Lecture 1 Flashcards
(28 cards)
Everything is made up of —–
Atoms
Electrical forces act on the protons and electrons because they have which property
Electric charge
Do neutrons experience electric force
no because they have no charge
What is contact/normal forces, friction, and drag forces fundamental origin?
electric force
What is the reason that when a solid object comes into contact with another they exert forces on each other
Because the e- in the atoms on their surfaces repel (very strongly when they come close)
What is the reason that when an object t slides against a surface there is a “friction force”
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
What is the reason that when an object moves through air or water there is a “drag force”
Because because the object approaches air or water molecules which repel it due
to electric force
What is responsible for hold an atom together?
Attractive electric forces between the electrons and protons
Why do electrons not collapse into the nucleus due to electric forces
Because they have kinetic energy
Why do protons inside the nucleus exert large repulsive electric forces on each other, but they do not fly apart
a different type of force called the
“strong nuclear force” holds them (and
the neutrons) together
What is the reason that some protein molecules bind to DNA
Electric force
Does decreasing the distance between two objects increase or decrease the magnitude of the force
increase
If an object has Np protons and Ne electrons, it has net charge:
Q = Q(all protons) + Q(all electrons) = eNp + (-e)Ne =
e (Np – Ne) *e= 1.6E-19
Q>0 means total (net) charge
positive
Q<0 means total (net) charge
negative
Q=0 means object is
“uncharged” or “neutral”
T or F : ANY object made of any atoms can have a net charge that is positive, negative, or neutral
True
Why is the charge of a typical object usually 0
its atoms usually have equal numbers of
protons and electrons
If the object interacts with other
objects it could ——-
gain or lose (transfer)
electrons or protons and become charged
Rubbing a balloon on hair
- 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
Why after a while charged objects may gradually go back to being neutral
because electrons can transfer to or from air molecules when they collide with the object
DNA charge in solution: In water, the phosphate
groups on DNA release protons into the solution.
The DNA ends up with a net negative charge (it has more
electrons that protons)
Conductor definition:
materials in which many charges can move relatively freely through the whole object
Conductor examples
Metals and salt water (dissolved Na+ and Cl- ions can move relatively freely)
