of the mass of interest and the x-axis.

  • Refraction Through Lenses

    • The convex lens is shaped so that all light rays that enter it parallel to its axis cross one another at a single point on the opposite side of the lens.
    • The axis is defined as a line normal to the lens at its center (as shown in ).
    • Due to the lens's shape, light is thus bent toward the axis at both surfaces.
    • shows the effect of a concave lens on rays of light entering it parallel to its axis (the path taken by ray 2 in the figure is the axis of the lens).
    • The concave lens is a diverging lens, because it causes the light rays to bend away (diverge) from its axis.

  • Thin Lenses and Ray Tracing

    • A ray entering a diverging lens parallel to its axis seems to come from the focal point F.
    • A ray entering a converging lens through its focal point exits parallel to its axis.
    • A ray that enters a diverging lens by heading toward the focal point on the opposite side exits parallel to the axis.
    • Rays of light entering a diverging lens parallel to its axis are diverged, and all appear to originate at its focal point F.
    • Rays of light entering a converging lens parallel to its axis converge at its focal point F.

  • Components of a Vector

    • Vectors are geometric representations of magnitude and direction which are often represented by straight arrows, starting at one point on a coordinate axis and ending at a different point.
    • Next, draw a straight line from the origin along the x-axis until the line is even with the tip of the original vector.
    • The vertical component stretches from the x-axis to the most vertical point on the vector.

  • Relationship Between Torque and Angular Acceleration

    • In fact, this equation is Newton's second law applied to a system of particles in rotation about a given axis.
    • The net torque about an axis of rotation is equal to the product of the rotational inertia about that axis and the angular acceleration, as shown in Figure 1 .

  • Rotational Angle and Angular Velocity

    • When an object rotates about an axis, as with a tire on a car or a record on a turntable, the motion can be described in two ways.
    • When the axis of rotation is perpendicular to the position vector, the angular velocity may be calculated by taking the linear velocity $v$ of a point on the edge of the rotating object and dividing by the radius .
    • The angular velocity describes the speed of rotation and the orientation of the instantaneous axis about which the rotation occurs.
    • The direction of the angular velocity will be along the axis of rotation.