1. II. Two of the 4 fundamental forces:
1. The _____________________ force, Fg, between 2 masses:
gravitational
Gm1m2 r2
Fg =
attractive
…is always ______________________
…is ___________________________ to the masses
…is ______________proportional to ____________ of r
…is _______________ , which can be seen because
the constant G = __________________________ is
__________ .
directly proportional
inversely
the square
very weak
6.67 x N·m2/kg2
tiny
electrical
2. The _______________________ force, Fe, between two charges
Fe =
???

2. separated by a distance…
Suppose two charges q1 and q2 repel each other with an
electrical force Fe=___. Then experiments are done… 10
Exp. #
using….
and….
separated by a distance…
new Fe 1 q1
2q2 2
3q1 q2 3
2q1
3q2 4 5 6 20 30 60
10/4
10/9
10/16
What can you conclude about the form of the electrical force?
It is directly proportional to the _____________ on each object,
and ___________ proportional to the ____________________
_______________________________
charge
inversely
square of the distance
between the two charges.

3. Coulomb’s Law: The electrostatic force, Fe, between
two charges q1 and q2 separated by a center-to-center
distance r is… q1 q2 r
Fe =
where k = ________________________________
= ________________________________
________________________________

4. Page 3: top

5. Coulomb’s Law: The electrostatic force, Fe, between
two charges q1 and q2 separated by a center-to-center
distance r is… q1 q2 r
kq1q2 r2
Fe =
where k = ________________________________
= ________________________________
________________________________

6. Page 1:
top

7. Coulomb’s Law: The electrostatic force, Fe, between
two charges q1 and q2 separated by a center-to-center
distance r is… q1 q2 r
kq1q2 r2
Fe =
the electrostatic constant
where k = ________________________________
= ________________________________
________________________________
8.99 x 109 N·m2/C2, with
q in coulombs and r in meters

8. Charles-Augustin de Coulomb
French
physicist

9. Ex: Cavendish "Weighing the Earth" Experiment:
When a ____ sphere
(m2) was brought
close to the barbells,
the _______________
attraction
caused the
thin wire
to _________ . Pb
thin wire
From the wire's
properties, the
______________
needed to make
the wire twist
that much could
be _____________
gravitational
force, Fg r m2 m1
Pb barbells
twist
estimated
Then Fg, r, m2 and m1 were substituted into:
G m1 m2 r2
Fg =
and this was solved to find ______ . G G
Once _____ was known, an object of
known mass m and weight w were used
to find ___________ unknown mass Me using
G m
Re2 Me
w =
Earth's

10. Coulomb’s torsion (twisting) balance:

11. Ex: Coulomb “charge" Experiment:
silk thread
When a charged
ball q2 was brought
close to the charge q1,
the _______________
attraction
caused the
thin wire
to _________ .
counterweight
electrical q1
From the thread’s
twisting, the
______________
needed to make
the wire twist
that much could
be determined.
twist r
force, Fe q2
k q1 q2 r2
Fe =
and this was solved to find k.

12. Note:
Fe is… …directly proportional to ____________
…and inversely proportional to ______
the q’s r2 Fe Fe Fe q r m
2. Fe is ___________________ if the charges are “opposite”
and_____________________ if the charges are “like”
attractive
repulsive
3. Fe is ___________stronger than the gravitational force
because ________ is ____________________ than ______.
MUCH k
MUCH greater G
4. Fe is an ________________________________force.
“at a distance”

13. Ex: Find the electrical force between two charges
q1 = +3.4 x 10-6 C and q2 = -1.7 x 10-4 C whose centers
are separated by a distance of 2.5 x 10-2 m.
kq1q2 r2
Fe =
(8.99 x 109 N·m2/C2)
(+3.4 x 10-6 C)
(-1.7 x 10-4 C)
Fe =
(2.5 x 10-2 m)2
(-5.2 N·m2)
Fe =
= N
(6.25 x 10-4 m2)
Is the force attractive or repulsive?
Which charge exerts a stronger force?
If released from rest, which would accelerate more?
attractive
neither
You can’t tell, since the masses are not given.

14. Ex: Two _______________ masses:
neutral Fg Fg
like
The same two masses with ___________ charges: Fg Fg Fe Fe
The same two masses but with _______________ charge:
opposite Fe Fg Fe Fg

15. Ex: Two electrons and a proton are located at the
vertices of an equilateral triangle as shown below.
The electrical force of the proton acting on one of the
electrons is shown. Draw all other electric forces.
Then draw and label the net (resultant) force acting
on each particle. R e- p R R e-

16. Ex: Because gravity and the electrostatic force are ____
____________ … so
similar
planet v
Gravity
___________
holds the
planets to
the Sun (S): Fg S
It was thought that the electrostatic force was responsible
for allowing the electron to ____________________________ .
orbit the nucleus v
electron
electrical
The ____________
force binds
electrons to
the nucleus (N): Fe N

17. In reality, orbiting electrons ______________________ Why?
are not possible!
1. Electrons in circular orbits ___________________.
are accelerating
2. Accelerating charges ______________________ .
radiate energy away
lose
3. Therefore, orbiting electrons would ________ energy
and _________________________________ and all matter
would ___________________in a fraction of a second
spiral into the nucleus
collapse
quantum mechanics
A better theory was needed, so _______________________
was developed. It says that:
1. The electron _______________________ , but
___________________________ orbit.
does not orbit
occupies a “stationary”
2. The “orbit” only tells you where the electron
is ____________________ to be found or the
_____________________ of finding it somewhere!
most likely
probability

18. The electron "cloud" is the modern idea of an electron.
Brighter areas are where the electron is more likely
to be found, i.e., has a higher probability of being
found. The electron does not "move around."
lowest energy "orbit"
higher energy "orbits"

19. Electron cloud model:
Electron
"cloud"
is _________
where the
electron
is _______
_________
to be found.
The ________
____________
are spread
out around
in the cloud.
electron
cloud
__________
densest
most
likely
charge
and mass
= __________
nucleus