physics1 (chap11)

quarks!

Mass-energy equivalence

Mass-energy equivalence

E = mc²

Two major categories of particles

• Bosons: photons, W/Z particles, gluons and gravitons

• Fermions

Quarks

Fundamental particles condensed from energy released in the early universe

Charge

( + / - )

Two positive particles will...

( + ) ( + ) Repel

Two negative particles will...

( - ) ( - ) Repel

Two particles of opposite charge will...

( + ) ( - ) Attract

Protons

• Composed of two "up" quarks, one "down" quark

• Positive ( + ) charge

• Mass = 1.672 * 10^-27 kg

Neutrons

• Composed of two "down" quarks, one "up" quark

• Neutral ( 0 ) charge

• Mass = 1.674 * 10^-27 kg

What are protons and neutrons collectively known as?

Nucleons, they are the particles that form the nuclei of atoms.

Electrons

• Leptons

• Negative ( - ) charge

• Mass = 9.109 * 10^-31 kg

Gravitational force

• Weak attractive force

• Infinite range

• Acts within a field established by collections of baryonic matter

Electromagnetic force

• A strong attractive or repulsive force (dependent on charge)

• Infinite range

• Acts within a field established by stationary or moving charged particles

• Moving charged particles produce electromagnetic waves.

◊ The particle equivalent of electromagnetic wave energy is quantized as photons.

Strong nuclear force

• Within the nucleus of an atom, electrostatic repulsive forces exerted between protons destabilizes the cohesion of larger nuclei.

• Strong nuclear force is a very strong attractive force exerted between nucleons over extremely short range.

• Exerted by bosons called gluons

• Electrostatic repulsive forces between protons and strong nuclear force between nucleons act in equilibrium within atomic nuclei.

Weak nuclear force

• The process of radioactive decay of unstable atomic nuclei is mediated by the week nuclear force.

• Extremely short range

• Exerted by weak bosons.

Contact forces

• Macroscopic object interactions are the result of microscopic electromagnetic force field interactions.

• The interaction electromagnetic force field range between macroscopic objects can be as small as an angstrom (10⁻¹⁰m), so objects appear to touch or come into “contact”.

Field forces

• Gravitational force, electromagnetic force, strong nuclear and weak nuclear forces all occur at range or within a “field”.

• Some models relate interacting field density to an exchange of virtual particles, but that will not be addressed in the scope of this course.

Forces resulting in a change in velocity

• Velocity changes can be the result of a change in the magnitude of a velocity.

• Velocity changes can be the result of a change in the direction of a velocity.

• A net force is required to alter magnitude and or direction of a particle.

Forces resulting in deformation

• Materials are composed of arrays of atoms linked together by electromagnetic forces.

• External electromagnetic forces may displace the relative position of individual atoms, while the material remains intact.

• This alteration of composite atom position is defined as deformation.

• Some materials have the capacity to return to initial configurations after an external force is discontinued, while others experience permanent deformation.

Inertial frame of reference

• A particle that is “stationary” within the context of its surroundings, or moving with a uniform velocity is defined to be in an inertial frame of reference.

• A particle within an inertial frame of reference is defined to have no net force exerted upon it.

• Consider a particle within closed container. If the container particle system is moving with a uniform velocity, from the point of view of the particle – the particle is stationary, with no reference points or net force evidence to indicate that it is within a moving system.

• Inertial reference frames are usually hypothetical constructs for simplification of problem solving and conceptual interpretation.

• The net force exerted on a particle in an inertial frame of reference is defined to be zero.

Non-inertial frame of reference

• Any particle that is experiencing a change in velocity (a≠0) is in a non-inertial frame of reference.

• A particle within a non-inertial frame of reference is defined to be experiencing a net force.

• All particles on the surface of the earth are in a non-inertial frame of reference because the Earth is revolving on its axis(1/day), translating on an elliptical path around the sun (1/365.25day), translating on an elliptical path around the Milky Way galaxy(1/250my), and accelerating through the universe.

Force relevance and frame of reference

• Gravitational forces are exerted at all scales and dominate at the largest distances and mass scales.

• Electromagnetic forces are exerted at all scales, and for our purposes are most relevant at contact force scales.

• Strong and weak nuclear forces are exerted at very small scales and are not considered in great depth in this course.