This post is another small git tip. If you ever need to push to a remote branch
with a different name than your local branch, use
git push origin local-name:origin-name
So if you want to push your local
dev into your origin
review you’d do
git push origin dev:review
In a train yard, train cars are rolled down a long hill in order to link them
up with other cars as shown. A car of mass 4000. kg starts to roll from rest at
the top of a hill 5.0 m high, and inclined at an angle of 5.0° to the
horizontal. The coefficient of rolling friction between the train and the track
is 0.050. What velocity would the car have if it linked up with 3 identical
cars sitting on flat ground at the bottom of the track?
Hint: The equation for rolling friction is just like the one for sliding
The speed of the car after leaving the hill is equal to
v = sqrt(kinetic_energy * 2 / m)
And its kinetic energy will be equal to the work done on it:
Getting the distance is a matter of simple geometry:
d = csc (5°) * 5 m ~= 57.37 m
The force is a bit more complicated, note that I am using the net force, taking
friction into account
F = tan (5°) * 4 * 10^4 N - 0.05 * sec (5°) * 4 * 10^4 N
= 4 * 10^4 N * (tan (5°) - 0.05 * sec (5°)) ~= 1,492 N
Throwing everything together
v = sqrt(F * d * 2 / m) ~= 6.542 m / s
As the velocity will be equally divided between the cars
v = (6.542 m / s) / 4 = 1.635 m / s
Thus, the answer is 1.64 m / s.
Note that I used
10 m s^-2 for the gravitational acceleration. If you want to
be more precise, use
9.80665 m s^-2, the the standard acceleration due to
The struggle is real. Spam is here to stay, but filters have evolved a lot in
the last decade and today automatically deleting 99% (or even more) of all spam
you get is not a dream, but a feasible achievement.
I am a user of Gmail, which is a great mailing system. It gives more than
enough storage space, is very popular - what makes various applications know
how to talk with it -, and even allows for several different options of mail
viewing and filtering. There are some reported privacy issues, though, and
although I care very highly for my privacy - and the privacy of those that talk
with me -, I do not think I would be better off with my own mail server. And
the risk of those new trendy encrypted mailing systems going out from night to
day keeps me away from them.
If I ever need complete safe mail transfer, I’d just encrypt the message,
attach it and then send it through, I would have to tell the receiver the
encryption key somehow, though. Maybe I’d write the message and encrypt it in a
fresh install of a Linux distribution that never touched the Internet. I may
elaborate more on this plan in the future.
Now, back to the point and being very specific to Gmail, what is considered
spam by the Google mail service?
For your own account, Gmail learns to always mark as spam senders that you’ve
reported spam on. Likewise, it learns to not mark as spam senders that you’ve
reported not spam on.
- Dan Fingal-Surma
Simple enough, uh? You can only get spam from an address until you report it
There is also a machine learning network that collects all these manual spam
reports and makes filters for them, so spam that is reported by a few users
will never make it to the inbox of many others.
From the same engineer,
Now, if you’re the one of the unlucky first few receiving mail from a spam
campaign we know nothing about yet, spam may slip in.
This justifies those few email messages that always manage to go through the
filters. But this is a very small price to pay for the convenience of email.
Last but not least, my very nice habit of using
mailtos to my own address
everywhere does not help much to keep it away from spam senders. And allowing
who.is and similar web services to show my email address publicly is not
helping at all either, but I want it to be easily accessible to make
communication with my readers and collaborators as easy as possible. At the end
of the day, dealing with spam is so simple that it goes almost unnoticed.
I have always kept formulas and definitions I had to remember written in text
files (TXT, ODT, etc) on the cloud. Recently I decided that I should group all
these notes in the same place and make them public so that others could also
benefit from them and - why not - even help me extend them.
So I started a public GitHub repository called
formulas (may be renamed to
notebook in the future). It already has a nice level of automation, in the
sense that a single bash script triggers a new GitHub release and will, in a
matter of one or two minutes, result in a new PDF in the repository releases.
I invite you to check it out
and, perhaps, open a pull request or give me some tips and suggestions.
I wrote I would come back to write about the results of my new approach
to ticking things out of my TODO list. So let us write.
Based on my observations, tackling the most important tasks early on is
really the best way to go through your daily work, but it is awfully
tempting to do some stupid things before the most important ones.
Therefore, albeit hard, finishing the most relevant chores early on is
the way to go.
However, I have a bigger issue to solve. My lack of regularity when
going to bed reduces brutally the amount of time I have to invest each
day. I must remember that my lifespan is limited and that I do not have
all the time in the world in order to produce more in my life.
Therefore, for the next week, I am planning to write about doing the
most important things first while also being an early riser.