1. Nuclear Force and Particles
Principles of Physics

2. Models of the Atom
Understanding of wave-particle duality led to better understanding of the atom It was determined that the protons and neutrons occur together in the center with electrons orbiting it at various locations But, how does the nucleus stay together when it is made up of like and neutral charges???

3. Nuclear Forces
Strong Force: – attractive force between particles in nucleus
Keeps nucleus stable
100 x stronger than the electrostatic force
only effective at small distances (short range)
breaking “bonds” – releases a lot of energy

4. Nuclear Force Weak force: responsible for the radioactive decay
Weaker than strong and electromagnetic forces
For large atoms the strong force is not always strong enough to hold the nucleus together
The weak force breaks the atom into smaller more stable atoms while releasing energy
The weak force is responsible for such things as the sun being able to produce energy and carbon dating

5. Einstein’s Mass-Energy Equation
Mass is another form of energy.
To find the mass equivalent of energy we use Einstein’s famous equation:
E=mc2   
E = energy (J)
m = mass (kg)
c = speed of light in a vacuum = 300,000,000 m/s

6. Mass-Energy Conversions
Example: Energy from the sun is produced through radioactive decay. The sun’s mass is being converted into energy. As the Sun’s energy comes to Earth , it’s mass will continue to decrease. Example: During chemical reactions when atoms combine the sum of the mass of the individual atoms before the reaction is not equal to the mass of the combined atoms after the reaction. The excess mass was converted to energy.

7. Fission
Fission: splitting of large atoms resulting in the release of energy
The energy released is related to the mass lost through E= mc2
Fission can occur as a chain reaction
Atomic bomb
Nuclear reactors

8. Fusion
Fusion: Combining of small atoms to make larger ones and a release of energy
The energy released is related to the mass lost through E= mc2
Fusion requires a huge amount of energy to activate
The sun and stars produce energy through fusion
No successful fusion reactors exist on Earth, because of the conditions necessary to activate the reaction

9. Elementary Particles
Although it was believed for a very long time that protons, neutrons, and electrons were the smallest particles, they were wrong…
Types of particles
1. Baryons (include protons and neutrons)
Made up of three smaller particles called quarks
2. Mesons
Made up of two quarks
3. Leptons (include electrons and neutrinos)
4. Bosons

10. Antimatter
Antimatter: Matter that has all the same properties as the regular matter except the electric charge is reversed Example: positron (anti-electron), has the same mass as an electron, but is positively charged Antimatter does not occur in the natural universe as far as we know. It can be created in labs in very small quantities.

11. Matter – Antimatter Interactions
When a particle and an antiparticle meet, both are turned into pure energy
Matter – antimatter reactions are the most energetic reactions in the known universe
Example: If 500 kg of water were added to 500 kg of anti-water, the energy released would be able to power the entire US for a year!!