rest mass

(noun)

the mass of a body when it is not moving relative to an observer

Related Terms

Examples of rest mass in the following topics:

  • Relativistic Kinetic Energy

    • Relativistic kinetic energy can be expressed as: $E_{k} = \frac{mc^{2}}{\sqrt{1 - (v/c)^{2})}} - mc^{2}$ where $m$ is rest mass, $v$ is velocity, $c$ is speed of light.
    • Using $m$ for rest mass, $v$ and $\nu$ for the object's velocity and speed respectively, and $c$ for the speed of light in vacuum, the relativistic expression for linear momentum is:
    • The body at rest must have energy content equal to:
    • $KE = mc^2-m_0c^2$, where m is the relativistic mass of the object and m0 is the rest mass of the object.
    • Thus, the total energy can be partitioned into the energy of the rest mass plus the traditional classical kinetic energy at low speeds.

  • Relativistic Energy and Mass

    • Relativistic mass was defined by Richard C.
    • For a slower than light particle, a particle with a nonzero rest mass, the formula becomes where is the rest mass and is the Lorentz factor.
    • When the relative velocity is zero, is simply equal to 1, and the relativistic mass is reduced to the rest mass.
    • In the formula for momentum the mass that occurs is the relativistic mass.
    • Relativistic energy ($E_{r} = \sqrt{(m_{0}c^{2})^{2} + (pc)^{^{2}}}$) is connected with rest mass via the following equation: $m = \frac{\sqrt{(E^{2} - (pc)^{^{2}}}}{c^{2}}$.

  • Energy, Mass, and Momentum of Photon

    • It has no rest mass and has no electric charge.
    • Momentum of photon: According to the theory of Special Relativity, energy and momentum (p) of a particle with rest mass m has the following relationship: $E^2 = (mc^2)^2+p^2c^2$, where c is the speed of light.
    • In the case of a photon with zero rest mass, we get $E = pc$.
    • You may wonder how an object with zero rest mass can have nonzero momentum.

  • Relativistic Shocks

    • It is most clear to use the rest-mass energy density for $n_\mathrm{prop}$.
    • where $w=\epsilon + p$ and $\epsilon$ includes the rest-mass energy of the particles.
    • Here $w$ is the enthalpy per unit volume whereas in previous sections it denoted the enthalpy per unit mass, $w_\mathrm{mass}=w_\mathrm{volume} V$.
    • The first term cancels in the previous equation, leaving the middle term which equals twice the enthalpy per unit mass.

  • Photon Interactions and Pair Production

    • ., the total rest mass energy of the two particles) and that the situation allows both energy and momentum to be conserved.
    • The energy of this photon can be converted into mass through Einstein's equation $E=mc^2$ where $E$ is energy, $m$ is mass and $c$ is the speed of light.
    • The photon must have enough energy to create the mass of an electron plus a positron.
    • The mass of an electron is $9.11 \cdot 10^{-31}$ kg (equivalent to 0.511 MeV in energy), the same as a positron.

  • Normal Forces

    • A more complex example of a situation in which a normal force exists is when a mass rests on an inclined plane.
    • In this case, the normal force is not in the exact opposite direction as the force due to the weight of the mass.
    • This is because the mass contacts the surface at an angle.
    • A mass rests on an inclined plane that is at an angle $\theta$ to the horizontal.
    • The following forces act on the mass: the weight of the mass ($m \cdot g$),the force due to friction ($F_r$),and the normal force ($F_n$).

  • Rocket Propulsion, Changing Mass, and Momentum

    • The remainder of the mass (m−m) now has a greater velocity (v+Δv).
    • The third factor is the mass m of the rocket.
    • It can be shown that, in the absence of air resistance and neglecting gravity, the final velocity of a one-stage rocket initially at rest is
    • If we start from rest, the change in velocity equals the final velocity. )
    • (a) This rocket has a mass m and an upward velocity v.

  • Relationship Between Torque and Angular Acceleration

    • Just like Newton's Second Law, which is force is equal to the mass times the acceleration, torque obeys a similar law.
    • If you replace torque with force and rotational inertia with mass and angular acceleration with linear acceleration, you get Newton's Second Law back out.
    • If no outside forces act on an object, an object in motion remains in motion and an object at rest remains at rest.
    • With rotating objects, we can say that unless an outside torque is applied, a rotating object will stay rotating and an object at rest will not begin rotating.

  • Period of a Mass on a Spring

    • The mass and the force constant are both given.
    • This is the equilibrium point, where the object would stay at rest if it was released at rest.
    • These forces remove mechanical energy from the system, gradually reducing the motion until the ruler comes to rest .
    • The greater the mass of the object is, the greater the period T.
    • (c) The mass's momentum has carried it to its maximum displacement to the right.

  • The First Law: Inertia

    • According to this law, a body at rest tends to stay at rest, and a body in motion tends to stay in motion, unless acted on by a net external force.
    • The acceleration of an object is parallel and directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object.
    • If you haven't heard it in the form written above, you have probably heard that "a body in motion stays in motion, and a body at rest stays at rest."
    • Inertia is the property of a body to remain at rest or to remain in motion with constant velocity.
    • Some objects have more inertia than others because the inertia of an object is equivalent to its mass.