Discussion:
Automotive and kinetic energy, funding risk
(too old to reply)
Dave
2023-01-03 14:55:13 UTC
Permalink
Automotive brakes: these people obviously get cars to stop. So is the
heating proportional to velocity or velocity squared?

Say a 2000kg car at 120mph (moderately high performance, not
exceptional, about limit of normal cars)
or 30mph.

30mph - 13.4m/s
120mph - 53.6m/s

at 30mph - kinetic energy is 0.5*2000*13.4*13.4 = 179,560 J
at 120mph - kinetic energy is 0.5*2000*53.6*53.6 = 2,872,960J

Say 0.9G braking - 9m/s^2
0=54 +9*t^2
=> t= sqrt(54/9)
=> t= sqrt (6)
=> t = 2.44s, round up to 2.5

2,872,960 /4 = 718,240 , bit more at the front, say 750,000J

over 2.5 seconds, lots of watts. 3,600,000J = in 1 hour is 1kW

One second have 300,000J, which is a lot of watts and power for a
regular auto.

Stopping power = 300kw on one wheel, seems a lot to put brake pads say
200mmx100mm *2, even for a short time. Bearings, axle etc.

Electric car owners will have the luxury of knowing exactly how much
energy an acceleration cycle takes, and can compare and contrast.

The car people say that acceleration gets slower because of air
resistance as you get faster, not the extra kinetic energy needed,
because the square nature of the formula.

So, my expectancy is that if kinetic energy, and so gravity and a shed
more besides are wrong (E=0.5mv^2), physics across the planet will stop
being funded, since taxpayers don't fund kooks, and it is human nature
to throw the baby out with the bathwater. I'd give it 6 months.

Optics etc, I have no problem with, I was in about the first lab in the
world to have a room temperature thermal camera, and now I've bought one
online. On another personal note, I've worked for UK, American, French
companies, done an online course with Russians in Russia, and worked
more recently with people from the PRC. So all 5 should have a file.
They have permission to reuse my post on the three recent threads about
kinetic energy in whatever context (UN?), if they want a chin wag.

Saying kinetic energy is a computational convenience is OK to me, if the
exact same convenience is applied to free falling objects in a vacuum,
but where does all the energy from mgh lifting things up go to?
Jim Pennino
2023-01-03 15:10:03 UTC
Permalink
Post by Dave
Automotive brakes: these people obviously get cars to stop. So is the
heating proportional to velocity or velocity squared?
Who are "these people?

Brakes convert the kinetic energy of motion into heat.

The kinetic energy of motion is .5mv^2, therefor the heat is
proportional to the velocity squared.

<snip remaining clueless babble unread>
Dave
2023-01-03 16:28:27 UTC
Permalink
Post by Jim Pennino
Post by Dave
Automotive brakes: these people obviously get cars to stop. So is the
heating proportional to velocity or velocity squared?
Who are "these people?
Brakes convert the kinetic energy of motion into heat.
The kinetic energy of motion is .5mv^2, therefor the heat is
proportional to the velocity squared.
<snip remaining clueless babble unread>
Thanks. Model cars can be used, to show that 0.5mv^2 is needed. Spending
anything much is crazy (thought experiments are cheap). With full size
cars the v^2 from kinetic energy will be dwarfed by air resistance.
Jim Pennino
2023-01-03 16:52:16 UTC
Permalink
Post by Dave
Post by Jim Pennino
Post by Dave
Automotive brakes: these people obviously get cars to stop. So is the
heating proportional to velocity or velocity squared?
Who are "these people?
Brakes convert the kinetic energy of motion into heat.
The kinetic energy of motion is .5mv^2, therefor the heat is
proportional to the velocity squared.
<snip remaining clueless babble unread>
Thanks. Model cars can be used, to show that 0.5mv^2 is needed.
Needed for what?
Post by Dave
Spending
anything much is crazy (thought experiments are cheap).
Thought experiments without a full understanding of the math and science
are worth what you pay for them.
Post by Dave
With full size
cars the v^2 from kinetic energy will be dwarfed by air resistance.
If it were, the car would immediately come to a stop, which they
obviously don't.

To test that you can stand in front of a 70 kph wind and an 70 kph car.
Dave
2023-01-03 15:37:45 UTC
Permalink
Post by Dave
Electric car owners will have the luxury of knowing exactly how much
energy an acceleration cycle takes, and can compare and contrast.
To test this you can have an electric car very close behind a large
truck to reduce air resistance as much as possible. Really need a
private road for safety.
Jim Pennino
2023-01-03 16:22:02 UTC
Permalink
Post by Dave
Post by Dave
Electric car owners will have the luxury of knowing exactly how much
energy an acceleration cycle takes, and can compare and contrast.
To test this you can have an electric car very close behind a large
truck to reduce air resistance as much as possible. Really need a
private road for safety.
Electric cars don't have power or energy use meters, muppet.
Dave
2023-01-03 16:12:58 UTC
Permalink
Post by Dave
Automotive brakes: these people obviously get cars to stop. So is the
heating proportional to velocity or velocity squared?
Say a 2000kg car at 120mph (moderately high performance, not
exceptional, about limit of normal cars)
or 30mph.
30mph - 13.4m/s
120mph - 53.6m/s
at 30mph - kinetic energy is 0.5*2000*13.4*13.4 = 179,560 J
at 120mph - kinetic energy is 0.5*2000*53.6*53.6 = 2,872,960J
Say 0.9G braking - 9m/s^2
0=54 +9*t^2
=> t= sqrt(54/9)
=> t= sqrt (6)
=> t =  2.44s, round up to 2.5
2,872,960 /4 = 718,240 , bit more at the front, say 750,000J
over 2.5 seconds, lots of watts. 3,600,000J = in 1 hour is 1kW
Wrong there, sorry, there is no square root. Six seconds of hard braking.
Post by Dave
One second have 300,000J, which is a lot of watts and power for a
regular auto.
Stopping power = 300kw on one wheel, seems a lot to put brake pads say
200mmx100mm *2, even for a short time.  Bearings, axle etc.
answer is (300*6)/2.5 = 125kW, still a lot for normal cars on one wheel,
should survive.

A nice example of how easy it is to fool yourself to get the answer you
expect. This braking is absolutely fine from total energy into the axle.
Heating more of an issue? One time I checked my disks and there was a
dull red glow. They can take a lot.
Post by Dave
Electric car owners will have the luxury of knowing exactly how much
energy an acceleration cycle takes, and can compare and contrast.
The car people say that acceleration gets slower because of air
resistance as you get faster, not the extra kinetic energy needed,
because the square nature of the formula.
So, my expectancy is that if kinetic energy, and so gravity and a shed
more besides are wrong (E=0.5mv^2), physics across the planet will stop
being funded, since taxpayers don't fund kooks, and it is human nature
to throw the baby out with the bathwater. I'd give it 6 months.
Optics etc, I have no problem with, I was in about the first lab in the
world to have a room temperature thermal camera, and now I've bought one
online. On another personal note, I've worked for UK, American, French
companies, done an online course with Russians in Russia, and worked
more recently with people from the PRC. So all 5 should have a file.
They have permission to reuse my post on the three recent threads about
kinetic energy in whatever context (UN?), if they want a chin wag.
Saying kinetic energy is a computational convenience is OK to me, if the
exact same convenience is applied to free falling objects in a vacuum,
but where does all the energy from mgh lifting things up go to?
Dave
2023-01-03 18:00:39 UTC
Permalink
Post by Dave
Automotive brakes: these people obviously get cars to stop. So is the
heating proportional to velocity or velocity squared?
Say a 2000kg car at 120mph (moderately high performance, not
exceptional, about limit of normal cars)
or 30mph.
30mph - 13.4m/s
120mph - 53.6m/s
at 30mph - kinetic energy is 0.5*2000*13.4*13.4 = 179,560 J
at 120mph - kinetic energy is 0.5*2000*53.6*53.6 = 2,872,960J
Don't think I'll ever get to find out anything from brakes.

However an airtrack (e.g. 12m) might be OK. How can kinetic energy be
measured?

By doing work. e.g. lifting weights. Any temperature measurement has
too many inaccuracies. Need a kit with a hook to get caught by the car
with the wire connected via a pulley to a weight stack, and hopefully a
camera to film the high point, before it all comes crashing down.
Anything electrical needs full confidence in a whole lot more other
physics.

Giving different weights different accelerations and velocities should
be the easy part. Never got to use an airtrack at school or college.
The difference between kinetic energy and momentum is where you've lost
most people with physics.

Apologies for using usenet as a logbook, but there you go, don't like
secrets, and the other posters stop anything going too far off tangent.
Jim Pennino
2023-01-03 18:20:45 UTC
Permalink
Post by Dave
Post by Dave
Automotive brakes: these people obviously get cars to stop. So is the
heating proportional to velocity or velocity squared?
Say a 2000kg car at 120mph (moderately high performance, not
exceptional, about limit of normal cars)
or 30mph.
30mph - 13.4m/s
120mph - 53.6m/s
at 30mph - kinetic energy is 0.5*2000*13.4*13.4 = 179,560 J
at 120mph - kinetic energy is 0.5*2000*53.6*53.6 = 2,872,960J
Don't think I'll ever get to find out anything from brakes.
That's the first smart thing you've said in a long time.
Post by Dave
However an airtrack (e.g. 12m) might be OK. How can kinetic energy be
measured?
You might start by doing some research on how the rest of the world does
it.
Post by Dave
By doing work. e.g. lifting weights. Any temperature measurement has
too many inaccuracies. Need a kit with a hook to get caught by the car
with the wire connected via a pulley to a weight stack, and hopefully a
camera to film the high point, before it all comes crashing down.
Anything electrical needs full confidence in a whole lot more other
physics.
Nope, no research and off to la-la land you go.
Post by Dave
Giving different weights different accelerations and velocities should
be the easy part. Never got to use an airtrack at school or college.
So what? Low friction hobby wheels are dirt cheap.
Post by Dave
The difference between kinetic energy and momentum is where you've lost
most people with physics.
Nope, mostly you.
Post by Dave
Apologies for using usenet as a logbook, but there you go, don't like
secrets, and the other posters stop anything going too far off tangent.
Oh yes, science that has been well known over the entire planet for
about half millennium is just full of secrets, particularly to people
that don't understand math well...
Dave
2023-01-03 20:03:14 UTC
Permalink
Post by Jim Pennino
Post by Dave
Post by Dave
Automotive brakes: these people obviously get cars to stop. So is the
heating proportional to velocity or velocity squared?
Say a 2000kg car at 120mph (moderately high performance, not
exceptional, about limit of normal cars)
or 30mph.
30mph - 13.4m/s
120mph - 53.6m/s
at 30mph - kinetic energy is 0.5*2000*13.4*13.4 = 179,560 J
at 120mph - kinetic energy is 0.5*2000*53.6*53.6 = 2,872,960J
Don't think I'll ever get to find out anything from brakes.
That's the first smart thing you've said in a long time.
Post by Dave
However an airtrack (e.g. 12m) might be OK. How can kinetic energy be
measured?
You might start by doing some research on how the rest of the world does
it.
Post by Dave
By doing work. e.g. lifting weights. Any temperature measurement has
too many inaccuracies. Need a kit with a hook to get caught by the car
with the wire connected via a pulley to a weight stack, and hopefully a
camera to film the high point, before it all comes crashing down.
Anything electrical needs full confidence in a whole lot more other
physics.
Nope, no research and off to la-la land you go.
Lots of things to check as well like the normal hard collisions, and
soft pickup, with minimum lost energy. e.g. a paddle.

If the kinetic energy can't do work then it isn't energy. It's something
else, which I don't know about.

You should be encouraging experimental physics instead of saying belief,
belief. That's the difference between science and technology and religion.

A 60m vacuum drop is beyond my current budget, however. Anything much
less and differences between m/s^2, and m/s per meter won't be so clear.
Why are universities so scared of setting it up? Even with 9.8m/s^2 it
is good science for undergrads. Is everything looking at computer
screens now? Hopeless.
Post by Jim Pennino
Post by Dave
Giving different weights different accelerations and velocities should
be the easy part. Never got to use an airtrack at school or college.
So what? Low friction hobby wheels are dirt cheap.
Post by Dave
The difference between kinetic energy and momentum is where you've lost
most people with physics.
Nope, mostly you.
This is a follow up from over 40 years ago. At school I asked the
teacher to explain again after class, and wasn't happy with the answer.
Difference between KE and momentum.
Post by Jim Pennino
Post by Dave
Apologies for using usenet as a logbook, but there you go, don't like
secrets, and the other posters stop anything going too far off tangent.
Oh yes, science that has been well known over the entire planet for
about half millennium is just full of secrets, particularly to people
that don't understand math well...
Jim Pennino
2023-01-03 21:39:33 UTC
Permalink
Post by Dave
Post by Jim Pennino
Post by Dave
Post by Dave
Automotive brakes: these people obviously get cars to stop. So is the
heating proportional to velocity or velocity squared?
Say a 2000kg car at 120mph (moderately high performance, not
exceptional, about limit of normal cars)
or 30mph.
30mph - 13.4m/s
120mph - 53.6m/s
at 30mph - kinetic energy is 0.5*2000*13.4*13.4 = 179,560 J
at 120mph - kinetic energy is 0.5*2000*53.6*53.6 = 2,872,960J
Don't think I'll ever get to find out anything from brakes.
That's the first smart thing you've said in a long time.
Post by Dave
However an airtrack (e.g. 12m) might be OK. How can kinetic energy be
measured?
You might start by doing some research on how the rest of the world does
it.
Post by Dave
By doing work. e.g. lifting weights. Any temperature measurement has
too many inaccuracies. Need a kit with a hook to get caught by the car
with the wire connected via a pulley to a weight stack, and hopefully a
camera to film the high point, before it all comes crashing down.
Anything electrical needs full confidence in a whole lot more other
physics.
Nope, no research and off to la-la land you go.
Lots of things to check as well like the normal hard collisions, and
soft pickup, with minimum lost energy. e.g. a paddle.
If you can't understand kinetic energy, you are never going to
understand collisions.
Post by Dave
If the kinetic energy can't do work then it isn't energy. It's something
else, which I don't know about.
There is a lot you don't know.
Post by Dave
You should be encouraging experimental physics instead of saying belief,
belief. That's the difference between science and technology and religion.
Yep, but this science is about a half a millennium old and well
understood and can be found in text books, but you will have to learn
some math to understand it.
Post by Dave
A 60m vacuum drop is beyond my current budget, however. Anything much
less and differences between m/s^2, and m/s per meter won't be so clear.
Actually, such experiments are trivial to do and are done on a daily
basis from the high school level and up.
Post by Dave
Why are universities so scared of setting it up?
They are not.
Post by Dave
Even with 9.8m/s^2 it
is good science for undergrads. Is everything looking at computer
screens now? Hopeless.
Nope, only for you as you refuse to learn the math it takes to
understand such things.
Post by Dave
Post by Jim Pennino
Post by Dave
Giving different weights different accelerations and velocities should
be the easy part. Never got to use an airtrack at school or college.
So what? Low friction hobby wheels are dirt cheap.
Post by Dave
The difference between kinetic energy and momentum is where you've lost
most people with physics.
Nope, mostly you.
This is a follow up from over 40 years ago. At school I asked the
teacher to explain again after class, and wasn't happy with the answer.
Difference between KE and momentum.
So you had a shitty teacher; that's your problem.

Today there are hundreds, if not thousands of educational web sites with
videos on just about any subject you can think of.

https://www.khanacademy.org/science/in-in-class11th-physics/in-in-class11th-physics-laws-of-motion/in-in-introduction-to-linear-momentum-and-impulse/a/intro-to-linear-momentum-ap1

https://profoundphysics.com/momentum-vs-kinetic-energy-the-key-differences/

https://www.vedantu.com/physics/relation-between-kinetic-energy-and-momentum

https://www.real-world-physics-problems.com/difference-between-momentum-and-kinetic-energy.html



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