Force equals mass multiplied by acceleration.

The linear momentum of a body equals the product of the mass of a body and its velocity.

The electrostatic force acting simultaneously between two point charges is equal to the product of the proportionality constant k₀, the charges q₁ and q₂, and the reciprocal of the square of the separation distance r of the point charges.

The electric or electrostatic potential energy of charge q₁ in the potential of charge q₂ is equal to the product of the reciprocal of four pi multiplied by the permittivity ε of the medium, the charges q₁ and q₂, and the reciprocal of the separation distance r of the point charges.

The energy of a photon is equal to the product of the Planck’s constant h and the frequency f of its associated electromagnetic wave.

The momentum of a photon is equal to the ratio of the Planck’s constant h to the wavelength m of its associated electromagnetic wave, or the ratio of its energy E to the speed of light.

In describing an elementary particle, the uncertainty in the position (Δx) multiplied by the uncertainty in its momentum (Δp_x) is equal to Planck’s constant divided by four pi.

The total energy of a body at rest is equal to the product of its rest mass m₀ (also called invariant mass) and the square of the speed of mass.

For a given sample of a specific radioisotope, the number of atoms present after a period of time t is equal to the initial number of atoms N₀ (at time t = 0) multiplied by the exponential function of –λt, where λ is the decay constant for the radioisotope and t is the elapsed time.

T_1/2=(ln2)/λ
 

The half-life of a substance undergoing decay, i.e. the period of time in which the expected number of entities that have decayed is equal to half the original number, is equal to the natural logarithm of two divided by the decay constant λ for the substance; λ being a positive number.