Formulae – audio
Newton’s second law of motion 
F=ma 
Force equals mass multiplied by acceleration.


Linear momentum 
p=mv 
The linear momentum of a body equals the product of the mass of a body and its velocity.


Coulomb’s law 
F=k_{0} q_{1}q_{2}/r^{2} 
The electrostatic force acting simultaneously between two point charges is equal to the product of the proportionality constant k_{0}, the charges q_{1} and q_{2}, and the reciprocal of the square of the separation distance r of the point charges.

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Electric potential energy 
U=1/(4πε) q_{1}q_{2}/r 
The electric or electrostatic potential energy of charge q_{1} in the potential of charge q_{2} is equal to the product of the reciprocal of four pi multiplied by the permittivity ε of the medium, the charges q_{1} and q_{2}, and the reciprocal of the separation distance r of the point charges.

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Energy of a photon 
E=hf 
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.

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Momentum of a photon 
p=h/λ=E/c 
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.

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Heisenberg uncertainty principle 
(Δx)(Δp_{x})=h/(4π) 
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.

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Rest energy 
E_{0}=m_{0}c^{2} 
The total energy of a body at rest is equal to the product of its rest mass m_{0} (also called invariant mass) and the square of the speed of mass.

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Radioactive decay  N=N_{0}e^{λ}^{t} 
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 N_{0} (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.

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Halflife 
T_{1/2}=(ln2)/λ 
The halflife 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.

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