Lecture 1

Question 1

Everything is made up of —–

Answer 1

Atoms

Question 2

Electrical forces act on the protons and electrons because they have which property

Answer 2

Electric charge

Question 3

Do neutrons experience electric force

Answer 3

no because they have no charge

Question 4

What is contact/normal forces, friction, and drag forces fundamental origin?

Answer 4

electric force

Question 5

What is the reason that when a solid object comes into contact with another they exert forces on each other

Answer 5

Because the e- in the atoms on their surfaces repel (very strongly when they come close)

Question 6

What is the reason that when an object t slides against a surface there is a “friction force”

Answer 6

Because
the surfaces are not perfectly smooth. Small bumps on one approach
small bumps on the other and these bumps repel due to electric force

Question 7

What is the reason that when an object moves through air or water there is a “drag force”

Answer 7

Because because the object approaches air or water molecules which repel it due
to electric force

Question 8

What is responsible for hold an atom together?

Answer 8

Attractive electric forces between the electrons and protons

Question 9

Why do electrons not collapse into the nucleus due to electric forces

Answer 9

Because they have kinetic energy

Question 10

Why do protons inside the nucleus exert large repulsive electric forces on each other, but they do not fly apart

Answer 10

a different type of force called the
“strong nuclear force” holds them (and
the neutrons) together

Question 11

What is the reason that some protein molecules bind to DNA

Answer 11

Electric force

Question 12

Does decreasing the distance between two objects increase or decrease the magnitude of the force

Answer 12

increase

Question 13

If an object has Np protons and Ne electrons, it has net charge:

Answer 13

Q = Q(all protons) + Q(all electrons) = eNp + (-e)Ne =
e (Np – Ne) *e= 1.6E-19

Question 14

Q>0 means total (net) charge

Answer 14

positive

Question 15

Q<0 means total (net) charge

Answer 15

negative

Question 16

Q=0 means object is

Answer 16

“uncharged” or “neutral”

Question 17

T or F : ANY object made of any atoms can have a net charge that is positive, negative, or neutral

Answer 17

True

Question 18

Why is the charge of a typical object usually 0

Answer 18

its atoms usually have equal numbers of
protons and electrons

Question 19

If the object interacts with other
objects it could ——-

Answer 19

gain or lose (transfer)
electrons or protons and become charged

Question 20

Rubbing a balloon on hair

Answer 20

• Electrons are transferred from hair to the balloon
• Hair ends up with a net positive charge
• Balloon ends up with a net negative charge
• Since electrons attract protons, the balloon attracts the hair

Question 21

Why after a while charged objects may gradually go back to being neutral

Answer 21

because electrons can transfer to or from air molecules when they collide with the object

Question 22

DNA charge in solution: In water, the phosphate
groups on DNA release protons into the solution.

Answer 22

The DNA ends up with a net negative charge (it has more
electrons that protons)

Question 23

Conductor definition:

Answer 23

materials in which many charges can move relatively freely through the whole object

Question 24

Conductor examples

Answer 24

Metals and salt water (dissolved Na+ and Cl- ions can move relatively freely)

Question 25

Insulator definition

Answer 25

materials in which charges can’t move freely through the object

Question 26

Insulator examples

Answer 26

plastics, glass, rubber, dry wood, and pure water, in which electrons usually remain tightly bound to the atom

Question 27

Electric force between two objects can be —- or —–

Answer 27

attractive or repulsive

Question 28

The magnitude of the force —— with increasing distance
between the objects

Answer 28

decreases