Stuff You Firfot Day Before ! Flashcards
Calculating acceleration and momentum
CONSTSNT speed = resuktsnt force 0, so reistsnce =driving force
However when the coupling breaks, the driving force stilk there, but no reistsnce less so there is a resuktsnt firce
Work this out divide by mass to get acceleration and also DRAW A DIAGRAM
Momentum has changed, means negative Monteur now?
Difference between base units and DERRIVED units?
Base units are those only THOSE THAT ARE BASE UNITS
DERRIVED QUANTITIES IS ANYTHING ELESE THAT IS NOT PAET OF THE 7
Prefixes need to know
FEMTO
Pico
Nano
Micro
Mili
Meter
Kilo
Mega
GIGA
Tera
PETA
FEMTO IS -15
Car stopping
Thinking and breaking
Thinking is reaction time and speed
Breaking is deceleration deoends on breaks road etc
Ways to determine g
Ticker tape connected to a ticker set at specific frequency
Drop mass
And count the dots and multiply by frequency to get time
Now can measure the distance they went for displacement and use suvat where s = 1/2at2
For graph sake can measure s against t2 for different masses I guess
Trapdoor
Where electroms get demagnetises drops ball which makes the clock start, and pass a trapdoor disconnect circuit snd time stop
But delay between hitting door, demagnetising
Better to nust use LIGHT GATES
Displamcent always
Is the minimum distance between two points straight linen
What is the centre of mass thought to be
A point where all mass is concentrated at
But also the point at which if a force is acted through, will only give rise to translational motion and no rotation !!!
How to plumb line
Suspend a body using a clamp
Allow it to come to rest, as here itsonly force, weight, will act through its centre of mass, and give rise to no rotational kvoement
Suspend a plumbline which will be the same thing l
And draw and rotate
Importsnt about things hanging, why do they come still?
BECAUSE THEIR WEIGHT ACTS THROUGH THEIR COM, GIVING RISE TO NO MOMENT WND THUS NO ROTATION
Drag
Is the force that opposes fluids
Determiend in speed and cross sectional area
Can be ignored if order is more than 1000 less
Can’t be when cross sectional area is much more bigger than volume
Or travelling at insane speeds as itsproprtionsl to velocity
Apparently drag to amss
Pressure equation
Is given by the total NORMAL FORCE / area
As we normally add up all the normal firces and then divide
Assumption to make when calcuaging density if mixtures ,
Find total mass / total volume
And assume that when mixed the moleucles do not react with each cpwhich can affect the densities
Pressure in fluids
Change in oressure
What is uothrust?
= dhg
And depends on height if the container that’s it assumign everything else constant
Change in pressure =change in height density x gravity
Ina. Column of liquid there will be different pressures acting at the top of the colourblind compared to the bottom
As a result , p = f/a , f = pa, there will be a difference of f which is = to change in pressure x area
(Newton’s third law causes upthrust , the weight of mass )
Equation is = to change in height x density x gravity x area
Now this is = to the weight if the FLUID DISPLACED as it is the volume x density of fluid
Thus the uothrust acting on an object is = to the eight of fluid displaced
Total pressure = atmospheric and water aswell don’t forgot
So for an object to float its uothrust must = its weight! If it csn’t do that resuktsnt force will always be down so it will just accelerate downwards
But if thrown in where resuktsnt force is something and in water uothust is always greater than object, then now resuktsnt force is up. Thus it will slow down until it monetarily 0 then accelerate up again. In this Tim this is changed by drag
Remember fraction of object under water is =
D1/d2
Where d1 is the density of object
As a result the densities are dependent of the ability to float
If density of object is less it will
If not it will fall
Definition for work done
1 joule energy needed to move a firce of 1n by 2 m in the direction
So remember work done is force x distance in direction firce is moved
And when we mean firce it can just be the WEIGHT TOO! If you only have that as the force then you are moving this up so be careful
On that note the force done = transferred to gravational store of that thing
So mgh is the same thing is w x d (force x d )
And if firce acted is not same plane then take the component in the same direction of the object thstsbeing moved!
Assumption fir gravational potential energy
Is that the grvstsionsl field strength is CONSTSNT at whatever height you go!
There we go, what happens if you lower object at same velocity, what happens to GPE
Velocity same, so GpE not Converter to kinetic energy, it instead thermal store of surrounding
But likely at normal times, it convert to kinetic as velocity changes, this happen in rollercoaster
Thus if you know height, you can work out final velocity, assuming that no resistive firces, because then here not all GPE is transferred into KE , but some into other stores
Power = fv!
Only can use when in constant velocity !
Because in constant velocity requires a CONSTSNT FIRCE ALONG A DISTANCE
THUS world done = force x distance (as this don’t change)
And in a certain time this jus becomes FV!
How to do PAGS
Ideally want a graph based on equation, so if f= kx, then plot F agains X and grsdient K for different values
Then describe experiment with safety featured
Say equipment with lowest uncertainty
Then repeats to make more accurate!!
Higher the UTS
The stringer it is
How to do PAG young modulus
Yiu can measure force against edge Sion again, thus the gradient is EA/L, which means work out area using average micrometer and length ruler you can work it out
So suspend a wire across length if table cmalling, use a control pulley for fraction set up geniere calliper which is 0.1 easure extension twke safety and you’re goofn
REMEMBER REPEATS !
Stress strain for brittle
Never plasticsllt deforms, elastic to properinsk then snaps
Why In a wire when deforms the grsdient is still the same?
Because of edtentsion the force is still the same before and after the bonds, like same constants just starting at a different started point
How to tell if Newton’s 3rd law not happening
This because they are happening on SAME OBJECT or DIFFERENT FORCE TYPES
Principle of conservation of momentum
For a closed system the total momentum in a specified direction is cinserved , unless external forces act upon them
How to investigate monetuj
Use air racks to reduce friction as much as possible, then light gates to measure velocities so you have massses and can sxplore monetuj
Elastic when KE conserved
Inelasric si when some Ke transferred to other stores such as heat or sound etc
Energy cinserved overall both times
Monetuj cinserved too
Why is total momentum always conserved
In a closed system when an object extends a force to snither object, it enters an equal force l so thst net force in thst direction is ZERO
Thus rate of change of monetuj must be = 0, thus change in momentum is 0 and momentum cinserved
Describe accerlwtion using imlukse graph
As f= ma, change in firces also mean acceleration, so if force going up so is acceleration etc
Impulse cinserved because time is constant, however impulse negative direction
Thus if impulse is negative , change of momentum is negative too?
P(XUA)
Is the UNION
This is basically EVERYTHING IN VENN DIAGRAM
Including middke
So same as
P of a + p if b
- middle cuz it would count twice
PNA is the INTERSECTION just the middke
Probability if bith events occurring? P Na
Is p a x p b
What is expected and what is complement
Expected is if oribailty 0,2 and trials 10, thrn 2
Don’t round
Compliment is the OPPSITE
It might be essier to use this if they all are the same, otherwise finding before is hard to go through all combinations
Either an even happens or not
So happening snd comokemtnisith 1- that probability b
Probability distribution ?
List all probailties getting Esch case of
And these should add to one
Discrete uniform distribution?
Where every falues pro silty can be found and listed
How to proves something is idmedpent
Find p a and p b
And p n b
If p a x pi = pnb, then they are independent
Because if a and b independent, probiotics of bith hapepnign si p a x p b
Simple random sampling
Every sample I’m the population has same chance of being chosen
Cluster sampling
Where population divided into subgroups and tou sample from there
Sample yr 11, can sample yr11s from different schools
Can only happen if this doesn’t change anything, such as the yr 11 doesn’t matter about what school he attends foesntinfluence
Poputinu sampling
Sampling somineon the streee
Advantage = quick and easy way to get data
Disadvantage via because sampling someone like at a street for shopping if they there they prolly will etv
Statrtificed samplijg
This is where you divide population into categories and start and popeotionsllt sample in Esch group a total amount you want
This is quite rpersentstove however might be hard to split into strata that’s proprtionsl enough for the population!,
Quota sampling
This is where you opportunity sample until you get required s,out
Advantage is cheap quick and easy to fill numbers
Dissavantge is gonna be biased
For example interview, people all gonna be there good and you filling numbere
Seele selefcted
Opts in
Biased
Systematic sampling
Like arrange in random order than pick s certain why before and sample this what
Good representative
Sometimes can’t order and need ti be ordered ifs idling t
Categorical data is any
Discrete vs ck tinius
Data that csn’t be used as a numerical value, so even like product codes using numbers are cstgrofisl
Discrete only take certain values
CONTINOUS is a range of vslued
Grouping data
Problem is thst raw data is lost (Like actual values)
So stem and leaf is grouped and raw data preserved
Can easily compare find median mode etc
Can interpret trends like median and quartile
Length of line gives shape of each distribution
Can also follow two different sets of data side by side whilst still grouped
Pie chart used for catgeriusl so is bar chart
But pie chart foed prooertionsl so lose data
But scales down to 360 easier tk see side by side
Vertical line großdeutschen don’t confuse the Reede to do with width being cinnected to data. Just a straight line
Again why pie chart vs histogram?
Pie chart for discrete and categorical
Histogram for CONTINOUS
Frequency diagram gives kbsurcceed insge thst greater area means more frequency , even tho not the case
(This is when unequal class width used)
As a result you need value thst is constant for area to be proprtionsl.
This is frewuency / class width = rewuency density
So calcite thid by and plot on y axis, then plot frewuency density against clsss width so that frequency is the area
But remember there may be a k factor too, need ti check what is consistent
Skewed data
If data is more positive then egwtively skewed, is more negative then positively skewed
If in middle symmetrical
Skewed means less dwindling
