Energy of a Single Particle

Introduction

In the previous sections, we have been learning about applying the Energy Principal in situations you may encounter in real life; a baseball is thrown, a moon orbits around a planet, two cars crash into one another. But now, we are going to look at something a bit more removed, but even more fundamental.

Single particles have energy associated with them. Calculating this energy is a lot like calculating the energy of bigger particles, but with something called a relativistic correction factor. This is notated with a "γ" (gamma) and is sometimes called the "Lorentz Factor". Exactly why this factor is needed can get into an explanation a bit beyond the scope of this course, but very basically, particles behave a bit differently when traveling near the speed of light.

That said, there are two types of energy a particle can have: rest energy and kinetic energy. Rest energy is, as you might expect, the energy of the rest mass of a particle. Kinetic energy, as we have seen before, is the energy associated with the motion of a particle. Calculations associated with these energies are usually very simple, so pay attention to the equations and units and you should be fine.

A Mathematical Model

Types of point particles:

1. Electrons
2. Protons
3. Neutrons

Masses of point particles:

1. Electron mass = 9.109 e -31 kg
2. Proton mass = 1.6726 e -27 kg
3. Neutron mass = 1.6750 e -27 kg

There are three equations to look at that were discussed above:

(1) Relativistic Correction Factor

[math]\displaystyle{ γ = \sqrt{1-(v/c)} }[/math] where v is the velocity of the particle and c is the speed of light

(2) Rest Energy of a particle

[math]\displaystyle{ E_{Rest}=mc^2 }[/math] - Rest Energy, where m is the mass and c is the speed of light. This type of energy describes the inherent energy contained within an object arising from chemical makeup. Rest energy will only ever change if the system being observed is at an atomic level where particles tends to change identities spontaneously during interactions with surroundings.

(3) Kinetic Energy of a particle nearing the speed of light

[math]\displaystyle{ E_{Kinetic}=γmc^2-mc^2 }[/math] - Where γ is as calculated above, m is the mass of the particle and c is the speed of light

(4) The combined energy equation
[math]\displaystyle{ E_{Particle}=γmc^2 }[/math]
Where γ is as calculated above, m is the mass of the particle and c is the speed of light

A Computational Model

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Examples

A proton moves at 0.950c. Calculate its (a) rest energy, (b) total energy, and (c) kinetic energy.

(a) [math]\displaystyle{ E_{rest}=mc^2 }[/math] = (1.67e-27 kg)(3e8 m/s)^2 = 1.5e-10 J
(b) [math]\displaystyle{ E_{particle}=γmc^2 }[/math] = (1.5e-10 J)/((1-(0.950c/c)^2)^(1/2)) = 4.81e-10 J
(c) [math]\displaystyle{ K=γmc^2-mc^2 }[/math] = 4.81e-10 J - 1.50e-10 J = 3.31e-10 J

Connectedness

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History

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