Physics Final Test - Part 2

energy

the measure of an objects ability to change its surroundings

unit for energy

joules (J) is the unit for energy

is energy is a vector or scalar

energy is a scalar with no direction

kinetic energy (KE)

energy of motion, mass and velocity affect KE

mechanical energy (ME)

kinectic energy and gravitational potential energy

KE is directly proportional to the square of the velocity, meaning…

KE is directly proprotional to the square of the velocity, meaning that if velocity changes by a factor of x, KE changes by a factor of x², so if velocity increases by 5, KE increasees by 25

potential energy

potential energy is the energy stored in an object as a result of its positional

KE equation

KE=1/2mv²

PE equation

PE=mgh

whatever height does, PEgrav does?

whatever height does, GPE does the same

the “zero level”

the zero height level is the arbitarily assigned 0 height from which the height of any object is measured

ME:

KE:

GPE:

ME: KE+PE, at any moment in time

KE: energy of motion

GPE: stored energy, potential to become KE

conservation of energy

gravity (internal force) is in the system

law of conservation of mechanical energy

in a closed, isolated system the total mechanical energy stays the same

becasuse of GPEm gravity is an internal force for energy

closed system

no objects enter or leave

isolated system

no object from outside the system puts a net force on an object in the system

examples of NOT isolated system

freefall, inclilnes, a lot of frice, applied force (gravity/free IS an internal force for energy)

external force

A force acting on an object in the system from another object that is outside of the system. If these forces are not balance out by another external force they will cause a change in the total momentum of the system.

internal force

A force acting on an object in the system from another object within the system. These forces can cause momentum transfers within the system, however they do not change the total momentum of the system.

momentum is directly proportional to

momentum is directly proportional to mass and velocity (p=mv)

to compare change in momentum use

to compare change in momentum, use: change in momentum=m(change in velocity)

closed system

no objects enter or leave

use equal but opposite changes in momentum to

use equal but opposite changes in momentum to explain conservation

how to set up a ptotal=p’total equation?

firgure out what type of collisions, draw before and after diagrams, find the momentum (p=mv) of each object before and after, plug in and solve

GPE

energy stored in an object as the result of its position within the earthes gravitatioal field, GPE=mgh

compare two locations using energy

KEi+GPEi=KEf+GPEf

work

how much energy transformation is caused by a force

cos(𝜃)

where θ is the angle between the force and displacement vector

unit for work

the unit for work is Nm=joule

is work a vector or scalar

work is a scalar

+work vs. - work

they are not showing direction, + transfers energy to an object, - transfers enegy from object

work is equal to

work is equal to change in energy

work done to raise something to a higher height

work done to raise something to a higher height = change in GPE

work done to change the speed of an object

work done to change the speed of an object = change in KE

unless specifically specified assume…

unless specifaically specided assume its one or the other: work to change hiehgt or speed

gravivy is the only _ force

gravity is the only conservative force

non-conservative work

work done by any other force would be non-conservative work (Wnc)

this is same as internal vs external

in an isolsted sytem there is no external force doing work to change the energy so …

in an isolated system there is no external force doing work to change the energy so the total ME stays the same

if there are external (non-conservative) force doing work the mechanical energy of the system will…

id there are external (non-conservative) forces doing work the mechanical energy of the system will change

mechanical advantage

simple machines are designed to give the user a mechanical advantage when doing work on an object

with a mechanical advantage, what happens to all the values?

same change in energy, same work. the advantage is less F, the trade off is larger distance.

overall, work done always the same, but you can trade force for distance

power

rate at which work is done

symbol for power

symbol for power is P

unit for power

unit for power is Watt (W)

scientifc notation - determine exponent pos or neg

positive exponent if large number

negatice exponent if tiny number

charge

is a property of certain subatomic particles, it causes those particles to exert forces on each other over a distance. (this is electric charge. gravitational charge would be mass)

in an atom, what sign is proton, electorn and neutron

proton: + charge

electron: - charge

neutron: no charge (electrically neutral)

how do charges interact (electic force)

opposite charges attract, like charges repel

what does it mean to be “charged” (net charge)

“charges” or “net charge” - an imballance of protons and electrons

what does it mean to be “uncharged” (no net charge)

“uncharged” ,“neutral”, or “no net charge” - equal number of protons and electrons

symbol for charge

symbol for charge is q

unit for charge

unit for chage is coulomb (C)

qelectron=

qelectron= -1.6×10^-19 C

qproton=

qproton= +1.6×10^-19 C

e=

e= +/- 1.6×10^-19

in q=ne, what is q

in q=ne, q is net charge

in q=ne, what is n

in q=ne, n is number of unbalanced charges

in q=ne, what is e

in q=ne, e is +/- 1.6×10^-19 C (the charge of one of the unbalaned charges)

in a gravity analogy, what is a charge

in a graviy analogy, charge is a measurable property that causes the electic force, just like how mass is a measurable property that causes gravitaional force

gravitiational force between two masses

Fg= Gm1m2/r²

in Fg= Gm1m2/r², what is m1 and m2

in Fg= Gm1m2/r², m1 and m2 are the masses putting force on each other

in Fg= Gm1m2/r², what is r

in Fg= Gm1m2/r², r is the distance between the centers of the masses

in Fg= Gm1m2/r², what is G

in Fg= Gm1m2/r², G is 6.67×10^-11 and is the gravitational constant used every time

inverse square law

inverse:

distance increase - Fg decreases

distance decrease - Fg increase

square:

disrance changes by factor of: gravitional force changes by factor of:

2 1/4

3 1/9

10 1/100

1/5 25

coulombs law

electrial force between 2 charges, F=kq1q2/r²

in F=kq1q2/r², what is Fe

in F=kq1q2/r², Fe is electic force (+repels, -attracts)

in F=kq1q2/r², what is q1 and q2

in F=kq1q2/r², q1 and q2 aew the charges putting force on each other

in F=kq1q2/r², what is r

in F=kq1q2/r², r is the distance between the center of the charges

in F=kq1q2/r², what is k

in F=kq1q2/r², k in 9×10^9 - electical constant

coulombs law, also INVERSE SQUARE

distance increases by x, Fe decreases by x²

distance decreases by x, Fe increase by x²

just because a charge is attracted or repelled, does not mean

just because a charge is attracted or reppelled, does not mean it will move

protons: dont typically move without the whole material object moving

elecrons: are often, but not always, able to move through an object, or from object to object

what type of materials can electrons easily pass through?

conductors: electrons easily move through (Ex: metal, water, people)

insulators: electorns cannot easily move through (Ex: wood, rubber, plastic, air, etc)

law of conservation of charge

you cant destroy or create charge, you can only transfer it (almost always electrons), to keep the total the same

methods of charging

friction, polarization, conduction, induction

charging by friction

when you rub 2 insulators together one may take electrons from the other. Both become charged, one +, one -

polarization

• when you bring a charged object near a neutral object it can cause the charges to move to separte sides of the neutral object.

• always attrated to the polarizing char

charging by conduction (aka contact)

if you bring a charged object into contact with a conductor electrons will transfer causing that object to share its charge with the conductor

grounding

connecting a charged object to the ground (or a large conductor) will make the object neutral

charging by induction

• is charging by polarization made permaneny by either physically separting the two sides or by grounding one side

• induces the opposite charge than the initial polarizing charge

what are the starting objects for charging by friction

for charging by friction you need 2 neutral insulators

what is the action for charging by friction

for charging by friction the action is rub the two together

what is the result for charging by friction

for charging by friction the result is both end up charged, one + charge, one - charge

what are notes for charging by friction

for charging by friction the notes are electrons tranfer from the object with lower electron affinity to the object with higher electron affinity

what are starting objects for charging by polarization

for charging by polarization the starting objects are 1 charged object and 1 neutral object

what are the actions for charging by polarization

for charging by polarization the action is bring the charged object close bu the nrutral one (if the neutral object is an isulator they can touch)

what is the result for charging by polarization

for charging by polarization the result is the neutral object retains the overall neutral charge, but the charge separates into a + and - side

what are notes for charging by polarization

for charging by polarization the notes are the attrative charge is always closer to the polarizing charge. this temporarty, one the polarizing charge is removed it goes back to neutral

what are the starting objects for charging by conduction

for charging by conduction the starting objects are 1 charged object and 1 neutral conductor

what are the actions for charging by conduction

for charging by conduction the action is touch the charged object to the conductor

what is the result for charging by conduction

for charging by conduction the result is the intital charge is shared. both end up charged the same as the original charged object

what is notes for for charging by conduction

for charging by conduction the notes is the original loses some of its charge so it is less charged, but not all the way back to neutral

what are the starting objects for charging by induction

for charging by induction the starting object is 1 charged object and 1 neutral conductor

what is the action for charging by induction

for charging by induction the action is polarize, ground the far side, remove the ground, then remove the polarizing charge

what is the result for charging by induction

for charging by induction the result is the neutral object ends up the opposite charge of the original polarizing charge

what are the notes for charging by induction

for charging by induction the notes are you can also make the polarization permanent by just physically separating the two sides, so they are insulated from each other.

what are the starting objects for grounding

for grounding the starting object is 1 charged object

what are the actions for grounding

for grounding the action is make a conductive connection to the ground (or to a much larger conductor_

what is the result for grounding

for grounding the result is the object ends up neutral

what are the notes for grounding

for grounding the notes are the ground takes electron from the charged object if it was negatively charged. the ground gives electrons if the object was positively charged