Abeka Physics Section 8.3

Question 1

Any force acting on a body obeys what?

Answer 1

any force acting on a body obeys the laws of motion.
>it produces acceleration in agreement with rule a=F/m (Newton’s 2nd law of motion)
>it experiences an equal and opposite force of reaction (Newton’s 3rd law of motion)

Question 2

List the four categories that physicists usually group forces into

Answer 2

>strong force
>electromagnetic force
>weak force
>gravitational force
>these four forces are considered to be the four fundamental forces of nature

Question 3

Describe the strong force

Answer 3

> strongest of 4 fundamental forces: strong force
more than 100x’s stronger than electromagnetic force
is cement that holds atomic nucleus (neurons and protons) together
in theory, it is reciprocal attractive force (protons and neutrons attract each other; not simply that one attracts the other)
operates over very short range hardly extending beyond distance equal to nuclear diameter

Question 4

Describe electromagnetic force

Answer 4

> exists only between electrically charged bodies
is reciprocal force (may be either of attraction between bodies of unlike charges or of repulsion between bodies of like charges)
its reciprocal nature is basis of action-reaction
unlimited in range, but diminishes in proportion to square of distance between charged bodies (if distance is doubled, force is reduced to 1/4; if distance is tripled, force is reduced to 1/9)
binds electrons to nucleus within an atom
responsible for attractions existing between 2 molecules at small distance of separation: positive nucleus of one atom attracts negative electrons of another atom
responsible for resistance of one atom to penetration of its space by another atom: one atom’s electron cloud is a shield that repels electron cloud of other atoms (this resistance is what you feel whenever you touch something)
in general, every force due to contact between objects is electromagnetic in origin

Question 5

Describe weak force

Answer 5

> responsible for certain particle interactions in radioactive decay of atomic nuclei (for instance, 1 of products of beta decay is particle called anitneutrino, which is almost massless but exhibits weak force)
has extremely short range extending barely beyond its point of origin
scientist think that there is almost 0 attraction between antineutrino and ordinary matter (matter composed of protons, neutrons, and electrons)
scientists theorize that antineutrino can penetrate millions of kilometers into earth because of its near-zero attraction to surrounding matter
been proposed recently that weak force and electromagnetic force are basically different expressions of same force

Question 6

Describe gravitational force

Answer 6

> weakest of all 4 fundamental forces
exists between any 2 bodies of matter
is reciprocal attractive for only, not producing any repulsion effects
diminishes in proportion to square of intervening distance
is what holds moons, planets, and stars in their orbits
gravity generated by massive earth on which we dwell is felt as powerful force of weight