If you run 10mph inside of a train that is moving 100mph, are you moving 110mph or 100mph?
In: Physics
You are moving 110 mph relative to a stationary observer on the ground, and 10 mph relative to a stationary observer on the train.
Velocities are all relative to something – am I standing still, or am I moving at 107,000 km/hr relative to a stationary observer on the sun?
Like running from the back of the train to the front of the train? You would be moving at 110 mph relative to the ground.
To imagine this, if you and your friend were on the same train at the back and you started running to the front while they stayed sat at the back, your body would enter the next train station sooner than your friend who was still at the back. Your velocity would be slightly faster.
Context is everything.
From the perspective of the station, 110mph.
From the perspective of a passenger, 10mph.
From the perspective of the sun, roughly the speed of the earth’s orbit.
From the perspective of a bead of sweat on your body, not at all
Velocity is all relative to where you’re looking from. From the perspective of someone standing on the ground outside the train, if you run in the direction the train is moving, then you are moving at 110mph. (90mph if you run against the train). From the perspective of you and other passengers on the train, you are only moving at 10mph. From the perspective of space, if your train was travelling east along the equator, you’d be moving at 1,110mph, because you and the train are travelling along the direction of Earth’s rotation (which is approximately 1,000mph at the equator)
If this were an elementary physics problem you’d be solving from the perspective of the person watching the train from the outside.
Ah yes. It depends on your reference point. Compared to the train, you are traveling at 10 mph. Compared to the ground, you are traveling 110 mph.
Compared to the pen in your pocket, you are standing still.
Compared to the guy standing at the North Pole, you are traveling at 800 mph.
Compared to the sun, you are traveling (guessing, because I’m too lazy to look it up) 20,000 mph. Compared to the galactic center, you are traveling 100,000 mph.
Relative to the ground, you are travelling at 110mph. Or 90mph. Or a speed somewhere between 90 and 110mph. Running direction is important too.
You are moving 10mph compared to the train.
You are moving 110mph compared to the train tracks.
It is called frame of reference.
To an outside observer, witht he train moving 100mph, you walking inside would be walking at 110 miles an hour, but to YOU inside the train doing the moving, you are moving at 10 Miles an hour.
Same for the ISS. It orbits at 17500 Miles an hour, but are the astronauts traveling at 17500 miles an hour ?, YES, but inside the ISS, they move about at normal speeds. Again, it is Relative to the observer.
Observer on the ground looking up, or looking inside the ISS ?
This is a perfect opportunity to explain relativity and relative motion!
Because it all depends on your point of observation.
To a person on the train with you, you’re moving 10 mph.
To a person standing beside the tracks, you’re moving at 110 mph.
To a fixed point in the solar system, you’re moving 110 mph PLUS the 60,000 miles per hour (or something like that) that the earth is traveling around the sun, plus the tangential rotational speed (which varies depending on lattitude).
From a fixed point in the universe you’re moving 250,000 miles per second or something like that, as the milky way galaxy hauls ass through space…
Numbers are wrong, for sure, but you get the point, which is *all motion is relative*. Without a reference point, you can’t even establish that motion is even occurring, and all motion depends on the relative motion of you from that reference point.
So the answer is yes, depending on perspective, both conclusions are perfectly correct.
Your velocity, relative to the train is 10 mph.
If you’re running from the back towards the front (i.e. in the direction of the train’s motion) they add to give you 110mph.
If you’re running from front to back, you’re travelling 90mph.
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