/sci/ - Science & Math

>>6480533
because the air in the car is moving at 70

>mfw

You probably wonder why you fall in the same spot when you jump upwards too.

>>6480543
Well yeah if I jumped up in a moving car (or your know the back of a truck or something) I would expect the bottom of the truck to have moved underneath me by the time I hit it.

I obviously have no idea on the subject which is why I'm asking here.

>>6480545
If the Earth is constantly spinning, why don't planes just fly straight up and wait for their destination to move underneath them?

>>6480550
I don't know, please explain instead of just making fun of me.

>>6480545
Closed system, conservation of horizontal momentum.

The velocity of an object only changes when a force acts on it. It keeps moving forward because nothing is forcing it to stop.

>>6480545
Because the fly by being in the car is moving 70 MPH already so when it jumps that has no effect on the momentum it already has by being in the car.
If you made the car go faster while the fly is in the air the fly would move backwards relative to the car.
I hope that helps

>>6480562
basikly wen ur on sumfing n its movign, u start 2 mov wif da objet n evenchaly ur movin at da same sped as da fing ur standin on! so wen u jump itz lik ur bein thrown by da fingy at da same sped itz movign at.

>>6480572
Ok but when the fly is flying how does it maintain the momentum when its a separate object?

i sometimes wish i was as retarded as op

wait no thats a lie.
poor fucking cunt

>>6480580
Look I know I must sound stupid but I'm looking for a proper explanation instead of just 'thats the way it is'.

>>6480578
bcuz der iz no winds or nuffing pushin da flie bakwardz n it keepz da moeshon fanks 2 newdons 1rd law

>>6480584
alright m80 cheers

The air in the car is moved with the car. This, together with what >>6480566 said, is the reason the fly can buzz around in it.

The important concepts here are momentum and friction.

If you jump on a moving truck, the momentum means you will still keep the direction you had before jumping and just add a new vertical movement (just as if you jumped out of running and just as you don't suddenly stop moving if you stop running). You would either land on exactly the same spot (if it's a closed truck) or just a tiny bit behind it (if you jumped at the back of a pickup). The first has the same reason as the fly thing, the air moves about the same way you do, so relative to you, it doesn't move. In the second case the air is not moved with the car, so you are constantly "hitting" air during your movement. Just as when you threw something against a wall and the wall stops the thrown objects movement, the air stops yours - just to a much lesser extend.

>>Go on in Part 2

>>6480599
>>Part 2

Note that without anything to stop you, momentum is theoretically kept forever. That never happens in practice, though (at least not without vacuum).

Also note that this isn't about "being part of the car", though, but about the concept of friction. If you stand on the car, friction makes your shoes "grip" to it to a certain extend. (You might have noticed that if you lay your hand on a table lightly, it's very easy to move it around on the surface. If you push it on the table with all your power, moving it to the sides becomes much harder. This is friction. As gravity constantly pulls you down, that is, towards the cars surface, you get the same effect. Maybe you think it's different, because one time you try to move and the other time the car does, but it's essentially the same. Both times you try to move one thing relative to another, and both times the fact that both things are pressed together causes friction, which keeps the two object together). Anyhow, even though friction keeps your shoes gripped to the pickup, the air still doesn't move. so you are still constantly "hitting" air, which slows your movement. On the other side the friction between you and the car pulls you with the car though, so while the air makes you slower, the cars friction makes you faster. If the air was thicker (would stop you more) or the car was slippery (less friction) the air would overcome the friction, and you would practically be blown off the car. The same happens a bit if you jump: The friction is lost, and as long as you are without contact to the car, the slowing of the air decreases your speed of movement, effectively letting you land behind where you jumped.

Hoped that answered your question, anon.

>>6480599
>The air in the car is moved with the car. This, together with what >>6480566 said, is the reason the fly can buzz around in it.
Correcting myself, it's actually not "together with what anon said", but "exactly what anon said".

>>6480533
"A car is moving at 70 kph and a pendulum is supended from the ceiling. Because the car is moving at a constant speed, the pendulum hangs down perpendicular to the ground"

A physics problem starts like this. A female student (first semester) remarked that because the car was moving, the pendulum does not hang perpendicular, but, in fact, at an angle of "about 70 degrees". We refer to her as "70 degrees".

>>6480533
Everything in the car is moving at the same speed as the car. That's why seatbelts are such an important safety measure.

OP is 5 years old :^)

>>6480572
wrong. If I throw a baseball out of a car (an area where the wind is shielded from) it will instantly have another force act upon it other than gravity and velocity -- the wind. If one were to jump from the back of the car (where wind is shielded from) straight up out of the shielded area, it's possible to be pushed by the wind enough to a) throw he or she off balance b) be pushed back far enough to stumble over the back, and if the wind is strong enough c) pushed off entirely.

>>6480533
Because you, the car, the air inside the car, and the fly, are all moving at 70 MPH forward. The seem to be "stopped" in relation to each other, because they are going at the same speed relative to the ground, for example.

If, however, you were to suddenly accelerate from 70 to 200 MPH, you would feel your body pushed against the seat, and the fly would also be thrown backwards.

>>6480996
why would you even respond to somebody who types like that. i mean with words, of course, euthanasia would be a perfectly suitable response.

Holy shit, /sci/. Didn't know most of you were such cunts.

>>6481028
>Holy shit, /sci/. Didn't know most of you were such cunts.

Only when you ask a dumbass question a 12 year old would ask that could be easily solved by a five second google search

See:
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
http://en.wikipedia.org/wiki/Inertial_frame_of_reference

>>6480533
Here's some full answers.

>Why does the fly stay stationary inside the car as the car moves?
Because the the car, and the air inside it, and the fly, are all traveling at the same constant velocity.
Because of Galilean (or Lorentz, if you're doing special relativity) invariance, it makes no difference whether the car is "stationary" or "moving." In fact, those terms don't make sense until you specify a reference frame.

>the second the fly leaves whatever surface its on, it should fly straight backwards?
If there were no air around the car, then the fly would keep going at the same forward velocity.
However, because of the air outside of the car, which (from the car's point of view) is rushing backwards, when the fly gets out of the car, the air resistance will instantly start to act against the fly's movement.
I'm also ignoring the effects that the car itself may have on the air outside of it, and I'm assuming that the air is stationary with respect to the ground (i.e., there's no wind).

>>6481028
>be on 4chan
>be surprised that people are rude as fuck
>be a total faggot
>be new here

pick all 4, dude.

These fucking threads.

>>6481090
Good job, you really showed OP! Do you feel better about yourself now?

>>6480566
where does the momentum-energy come from?

>>6481104
the Big Bang.

>>6481099
I kinda do, you see this has been the best laughs today.
pick related, me currently.
Not full blown hysteria but certainly stronger than mild giggles

>>6481110
Maybe, you could've, ya know, contributed?

>>6481114
And ruin the fun?
Besides the question was answered correctly several times already starting from surprise surprise first fucking post.
I think that just adds to the fun factor massively.

>>6481104
Momentum isn't a kind of energy. It's just a word describing the fact that motion energy is not lost the moment the cause of a motion (the force) stops. In fact, no kind of energy is lost without being transformed into some other kind of energy. Your motion energy becomes less because it is transformed into heat energy when you hit the air (Ever seen a movie where a space ship starts to glow hot upon entering the athmosphere? That's motion energy being transformed into heat, with the typical hollywood inaccuracies). Also a part of your motion energy is transferred to the air itself.

To your question where it comes from, >>6481106 is actually a decent answer. The energy the big bang produced still exists, in heat and motion energy, and many other kinds, including mass (e=mc2).

In the case of the moving car, the energy stored in the oils mass is set free due to a chemical reaction (it's burnt) and transformed into heat. That heat increases the pressure in the motor, moves it's parts and thus partly transformes itself into motion energy (a big part is just going somewhere else without being transformed, or is just transferred to the motor itself, which is why a running motor and the air around it is hot). The motion energy of the motor is brought to the wheels (only partly again, the rest is transformed into heat again due to friction), and from there is used to move the car itself with the help of the floors friction (also a part of it is transformed into heat again, so the road becomes warmer). Keep in mind that while coloquially you may say the energy is "lost", it isn't in the physical sense. It's just not transformed and transferred in exactly the way you would ideally want it too.