Obeying the law (of physics)! Kinetic energy and momentum explained----make money online

hello in my video on crooks radiometers

i dispelled the myth that these are

actually spun around by photon pressure

and i said that if in fact photons

caused these to spin they would go the

other way because photons bouncing off

the white sides would impart momentum

and cause them to spin the other way

than they actually do but wait one of my

viewers actually said if the photons

bounce off the white veins they have a

certain amount of kinetic energy when

they come in and if they have the same

amount of kinetic energy when they come

out how could they be giving any energy

to the rotor so in today's video i'm

going to talk about kinetic energy and

momentum and if you haven't heard of a

Pelton wheel stay tuned because it's

actually a pretty cool thing

as with many physics demos we start with

an object from a science museum gift

shop this is called Newton's Cradle and

it works by lifting one of the balls on

one side giving it some potential energy

and when we let it go all that potential

energy is converted into kinetic energy

and it hits and a ball will come off the

other side so I'll show you that now

pretty good and if everything were

perfect the the middle balls here

wouldn't be moving at all and so just

one in and one out so let's take a look

you might remember that kinetic energy

is one-half times the mass times the

velocity squared and velocity is a

vector quantity there is direction

associated with velocity but since its

squared this whole quantity is scalar so

the kinetic energy of a golf ball you

know is the same as the kinetic energy

of a space shuttle or whatever it

doesn't matter what direction or what

mass this is just one scalar quantity so

according to the formula if we lifted

two balls on one side like this we would

have twice the mass and when we let them

go they'll come down it will have about

the same velocity as we as just lifting

one ball and therefore will have about

twice as much kinetic energy so

therefore we could do the math and

figure out how fast this last ball is

going to come off if we have twice the

total kinetic energy we can figure out

how much quicker that last ball is going

to come off so what we should see is two

balls lifted up hitting and then this

list the last

coming off more quickly than it did the

first time so let's try it we'll pick up

- and it doesn't behave the way that I

described

we're expecting one ball to come off

this side going faster with two balls

going in on this side and you know what

do we miss here obviously the experiment

doesn't match so we must have missed

something but the equation is correct we

have more kinetic energy going in

therefore we should have more kinetic

energy coming out what's interesting is

that we need another formula to figure

out how to define this physical system

the problem is that kinetic energy alone

can't describe the full mechanics of

this situation because there is no

directionality to it since it has this

velocity squared term in here there's no

more vector information so what we have

to add is the momentum equation and this

one is just mass times velocity but it's

not squared and since velocity is a

vector meaning it has Direction

associated with it then the momentum is

also a vector quantity let's try the

same thing again this time lifting three

balls as you can see it always works

there's always the same number of balls

on the outgoing side as the incoming

side we can even try it before in this

demo I'm going to show you that momentum

is conserved even if kinetic energy is

not so remember that total energy can't

be created or destroyed but we certainly

can convert kinetic energy into

something else and that's what I'm going

to show you right now so I have two

rubber balls here and notice that they

behave very differently that one doesn't

balance very much at all and this one

balance is quite well so to investigate

this a little further I have a force

sensor a flat piece of plastic here that

acts as a force sensor on this aluminum

bar and it's connected up to a sensing

circuit and that is connected up to the

oscilloscope and I'll do another video

talking about oscilloscope setups but

here we're just going to talk about the

physics

and when I tap on the force sensor you

can see that the oscilloscope registers

the force applied over time and I've

also set up the oscilloscope to provide

the time integral so the red line is

actually the integral of force over time

so if I just tap it very lightly you can

see that the integral becomes a steady

state value and that corresponds to sort

of the total amount of force over time

so let's drop each ball on the force

sensor and see if there's any

differences in the graphs they produce

I've set up my desk line up here so that

I drop them from the same height and

it's centered right over the force

sensor so we'll start with the non

bouncy ball okay and you can see that

the value the red line has leveled off

now let's try the bouncy ball as you can

see the red line is quite a bit higher

indicating that there was more force

applied over time to the bouncy ball now

hold on a sec you might be saying maybe

the two balls don't have the same mass

and actually you'd be correct but as it

turns out it's the non bouncy ball

that's about 20% heavier so the heavier

ball actually had a less a lower force

applied to it in this test because of

the momentum transfer so with the bouncy

ball we had this momentum coming in and

after the balance after the contact it

came shooting back off this metal plate

therefore there was more momentum

imparted to the ball by the the table

the metal block and the earth and that

caused that required more force to be

pushed into the ball whereas the non

bouncy ball came down and stopped and

there was a very small rebound which

means that less force was put into the

ball to push it back up into the air now

the masses are pretty close and so

dropping him from this height means that

both of these have about the same

kinetic energy when they hit and yet one

of them had more momentum coming out so

where'd the kinetic energy go well the

non valancy ball converted it to heat

the bouncy ball retained most of the

energy

you know it came in with about the same

kinetic energy as it left with but the

non bouncy ball see here the non bouncy

ball converts it mostly to heat and so

if we did this experiment a hundred

times or maybe even a thousand times we

notice that the non bouncy ball is a

slightly warmer after doing this because

it's converting more of that kinetic

energy to heat and another clue you

notice that the sound of impact is

different the non bouncy ball has a much

sharper louder impact sound and that

gives you another clue that more energy

is being converted from kinetic energy

into something else and in this case

sound waves another thing to notice is

that in the bouncy ball case the

incoming speed was about the same as the

outgoing speed after the collision and

this is a consequence of how the

momentum rules work so if you've ever

seen a rubber ball bouncing out into the

street and then hit by a moving car

you'll know that the ball actually comes

off from the car faster than the car was

going in fact it will be about twice the

cars speed because the car is much more

massive than the rubber ball and so all

that momentum transfer will go into the

rubber ball and it will actually be

going twice the speed it's just how the

equation comes out however remember that

motion is relative so if you're standing

on the street it looks like the ball is

going twice as fast as the car however

if you're in the car it looks like the

ball was approaching you at a speed that

is half and then after the collision

it's receding away at a speed that was

half as what you deserve-- observe on

the ground okay so now we know that a

bouncing object will impart more force

to the thing that it hit and that's

because momentum is conserved and so if

this object is coming in and hits the

table and then bounces off that means

that the table did more pushing in order

to get this moving in the opposite

direction so remember it's a vector

quantity so if this is considered the

negative direction and now suddenly it's

going positive that means there had to

have been an equal amount of force from

this other object the earth the table

everything in this room to push it back

the other way

knowing this an inventor came up with a

clever way to make water wheels more

efficient so a conventional water wheel

just think of an old wooden you know

sort of standard old

water wheel has flat blades like this

and just the current of the water going

across the river pushes on the blade and

makes the water wheel turn or similarly

the water might run down the side of the

wheel and the gravity will pull the

water down the wheel and make it turn a

Pelton wheel has veins that are shaped

like a cup and there's a jet so that the

water is channeled into like a firehose

jet and the jet sprays the water into

the curved vane and the curved plane

turns the direction of the water around

so there's a great way to visualize this

head over to the kitchen and get

yourself a spoon that has a rounded

bottom like a measuring spoon and put it

under your sink faucet and turn the

faucet on and you'll see you can

actually feel that when you put the

spoon right side up the water changing

direction will cause the spoon to be

pushed much more firmly than if you turn

the spoon upside down and the water just

runs over the back side of the spoon as

you can feel with your own hand

changing the water's direction requires

more force now here's where it gets

interesting let's zoom in on just this

part of the Pelton wheel and I'll

explain where some of the confusion came

from so this is the the cup shaped part

of the Pelton wheel and this is the jet

of water and we're going to be shooting

the water in at speed V at velocity V

and that speed is measured relative to

the nozzles so this is not moving but

the Pelton wheel is moving and if you go

to the Wikipedia page it says that the

optimum speed for this whole system is

such that the the Pelton wheel bucket is

moving with an instantaneous linear

velocity of V over 2 so half the water

speed and we'll talk about that in just

a minute but what this means is that if

the Pelton wheel is moving away from

here at V over 2 and the water is coming

in at V that means that you know the

bucket is sort of running away from the

water stream as its shooting in and so

even if this thing is turning around if

it comes off at the speed that it went

into the bucket

remember the bucket is running away from

it so ideally the water is not moving

relative to the to the nozzle but it is

moving relative to the bucket so it's

coming

from the buckets point of view the water

is coming in at V over two and it's

leaving at negative V over two so we

have the same situation with the

bouncing ball it came in at the same

speed that it left if everything is

perfect however from the water jets

perspective the water is going in at V

and it's coming out at zero the reason

that I bring this up is that if you

approach this from a kinetic energy

standpoint you could say well this is

this is the ideal case because we have

energy coming in one-half MV squared and

the water is stopped when it's gone

through our apparatus therefore we've

extracted all of the kinetic energy from

the water this is true this is all

absolutely true and so this is the most

ideal case we extract the most energy

from them from the moving water it's

also true that looking at it from a

momentum case the water is leaving at

the same speed that it came in relative

to the bucket it's just that the bucket

happens to be moving and so it makes

this situation a little bit more

complicated let's talk for a moment why

the optimum speed is V over 2 if the

bucket were locked let's say we put a

pin in the rotor so that the whole

Pelton wheel couldn't spin we still have

the the water coming in at V and in this

case it would be leaving it negative V

since the bucket is locked here and we

have this system - such that the water

always leaves at the same speed it's

coming in and we'd be delivering a lot

more force since you know we still have

this momentum transfer thing going on

that would be pushing very hard on the

bucket but how much work would it be

doing zero actually because if the rotor

is not moving it can't do anything it

can't grind our flour or produce

electricity or whatever okay so that's

not going to work we're getting zero

work out of that even though we're

getting the maximum force

conversely let's say the bucket was

moving at speed V so it's running away

from the water stream at the speed the

water is going how much force would it

be producing in that case it would be

zero because you know the water doesn't

have a chance to push against the bucket

because the bucket is already running

away at the speed of the water jet so

the water doesn't really have any

ability to push on it any in both of

these extreme cases we're not getting

any work done out of the water because

either we have no

speed in one case and we have no torque

in the other case and as it happens the

ideal speed is halfway it's V over two

and I don't think I'm going to go into

the math derivations for that but but

this is the ideal speed to get the most

work out of the water okay and so now we

come to the radiometer itself remember

isn't it is not the photons that make

this spin but there is such a thing as

light pressure so in a perfect vacuum

with enough light you could make it spin

due to photon pressure and what's

happening is when the photons hit the

black side of the veins that kinetic

energy is converted into thermal energy

just like with the non bouncy ball and

when the light hits the reflective vein

the photons that are reflected off in

part more momentum or force on that vein

which would cause the rotor to spin with

the lighter veins trailing so now we

have to figure out how much momentum we

get from the photons well we know that

momentum is mass times velocity oops I

mean photons are massless therefore they

have no momentum well not so fast the

trick is that photons do have momentum

because they're going fast enough for

they have a relativistic mass and we can

calculate that with a relatively simple

thing but I'm not going to go into it

right now we should have the same issue

that we had with the Pelton wheel so if

the rotor is locked we're actually

holding it fixed and the photons are

bouncing off the white veins they're

imparting a force and we should be able

to measure that force but are they doing

any work no because the rotor is locked

we're not actually getting any work out

of the system when we allow the rotor to

spin we actually will be extracting a

small amount of energy from the photons

and I haven't done the math myself but I

suspect that the moving the moving vane

will actually redshift the photons very

very slightly and that's probably how

the energy is extracted this is a bit of

a guess on my part so I'd be curious to

hear what you think about this okay hope

you found that enjoyable see you next

time byegenuine online money earning sites, online work to earn money, online surveys to earn money, earn money through internet, best online income, earn money online data entry, easy ways to make money online, best online earning websites, top websites to earn money, online typing jobs for students to earn money, earn skrill money online, earn skrill money, best way to earn money from home, make instant money online absolutely free, trusted online money making sites, online income site, best online earning, money online, earn money from home, earn dollars online, earn money online, earn money online 2019, earn money online by typing pages, earn money online daily, online work at home and earn money, online earning, earn money online free, online money earning sites, earn real money online, e commerce ideas to make money, easiest way to earn money online,