dissipative forces

(noun)

Forces that cause energy to be lost in a system undergoing motion.

Related Terms

Examples of dissipative forces in the following topics:

  • Problem Solving with Dissipative Forces

    • In the presence of dissipative forces, total mechanical energy changes by exactly the amount of work done by nonconservative forces (Wc).
    • Here we will adopt the strategy for problems with dissipative forces.
    • Since the work done by nonconservative (or dissipative) forces will irreversibly alter the energy of the system, the total mechanical energy (KE + PE) changes by exactly the amount of work done by nonconservative forces (Wc).
    • Therefore, using the new energy conservation relationship, we can apply the same problem-solving strategy as with the case of conservative forces.
    • Express the energy conservation relationship that can be applied to solve problems with dissipative forces

  • Arches of the Feet

    • The arches of the foot are formed by the tarsal and metatarsal bones; they dissipate impact forces and store energy for the subsequent step.
    • Strengthened by ligaments and tendons, the elastic properties of arches allow the foot to act as a spring, dissipating impact forces and storing energy to be transfered into the subsequent step improving locomotion.
    • Its weakest part (i.e., the part most liable to yield from overpressure) is the joint between the talus and navicular, but this portion is braced by the plantar calcaneonavicular ligament, a.k.a. spring ligament, which is elastic and is thus able to quickly restore the arch to its original condition when the disturbing force is removed.

  • Muscle Attachment Sites

    • At either end of the tendon its fibers intertwine with the fascia of a muscle or the periosteum, a dense fibrous covering, of a bone allowing for force to be dissipated across the bone or muscle.
    • Tendons mainly consists of closely packed collagen fibers running parallel to the force generated by the muscle they are attached to.

  • Period of a Mass on a Spring

    • The mass and the force constant are both given.
    • In one dimension, we can represent the direction of the force using a positive or negative sign, and since the force changes from positive to negative there must be a point in the middle where the force is zero.
    • The deformation of the ruler creates a force in the opposite direction, known as a restoring force.
    • It is then forced to the left, back through equilibrium, and the process is repeated until dissipative forces (e.g., friction) dampen the motion.
    • The force constant k is related to the rigidity (or stiffness) of a system—the larger the force constant, the greater the restoring force, and the stiffer the system.

  • Forced motion

    • Later we will see that it is no loss to treat sinusoidal forces; the linearity of the equations will let us build up the result for arbitrary forces by adding a bunch of sinusoids together.
    • The forcing function doesn't know anything about the natural frequency of the system and there is no reason why the forced oscillation of the mass will occur at $\omega_0$ .
    • In the first place the spring would stretch to the point of breaking; but also, dissipation, which we have neglected, would come into play.
    • The motion of the mass with no applied force is an example of a free oscillation.
    • Otherwise the oscillations are forced.

  • The energy method

    • Unfortunately, we're forced into this by the Newtonian strategy of specifying forces explicitly.
    • For systems in which energy conserved (no dissipation, also known as conservative systems), the force is the gradient of a potential energy function.
    • (The work done by a force in displacing a system from $a$ to $b$ is $\int _ a ^ b F ~dx$ .
    • Since energy is a scalar quantity it is almost always a lot easier to deal with than the force itself.
    • After all, force is a vector, while energy is always a scalar.

  • Mechanical Work and Electrical Energy

    • Mechanical work done by an external force to produce motional EMF is converted to heat energy; energy is conserved in the process.
    • As the rod moves and carries current i, it will feel the Lorentz force
    • Since the rod is moving at v, the power P delivered by the external force would be:
    • Note that this is exactly the power dissipated in the loop (= current $\times$ voltage).
    • More generally, mechanical work done by an external force to produce motional EMF is converted to heat energy.

  • Power

    • Power delivered to an RLC series AC circuit is dissipated by the resistance in the circuit, and is given as $P_{avg} = I_{rms} V_{rms} cos\phi$.
    • Power delivered to an RLC series AC circuit is dissipated by the resistance alone.
    • The inductor and capacitor have energy input and output, but do not dissipate energy out of the circuit.
    • The forced but damped motion of the wheel on the car spring is analogous to an RLC series AC circuit.
    • The shock absorber damps the motion and dissipates energy, analogous to the resistance in an RLC circuit.

  • Heat Conservation and Dissipation

    • Animals have processes that allow for heat conservation and dissipation in order to maintain a homeostatic internal body temperature.
    • Animals conserve or dissipate heat in a variety of ways.
    • However, vasoconstriction reduces blood flow in peripheral blood vessels, forcing blood toward the core and the vital organs found there, conserving heat .

  • Phase-Space Density

    • If there is no dissipation, the phase-space density along the trajectory of a particular particle is given by
    • where ${\bf F}$ is a force that accelerates the particles.
    • The requirement of no dissipation tells us that $\nabla_{\bf p} \cdot {\bf F} = 0$.