phys (0219) - Space: E = mc^2

related to mass dilation again..

this goes against what chemists say about matter not being able to be created nor destroyed, but einstein suggests that matter can be turned into energy, and energy into matter, at the speed of light of course.

because as speed increases, mass increases (mass dilation) so the faster you are, the heavier you are. so imagine being at lightspeed, mass would be ginormous man. i dunno what i can say about this formula, i'm not einstein hahaha.

basically.

E = energy
m = mass
c = speed of light

and the ^2 is significant coz it makes the numbers really big. and that's actually true hahaha.

phys (0217) - Space: alpha centauri

discussions today about what costs there would be to get to alpha centauri.

thing is, for the astronaut, the trip would seem shorter (timewise and spacewise) for them due to time dilation and length contraction. their mass would dilate too, but because of that, crashing into something would be catastrophic. they wouldn't be able to change direction either, not at that speed.

if they made it there and back, they would be younger than the people who were the same age as them when they left. costs would be enormous, especially for fuel, and our technology isn't that advanced. also, the idea is impratical because we wouldn't be able to communicate with them if they were travelling at the speed of light. not to mention it would still take years to travel there and back at that speed (around 8 both ways)

phys (0215) - Space: mass dilation

this lesson was actually about simultaneity as well.

an example for simultaneity would be lightning simultaneously striking two sides of the same carriage on a train. an observer would see both bolts of lightning hit either side of the train at the same time.

however a person on the train itself, would see the bolt of lightning on the front of the carriage first, since the light has less area to travel, it arrives sooner.

mass dilation is a strange theory, that only applies when approaching near-light speeds. energy can be converted into mass, and vice versa, so at those kind of speeds, mass would increase making the object heavier, thus slowing it down.

sort of like momentum.. sort of, but for extremely high speeds.

phys (0209) - Space: time dilation

i learned this later than other people because i haven't been in class, but since zhou had a free he raided our class. he should do that more often, i mean i work better (especially in physics) when he's around.

cool here's a snazzy feature i never used, image URLs


see its all relative. the two ts represent whatever frame of reference you're looking at. the two different objects.

c is equal to the speed of light, 7 x 10^8m/s

phys (0129) - Space: gravitation

first lesson in new physics class. apparently they're ahead of ours, but i'm not quite sure if that's accurate. if they are, it doesn't seem like much of a gap, nonetheless i'm gonna have to look it up.

so we combined and discussed two formulas today..

F = (mv^2)/r [centripetal force]

and

F = G (m1m2)/d^2 [gravity between two masses]

to understand motion of satellites.

just to keep in mind, G = 6.67x10^-11, radius of earth is approx 6400km again in case i forget, and earth's mass is equal to 6x10^24kg

phys (1207) - Space: analyzing centripetal force

mr robson kept stressing how important it is to analyse things properly.

he went through a process of analyzing uniform circular motion.

first we describe their motion. (uniform and circular, duh)

they have a constant veloctity, but since their direction is changing, there must be an acceleration

F = ma, since there's acceleration, then its assumed there is a force.

that force we then describe.

in a hammer throw, its caused by tension, the pull of the thrower. in a car race, the reaction force is slightly tilted, but gravity is still straight down. add up the vectors and you have a force pulling in a direciton buddy. and with the moon orbiting the earth, its gravity that is pulling on the moon, the force that causes the acceleration

phys (1201) - Space: rocket acceleration

practice question today, worth 4 marks, and after doing it, we had to mark other peoples responses to it.

the question asked to describe the acceleration of a 3-stage rocket anda bout the g-forces felt by the astronauts.

in the graph shown, g-forces gradually increased, dropped whenever an engine was shut off, and hit 0 between stages. that 0 would be when there's no thrust at all, in between stages, when a bit has been dropped off. free fall. because there's no reaction force acting on the rocket opposing gravity, so there's not even 1G.

now the acceleration increased because thrust (F) was constant, and mass (m) decreased as fuel was burned. to keep F=ma true, acceleration increased as mass decreased, and the formula for g-force is g-force = (g+a)/g so as a increased, the g-force did too.

we also did one more question, about conservation of momentum.

in a closed system like this, the rocket on the launch pad would have 0 momentum. but as it lifts off, it gains a momentum, and the fuel kicked out the bottom has momentum too, opposite and negative, so they add up to the initial momentum, 0, proving conservation

phys (1130) - Space: conservation of momentum

man i shouldve been paying more attention instead of doing maths, but i had tests to prepare for.. but i managed to get SMOEthing into my head.

we all know newton's second law, F = ma, now rockets move because there's a net force. that is, a netforce acting upwards, that's higher than gravity (something different to reaction force coz thats only enough to counter gravity, not push the rocket further)

the rocket burns fuel, it pushes it out, and as a result the fuel pushes the rocket upwards (newton's third law)

robson derrived the formula for momentum (p) from F = ma today, it goes like this

F = ma [where a = (v-u)/t]
F = m((v-u)/t)
F = (mv-mu)/t
Ft = mv - mu = /\p

see?

phys (1127) - satellites to planets 2

today.. we went over.. just one concept i think.. one concept with multiple aspects.

it's that the movement of the earth affects the movement of the satellites that we launch.

mr robson described the axis spinning sort of like jumping off a moving train. when we jump, we still have the velocity from when we were on the train (aka, we're moving sideways though we dont realize)

that is why, launches are preferably done near the equator (rotational veloctiy is at its max there) and using the earth's rotational velocity to give the rocket extra speed is a good idea. 11km/s is the requried escape velocity to get out of the earth's gravity.

the earth is going anticlockwise (from looking above the north pole) around the sun, at a speed of approx 29km/s, so in theory.. satellites we launch are also following that same path, with that same speed. so to fire rockets in the opposite direction, unless they exceed 29km/s, the result wuold just be the rocket slows down and is pulled towards the sun. if its fired in the same direction, it escapes earth's orbit and goes elsewhere.

also.. i asked if all the planets were on the same plane.. turns out they are.. with the exception of pluto. i suppose they're in line with the sun's.. "equator"

also, before the lesson, as a question of gerenal interest i asked what fire is. no full explanation as yuet, it's not something that can be easily explained. but what we see and feel of the fire is energy for sure, but fire itself is more like.. a reaction.

phys (1126) - satellites to planets

we were split into random groups today based on randomly given out cards. in each group, we had to work on a particular question, of how to get a satellite to a particular planet.

for us, that was mercury.

we had to decide how to aim the rocket at mercury, whether or not to slingshot it around venus, and how the earth's orbit, other planets' orbit, and the sun's gravity affected the movement of the satellite.

from the north pole (looking down on it), we divised that the earth's axis and all the orbits were going anti-clockwise.

we havent yet reached a conclusion.. but i decided i'd want to be accurate with the answer, and proposed to my teammates tommy & bob that we should measure the orbit.

i got approx 0.3cm = 1 day (assuming earth's orbit is 365 days)

using this, and the estimated speed of the rockets (udit said 30-40km/s, so i said 35) we should be able to calculate the time it would take for the satellite to get to mercury, and using that info, see where the planets will be (assuming the planets are in line when we launched them)

hopefully my idea works.

meanwhile, tommy did a lot of the devising in terms of trajectory & parabola and whatnot

phys (1124) - G forces

first day with robson as a tacher today. he's alright. he explained the g force things well at least, and a few other things.

g force is a ratio of normal weight against reaction weight. the reaction being an acceleration.

to calculate vertical g-force, we go

(9.8 + a) / 9.8

the 9.8 coming from the earth's gravity.

now since gravity has no effect on us in a horizontal direciotn, when calculating horizontal g-force, its just a/9.8.

the thing about standing on the ground, is that we have a reaction force lifting us off the ground. that would be equal to gravity (9.8). so, our weight would be 1x normal, we experience 1g. apparently normal people can experience more than 3g (evident on rollercoasters and such). they target rockets and shuttles to only have around 3g for safety of astronauts and equipment.

if we fell off a plane though, there's no floor pushing us off, we fall to gravity, thats called freefall.

the thing about g-forces, is that they're independent of peoples mass. its the same ratio, but used on different people.

eg.

a 50kg guy, and a 100kg guy experience 2g.

the first guy experiences 100kg as his weight, and the other guy, 200kg.

the amount increases depding on how much the person weighs to begin with

i asked mr robson what would happen if two planets were really close to each other. he said that there would be a point in between where we would just be stationary in the middle, otherwise it'd be up to the stronger planet.

he explained what spaghettification is. he said that in a black hole, if we fell feet first, our feet would be closer to the black hole than our head, so our feet would be pulled faster, making it stretch. catch it?

phys (1119) - Space: space scientists

just a few vague outlines on some space scientists.

there was galileo of course, he used his own made telescope to observe things.

newton actually thought of the idea that chucking an object at the right speed will make it orbit the planet, and chucking it more could let it escape gravity. it turns out that the speed required for this is 11000km/s. newton also suggested that the same principles of gravity on earth, were the principles of celestial gravity as well (which was weird coz people thought they were two different things)

von braun was a german scientist. after WWII, the scientists who made rockets to attack the UK were split and sent to either USA or USSR. von braun was sent to USA. he worked on space program there. von braun designed the original rockets.

oh there was this dude who propose a 3stage rocket, but i forget who. but usually.. rockets were lauched in 3 stages, and that included the recent shuttles, except the shuttles dropped the liquid fuel part so high up that it burnt up on the way back in.

rockets are mostly fuel. fuel to keep going.

oh we talked about satellites.. and how usualy satellites are designed to come, and yet there are some that we sent off out past our solar system (voyager I and voyager II) we still get faint signals from them.. the mars rovers are still going around even though they were meant to die yearsa go.

oh and mr pitt said something weird.. i forget what it is. something like.. to slow a satellite down, you have to speed it up twice. i forget how it works.

phys (1117) Space: [c] analyzing flm

we were in computer room 11 today, after mr pitt arrived late. i couldnt tell my epic tale of how i put a fire out in the boys toilets -.- some juniors lit heaps of paper towel on fire.

anyway.

we used the program logger pro, to put dots on each frame of our video, and graph the resuts.

as expcted, the y displacement vs time was parabolic, and x displacement vs time was a straight line.

woohoo for accurate predictions! must get that file now.

phys (1116) Space: [p] filming trajectory

today we did a prac, a familiar prac, about throwing a basketball and filming it. we'll analyze it and further work with it later.. but for now.. we discussed things about it first, then filmed it.

we decided to use the big pipe thing coz it measured up to be 2m long, and it would be totally visible in the video.

the thing was the scale had to be in the same plane as the trajectory (in order to produce accurate results/readings)

oh and apparently the scale might not have been exactly 2m accorind to zhou and monger

wth monger is an english word? haha

and i suggested the camera has to be at the right angle, it cant be looking up or side on of the ball, the lense has to be parallel to the plane of the trajectory (in terms of x and y movement)

catch me?

so we went out, and i filmed udit and tommy throwing the ball back and forth.. hopefully we got some good shots

phys (1112) - Space: projectile motion

so talking about projectile motion today, after watching a few random videos of projectile motion in action in real life.. ie people jumping, flying around etc. a lot of ski bail videos too haha.

when talking about projectile motion, horizontal velocity is constant, but vertical is not. this can be shown with a diagram that follows an object being for example thrown, and ruled from the centre.

usually we get a parabola-like shape for these kinds of diagrams, and they are symmetrical about a vertical line somewhere in the middle, this is assuming air resistance doesn't really affect the throw (like it would with say a ping pong ball) also the time it takes on either side of that vertical should be equal.

i cant remember much else we talked about.. but mr pitt said he would send us an email witht he powerpoint that we used today.

phys (1106) - skiing parabola

not much to note here, we were calculating the x and y displacement of a guy skiiing.

the most efficient way to do this is to make lines from the centre of gravity off to the side somewhere, to measure to scale.

me and amanda did the wrong thing -.- but oh wellers.. it's right now.

plotting our results will just give us a parabola, so plotting y against x^2 should give us a straight line if we were correct

phys (1105) - Space: motion detecting pendulum

we walked in, puzzled from our homework about the motion sensor prac thingo, to find that mr pitt had it all set up alerady.

the pendulum was hanging off a force detector, and in front of a motion detector.

so we timed the period using the motion detector, then calculated it using the formula to see if it was consistent.

then using the force results, there were 10 high force readings within 7.5 seconds. what happened was.. the kinetic energy is highest at the equilibrium point, coz thats when its at its fastest before it slows down while going upwards. and it hits that point twice peroscillation. so we end up with 1.5 as the period, consistent again.

then timing it again.. we all started getting 1.3, and the force said 12N suggesting that gravity in creased.. it took the class i while to realize mr pitt shoved a supermagnet under the desk to rig that last set of results -.-

phys (1102) - Space: pendulum period formula

before we got stuck into more formula stuff, we first did a few HSC 2008 questions, which i did correct.

we talked about energy conversion in a rocket taking off.

chemical energy decreases, coz it is burnt up and converted to kinetic energy (which increases) and gravitational potential energy (which also increases)

even though its a negative value, it increases coz it gets closer to 0

as for kinetic energy, the movement of the rocket is because a net force acts on it, caused by the thrust of the engine.

if the rocket kept the same thrust, the rocket would keep accelerating, coz mass decreases, so for force to stay the same, acceleration increases (F = ma) full metal alchemist broz

so to slow down the rocket, the thrust is reduced (its important to keep an eye on acceleration coz some rocket equipment can die to pressure, so can people)

then we talekd about pendulums, the formula for period iiiiiisss..

T = 2(pi) root:(l/g)

yes thats crappy -.- but i have no symbols here haha.

and the gravitational force between any two masses isss..

F = G(m1m2)/r^2

yeah..

then we talked about weighto n other planets, which we did not finish this lesson

phys (1030) - Space: [p] pendulum length

the class split into groups to do one length of string for the pendulum each.

our group did 0.8m.

each group measured the period for 4 trials then took an average.

all groups used the same mass ball on the end of the string to not rig up the results.

the experiment was to test whether length had an effect on the period of a pendulum swinging.

my prediction was longer ones would take longer, and thats what the class' results show.

phys (1027) - Space: gravitational potential energy

earlier today we talked about gravitational potential energy.

we discussed that in previous years, potential energy was given with the formula

E = mgh

where m is the mass, g is gravity (aka 9.8) and h is the height of the object.

today we went over a different equation.. one thats more constant.. because the first one, assumes gravity is constant, whcih it isnt.. the higher above the earth you are, the weaker gravity gets.

E = -(Gm1m2)/r

they are meant to be subscript 1 and 2 btw.. the m represents the mass of the two objects in which gravity is acting, and G is the constant gravity thing we were talkinga bout