Planet Earth

Force Laws in Nature - Dynamics

kinds - sources - strengths - ranges - mediators

Review• Newton’s Laws

– Law of Inertia - definition of mass– F = ma– mutual interaction

• These give the existence and strength of all forces

• There seems to be a myriad of forces we deal with each day - they all can be related to just 4!

Force Laws

• Gravity

• Electricity and Magnetism

• Strong Nuclear

• Weak Nuclear

Gravity Force

• Distance behavior• source of the force

– cause?

• receiver - what can feel the force

• 1/r2

• gravitational charge - mass (m)

• gravitational charge - mass (m)

F = Gm1m2/r2

ATTRACTIVE ONLY - LARGE SCALE STRUCTURE/STABILITY OF THE UNIVERSE

Electric force

• Distance• source• receiver

• 1/r2

• charge(q)• charge (q)

F= kq1q2/r2

ATTRACTIVE AND REPULSIVE - STABILITY OF THE ATOM/MOLECULES/MATTER

Strong Force

• Distance• source• receiver

• Scotch tape 10-13cm• many “charges”• many “charges”

??????????????

ATTRACTIVE AND REPLUSLIVESTABILITY OF ATOMIC NUCLEOUS

Weak Force

• Distance• source• receiver

• Scotch tape 10-16cm• many “charges”• many “charges”

????????????????

Radio active decay - instability of matter

Range

• Gravity• E & M• Strong• Weak

• Infinite• Infinite• Short 10-13 cm• Very short 10-16 cm

Strength

• Strong• E & M• Weak• Gravity

• 1• 10-2

• 10-13

• 10-42

Mediators

• Strong• E & M• Weak• Gravity

• Gluons• Photons• Weakons• Gravitons

Exchange particles (1949) vs. Action at a distance /field concept (19th century)