a Question About Physics in the real life , where is physics laws in the Bus ???

Hi , when you are in a bus (moving fastly) and you are carrying a stone , you throw the stone over your hands , but it don’t go back to the window and destroy it , it falls right in your hand !

now i know that the stone have the speed of us person+bus , but is there another explanation ? :smiley:


thanks , i have asked this to myself when i was 12 years old

As objects are moving, they gain momentum which causes them to continue moving until they are stopped by resistance (Newton’s first law of motion). This means that when the stone is in the air (no longer being forced forwards by the bus) it’s momentum keeps it moving at the same speed until it lands in your hand again. However, if the bus sped up while it was in the air it would go backwards as it is still travelling at the speed the bus was when you threw it.

One word: inertia. :wink: If it weren’t for this effect, the earth would move 1,000 mph under our feet every time we jumped!:eek:

thanks …

One word: inertia. :wink: If it weren’t for this effect, the earth would move thousands of kilometers under our feet every time we jumped!:eek:

i have thought of that before ,

There’s no other explanation. You got it right the first time.

It’s the way the Matrix works.:cool:

Yeah, that’s why. If you think about it, the stone was moving forwards at the same speed the bus was when you threw it up, and without anything to slow it down why would it change?

Animate it in blender, make it go up and down normally as though the bus was stationary. Then move the bus forwards at a constant speed while it happens. The stone travels in parabolas/arcs compared to the floor. Same as if you threw it forwards and up, because the things are essentially the same.

A slightly odd thing, but if you are travelling at a constant speed in the bus, it makes just as much sense to say you are travelling 50mph forwards and the floor is stationary as it does to say the bus is stationary and the floor is moving backwards at 50mph. It’s all relative, there is nothing that can be said to be completely stationary. It’s stationary relative to something else, same with the speed. Your bus is going 50mph relative to the floor, but thousands of miles an hour relative to the sun.

Things get odd when you talk about speeds nearing C though, that’s a lesson for when I’ve been awake for less than 2 days (I’ve travelled over 3700 miles today…)

At 67000 mph (around the sun) you obviously haven’t been awake long, have you now?


when you throw the stone up, it already has the speed of the bus, the air in the bus is also at the speed of the bus thus there is no air resistance, and there is no horizontal force so no horizontal acceleration or negative acceleration, thus no horrizontal loss of speed. the frame of reference of this system is the bus’s.

This can be explained in this simple way.
The Speed is relative,i will use the Simple theory of relativity by Einstein.
Imagine a ferry on the river,at the speed of 10km/h,and there are some viwers from the side of the river,and a guy running on the boat at the speed of 1km/h.

Relativity to the guys:
the boat:10km/h
the guy:11km/h

relativity to the boat
the guys that are watching:10km/h (but they are stopped)
the runner :1km/h

relativity to the runner:
the boat:0km/h
the watchers:10km/h

Relativity to the earth: (if stopped)
the boat 10km/h
the runner: 11km/h
the watchers: 0km/h

Relativity to the earth (but orbiting)
the boat: 1619km/h
the runner: 1620km/h
the watchers: 1609km/h

What this mean?
this mean that the speed is added,depending to what (to a moving object,that,if we are in,it’s static,but it’s moving)

If you throw a rock in the bus it goes down,just like if you throw a ball while moving and going at the same speed and basicly goes to your hands,the rock it falls vertically because it’s at the same speed at you,and you at the same speed of the bus.


you should not throw rocks on the bus, even if it is straight up and down. Someone might get the wrong idea, the bus driver might catch a glimpse of this flying rock in that big mirror they have, freak out, duck to avoid being hit, swerve into oncoming traffic, crash through 6 cars and one gas station before coming to rest to top of a broken gas pump and burst in to flames. You would be burned horribly except for your hand where the stone absorbed the heat and STILL would not know how you were able to catch it.

OR you could hit a glitch in the Matrix and stone really WOULD fly backwards and shatter the back window, spraying glass on to the hood of the car following too close, and THEY would swerve into oncoming traffic…

Either way, the rock stays in your backpack until you get off the bus, okay?

And dont forget our solar system is moving around AND up and down our galaxy at millions of miles per hour, and our galaxy is moving away form the center of the universe at god knows what speed, makes you wonder how quick we are travelling.

Thanks Fligh, made me smile.

It’s all relative though. There is no speed we are travelling at, except relative to something else. There is no absolute reference frame.

Oh, and there isn’t a centre of the universe.


Prove it.

There’s no absolute reference frame according to relativity, so there can’t be a centre unless relativity is very wrong.

edit - you can define the centre wherever you want, the maths still works, it’s just very, very complicated. You say the earth is the centre if you are working with satellites, you define the sun as the centre if you’re working with the solar system and so on.

Perhaps you are getting confused with the big bang?

If you think about it, when you’re standing there in the bus with the rock in hand, the rock is moving forward at the same speed the bus is, so are you. Since you and your entire system is moving as one reference frame, this includes everything in the bus. When you toss the rock up, there are no forces in this reference frame that would make it want to go through the back window or whatever (no air resistance, since the air in the bus is moving at the speed of the bus, etc. etc.). The only change in forces is vertical, the toss up and the fall down. So, since no external forces are acting on the rock, it only goes up and down. It’s like how we can stand on the earth and not be thrown about, even though we’re hurtling through space at incredible speeds (although there are many other factors that come into play there, but whatever).

edit. I pretty much just said what alot of people already did. So much for reading before I post. =P

My sister would beg to differ.
So would my ex-girlfriend(s)

depends what centre you’re looking for. the centre of mass is one of the usual definitions, and that’s a no-brainer. there are probably plenty of other ways to define a centre, most of which would have nothing to do with relativity.

there’s no reason for there not to be a centre of the universe.

@Squiggly_P: good call :slight_smile:


bah, this reminds me of trying to analyze motion in accelerating reference frames in physics.

Taking challenging classes is good. Taking the same physics class freshman year in college with a good portion of the class having placed in/won the national physics Olympiad…and not even haven had taken AP physics…slightly more questionable. my poor, poor GPA :frowning:
The professor was awesome though.
Still gyroscopes completely baffle me. I know mathematically, why they work, but there are some completely unintuitive situations you can create with them. (gyroscope precessing horizontally when attached to a rod hanging from a string, for example)

anyways, this talk of relativity made me remember what I think of as one of the more fun paradoxes.

I think its called the runners paradox, or something along those lines.
may or may not be well known. If you already know it, don’t spoil it for a little bit.

preface: an object moving close to the speed of light relative to your reference frame will appear to contract in the the direction parallel to the relative motion.

(paraphrased, and possibly botched)
A guy owns a barn, 10 meters in length with doors on either side (magic doors that can open and close instantaneously)

There is a runner, who is holding a pole 11 meters in length. This runner can run at speeds approaching the speed of light.

bar owner says to runner
“you know, if you run fast enough, you’ll be able to fit your entire pole lengthwise inside my barn”

“no way!”

“sure, just run close to the speed of light, In my reference frame, you’ll contract and be short enough to fit in the barn”

“In your reference frame maybe. In my reference frame the barn is moving at me at near light speed and it will contract, making this even more impossible.”

They agree to a test. The runner will run towards the front door of the barn at close to the speed of light. The front door is open and the back door is closed. When/if the barn owner sees that he is entirely inside of the barn, he will trigger a mechanism that will simultaneously open the back door and close the front door, allowing him to run through safely.
runner takes out a life insurance policy.

So, who’s right? Are both right? Does our runner survive? Are any doors left intact?
justify your answer.

this is left as an exercise for the reader (that phrase and its equivalent appear far, far too often in math and physics textbooks :P. That and “by inspection we see that…” ughh)

EDIT: its called the ladder paradox, or barn-pole paradox apparently. No cheating with wikipedia though!