Measure height with a watch! Cliff jump science
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- 게시일 2014. 08. 04.
- This is a simple trick using high school physics where you can measure the height of really tall objects like a cliff, using just a stopwatch.
Special thanks to Active Life Store for the GoPro shots. You can get one from them here: www.bit.ly/1y41QA2
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Here is a link to the FREE app (free as in FREE, as in I don't even have any ads in it or make any money off of it whatsoever) in the app store (sorry, no android at this time): itunes.apple.com/us/app/cliff...
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0:20 - Been stuck for minutes trying to figure out where the 16 came from. Turns out it's because he was using freedoms per bald eagle squared.
Lol
What number is it for metric?
@@markojovanovski3372 the equation he was using was:
d = 1/2 at^2 + ut, where t is time, a is acceleration and u is initial velocity.
He simplified it assuming initial velocity being 0 before the jump, leaving
d = 1/2at^2
Then, he used acceleration due to gravity (9.8m/s^2) and converted it to feet.
In metric his formula is:
d = 4.9t^2
Hope this helped
Same
@@markojovanovski3372 9.8m/s
I tried that when measuring the height of trees in a survey, sadly it took so long to complete it, because i was hospitalized for several weeks after each jump!
Silversurfer lmao
My experiment worked fine. (I threw my wife from the tree. :)
Lol throw a rock instead
@@anandsuralkar2947 r/woosh
@@nightwalker4126 lol
For all my metric fans out there, if you want to know the height in meters instead of feet, simply use d=4.9(t)^2 .You're welcome!
thanks!
simply?
WedNesdAy_GD Well, you need a calculator.
or 4.9033 for nitpicks
or gravity x time = distance
feet? how many bananas is that?
1.67 bananas
depends what size the banana is to the 48 feet. I know this is a joke but I was curious.48 feet is 576 inches so divide and this is what I got. 5 inches= 115.2bananas 6 inches=96 bananas 7 inches=82.3 Bananas 8 inches 72 bananas 9inches = 72 bananas.
1.68774 Bananas
2.97474 Apples
and 1 Cock tall XD
Donald Smith
i never joke when it comes to weird measuring units :P murica, y u no metric?
u want the D. I get it
Oh my god did you actually just do physics in feet?!
@@randomfunvideos8783 You ain't livin' till you've thrown yourself off a rock i tell ya huwhat.
@@wadurito That's no joke! I have 1 cliff jump into really cold water and a few off the side of a floating hotel/hostel in Asia. Good stuff! I'm leaving it for the more adventurous people from here on out!
scientists: REEEEEEE
Americans
Yeah. It's better than the Americans.
Just remember to account for speed of sound for bigger distances kids.
Or the speed of light...
And human processing click speed...
@@arthurmathews5554 if you see the speed of light as something to think about when measuring stuff like that then.. uhh.. idk but just dont pls xd
We know that Mr Sanders
*laughs in terminal velocity*
Note that dropping a rock and listening for the sound gets to be a little misleading as the height increases, because the speed of sound is slow enough to begin affecting your measurements. For example, if the hole is 200 feet deep the rock will take 3.5 seconds to hit bottom, but it will take another 0.2 seconds for the sound to come back up to your ears, causing you to calculate 220 feet.
I CAN'T THANK YOU ENOUGH for making this video! As an avid cliff jumper/bridge jumper, this information is extremely useful!
You can get mini waterproof laser distance tool for 40$, not for BASE but plenty accurate for diving!!
If you want meters just use 4.9(t^2). For longer falls (ignoring drag), if judge time by sound you have to account for the speed of sound which is approx. 340.29 m/s at sea level. You can get a more precise measurement quickly by dividing the initial distance approximation by 340.29 and then re-doing the estimate with the added time. At 1000 meters you will get a 26.3% more precise approximation of 854m using this method as opposed to 631m without anything. There is probably a better method but I can't think of it right now.
what happened at 2:05
"for most solid *compact* objects"
That was a good, improvised save. lol
Yeetus Defeetus yah
He probably said heavy.
It got dubbed over, he probably said the wrong thing
NANI!?
I'm glad I discovered your channel. Awesome stuff. Keep it going
brings me back to my old school days, sitting in class, listening to my baldy old professor talk cràp. you actually explain everything so much better!!
Officially the coolest science channel on KRplus
whateven except for the fact he uses feet
nice video mark :-)
thumbs up
I love math tricks like this! Thank you for sharing.
Seriously such an awesome app!! Thank you. Love your channel.
Cool way to use science
Yes.
Reniel Kun yes
True dat
6 years ago
Lol
1:58 "how bout that" 😂😂😂
So simple, yet so ingenious! I love it!
2:05 - love your games references. I particularly love that Mario 3 power.
Mark,
Can you develop an app that can convince some people around here to start jumping off cliffs, without the water of course????
Are we gonna ignore that click bait
No, we just accept that reality is often disappointing
What maybe not anymore?
No
Mark Rober timing can introduce error based on reaction time. Maybe a follow up video about measuring height (or other unknown distances) can be how to use a triangle to get the same thing with less error. I do it every day as a forester. No throwing rocks required.
Mark, you are the man. Thank you for these awesome little facts of life!
the one thing I actually remember from physics (that I’m taking now) is the kinematic stuff lol
But what if its a massive whole and it takes time for the sound to travel to your ear?
Always love your vids!
Derivation:
Assuming uniform acceleration a, the path travelled by an object is s = v_0 t + 1/2 a t^2. Now we assume the initial velocity on top of the cliff to be zero, i.e. v_0 = 0 and the acceleration is just a=g if we neglect any air resistance. This yields s = 1/2 g t^2. Now you can calculate the constant 1/2 g in you favorite units but in SI units this is about 5. So s = 5 t^2 gives a good approximation for the height if the falling time t is not too large.
Yeah, great app. My phone went dead only minutes after using it! Definitely not my fault, since _I_ just ticked the timer, jumped, swam to the bank and wanted to get the height - but the phone's dead ever since. Thanks man! -.-
+vertex rikers did you jump in with your phone...
Valerie Carrillo yeah of course - how should I be able to press the button when touching the surface, if I let the phone up on the cliff!? Duh... what a silly question! XD
+Valerie Carrillo you realize that he or she is being sarcastic right?
METRIC!!!!!!!
+trombonista92 d= (16 * (t^2)) * .3408
+Tyler McCarthy It's 0.3048, not 3408 :D
***** I did lol, I forgot to put it in. What I'm trying to say is that the answer is 0.3048, not 0.3408 :)
+trombonista92 USA! USA! USA!
+trombonista92 (9,81/2)*(t^2); Or simply just (t^2) times five.
Cool video Mark!!!!! but i have a question how do you measure the height if the acceleration is not always 9.81 meters a second. for example could this method be used for measuring the height of a model rocket?
I always learn from you Mark. Thank you
So let me see if I got this straight:
A) Download the app
B) Start the timer when you jump
C) Stop the timer when you hit the water
D) Head back to town to buy a new phone
That’s not funny. He literally said you can use any object!
@@lenchochawaka6295 WOOSH
Excellent video, as usual, Mark. Two comments: I had problems with that equations for drops with fall time measurements lower than 1.2 s aprox because of the reaction time. Typically, when you are alert and sober, your body takes like 0.2 s between the brain sending the signal and your thumb pushing start and stop.
If you start 0.2 seconds late and end 0.2 seconds late, isn't it all the same?
@@Kai-K The matter is not that you always start 0.2 seconds late. Your brain will try to anticipate. That means that it is uncertain the exact time of starting or stopping. That's why the measure time, for example, has to be reported as 1.2 +/- 0.4 s, giving you a possible value between [0.8 s, 1.6 s]. That's a possible error of 33.3%
You tube needs more up-loaders like you.
Would it be possible to change the app so that you have to hold the button down to run the timer, and let go to stop the timer? This might give you a better measurement by removing the fact that human reaction times are relatively slow.
Why did you use a thumbnail that has nothing to do with this video?
That Guy cause girl
2:07 There’s been a glitch in the Matrix
I know thought it was just me
@@systemnotifiction3346 same
Awesome video! Can't wait to test the app. I cliff jump all of the time!
Solid edit at 2:07 ... well done sneaky Rober
Oh cool, I'm gonna measure the hight of this bridge now
I wonder how many kids with this app that didn't listen to the instructions, 1: Throw their iphone over the cliff or 2: Jump over the cliff with their iphone in their hand.
If there is no gravity how come the feather and the hammer still dropped?
There is gravity on the moon.
blackboxdisease so if the astronaut jumps he wont keep on going he will come back down like on earth?
that's correct, only at a slower rate.
Jupgraded3 If there is no gravity then how is he still standing on the moon and not floating?
Great video! Thanks for sharing!
Awesome video and we'll explained. For those sad about the Imperial vs metric, in his defence most Americans understand feet far better so it is easier to market this. Plus he gave metric measurements in the app too.
One limitation to be noted: by using sound, you are delayed slightly by speed sound in the measurement, especially as heights/depths get larger, overestimating the height or depth due to this delay. Visualization is certainly more accurate if available.
Scott Wilkins - you could bang two rocks together and subtract 1/2 of the time it takes to echo out of your drop test.
'self respecting man of science' - uses feet for distance
VNDL Gday, bet u thought no-one would se this
The formula for getting feet has 16 which is a nice round whole number… the formula for meters ahead a constant of 4.9… not as simple is it…
@@zaydansari4408 Are you saying this equation in feet is simple math that you do in your head, for times like the 1.71 (he say 1.72)
Without any calculator, what is 1.71^2 ? Would multiplying that with 4.9 make you need a calculator while 16 you do all head math?
Well yeah, his demographic mostly uses feet.
Actual equation:
D = UT + ½AT²
U = Initial Velocity
A = Acceleration
T = Time Taken
Hey Mark! The cliff jump timer isn't working on the new ios. I love your videos, and if you could update it that would be amazing!
Thanks, I downloaded the app! Pretty interesting.
I WISH U WERE MY SCIENCE TEACHER , life wpuld be fun and i would learn alot at the same time :|
If you were judging the depth of something by stopping the clock when you heard the sound of it hitting the bottom, you would be inaccurate if you didn't account for the time it takes the sound to travel back up to you.
+Wes Tolson im not 100% sure here, but, at the distance where that would make a difference, air resistance would play a bigger role than it. additionally, human error is gonna play a bigger difference at reasonable heights.
Grate video! I’ve just downloaded the app, but it says that the developer has to update the app so it can run in the new iOS version. So… I hope you can release a new version of the app.
Thank you for everything!!!
Yeah, I use this approach all the time. It applies to all sorts of things. I've used it to measure distances in video games, of all things (once you verify the value of g they're using).
1:46 I dont know why this is so funny for me
"how about that" x]
I dropped a pair of scissors off my desk and got 0.38 seconds. That's 2 feet, 4 inches.
Got a tape measure, and was within half an inch with the calculation, that's pretty great lol
Im guessing the slight error is due to reaction time
@@christineyarnold5440 yep, plus 'g' (the acceleration) is not the same at all places. some places it maybe more and in others, less.
@@christineyarnold5440 I blve you must start timer as soon as you drop it. Like .5 seconds bfore itself to account for reaction time. normally it's less only, it's like .07 seconds for a drive slamming his breaks on average.
@@pkmkb it wouldn’t be too drastic a change however since it really only matters at extreme highs and lows (eg. Everest or the mariana trench)
We also need to take in consideration the velocity of sound into example where we're relying on sound of stone hitting water as velocity of sound is 874030 time slower than that of light , implying if the error will be that times too.
2:43 But there is a time delay (speed of sound) that you have to take into account. And you can only calculate that if you measure the time between impact and hearing. So you inevitably have to see the object and if you can do that anyway we can use the speed of sound to calculate the distance.
As such small distances, the time difference is in milliseconds.
0:00 so today we’re ayrere cliff jumping
😂😂😂🤣
Why would you not do physics in metric units?
because this funnily enough is simpler in feet than meters. as in this equasion 16x^2 is simpler than 4.9x^2
My son and I watch your videos nightly. Just got to this one and tried to download your app, however it says it needs to be updated to be compatible with the latest version of iOS. Thanks for your consideration in helping us solve “The Great Cliff Height Timer app Software Debacle of 2022!”
I was just thinking about this very thing this morning! Mark rules!
Now there's an AR ruler on your phone that can quite literally measure the length of an object using its cameras in real time
If you want the equation for meters it's d=4.9t²
Or you could just do the equation in feet then convert it into meters
Best video i've seen this week
Loved this video!
Damn this is super useful
Remind me to remember 16x 2 squared for the apocalypse
Me and my friend judged that the Empire State Building is 381 m tall. Rest In Peace terry
Jab jab power dunk
off by 1 meter
@@ghostderazgriz guess me and my other friend will have to do it again.
OMG I've been to that cliff jumping spot!!!! It's in arcadia!!
Sweet! Got an awesome new app!
according to my watch and my paper plane im 9 ft tall
Haha ikr
IMPRACTICAL JOKERS JUMPED OFF THAT
I come to the comments just to see if anyone else noticed it 😂
+LPSgracetv OMG I JUST REALIZED THAT!
@markrober
Can you solve this using a vertical UAM with physics?
can you explain why the equation simplifies to 16t^2? I know about the 3 kinematic equations and I have seen some equations with 16t^2 but I never knew why gravity on earth boils down to that
"How bout that?" LOL
that spider at the end must have been really big xD
I like this mainly for the idea that you integrity checked other people's videos.
I LOVEEEE your videos :) thanksss
But....
If the cliff is verrrryyyy deep, the time for the sound to travel back is increased
However, this is a great equation. Thanks Mark
In most circumstances, you don't need to hear the sound to know that the object hits the ground.
great app, but the fact that people cannot do 16t^2 is just sad.
also when you hit termial velocity doesnt this app stop working quickly for example if it takes you 200 seconds to fall from a plane this function tels you you fell 640,000ft or roughly 195,072 meters. or 195km. ie from space. although that takes significantly longer to fall from then 200 seconds.
or if you take the time it took
if you take a real life example, felix who jumped from 24miles up or 38.6km. it took him roughly 4 minutes or 240 seconds. this function says he fell from 280.904km
He mentioned that in the video, I think
***** In any case, I would really hope someone wouldn't jump off of something so high they would reach terminal velocity. Probably not good for the internal organs. Or bones.. or.. well… anything really.
***** where did you get "then" from?
Sodr7 "...although that takes significantly longer to fall from THEN 200 seconds."
mpflaherty1 oh lmao i didn't see that
Could you PLEASE update it to work with the latest iOS?? I really miss being able to use it and I was super disappointed when I was on a trip and found a crazy cliff and wanted to measure it
#28 of the binge and I love this
app isn't available anymore?!?!
Just type cliff timer and you will find it on the App Store.
Mr!. you worked in NASA and love physiscs.. PLZ! METRIC!
I think his app has metric in it. Just do 4.9 times s^2 for the metric measurement :).
@CF9417 I'm not American and I doubt that @RavnoUK is either.
@RavnoUK I think you should be knowing the converaion factor
Awsome! You are huge inspiration :D
Please update the app
I love this app!! It's fun to see all the clickbate videos😂😂😂
Um... correct my math here... but if V naut is assumed to be 0 as he is starting from rest and jumping off, and a=g=9.8 m/s^2, then the equation simplifies to d = (9.8/2)(t^2)... and 9.8/2 does not equal 16...
Now I'm not trying to be a dick... but am I wrong? If so, please explain
Kevin Petty I thought this too, until I realised that he's working in feet..
Kevin Petty g is 32 ft/s OR 9.8 m/s. UNITS!!!!!!!
+uber369 The approximation sucks
+Ceticismo.net which approximation is better? what approximation anyway?
umm... what does that mean! (i'm in fifth grade)
Metric (metres) is so much easier because you only have to multiply by 5. So square the fall time, and to multiply by 5 just move the decimal point then halve.
1 second -> 5 metres
2 seconds -> 20 metres
3 seconds -> 45 metres
4 seconds -> 80 metres etc
So you're telling me I can get people to watch a video by having a provocative yet misleading thumbnail?? Love your stuff mark!
2:05 I don´t think that an Italian plumber with a raccoonsuit can slowly fall...
*but that's Nintendo logic* XD
why u no metric
+Dave D d= (16 * (t^2)) * .3408
@@tylermccarthy7782 lol or 4.9*(t^2)
(Metres) = (Sec)^2 * 4.8768
(Feet) = (Sec)^2 * 16
Vnms - Meters: (sec)^2 * 4.9. Feet: (sec)^2 * 16.0761154855643
becouse This is America
Given air resistance, what is the fastest something could fall? And in a vacuum, would an object never stop accelerating? If we could build a vacuum tube that was infinitely high, could a dropped object reach the speed of light? That would make an interesting video...
2:14 - It would still be a good approximation of effective height, if you're only worried about just how much you're going to die, because once a human reaches terminal velocity, it doesn't really matter how much higher it is. And wikipedia says terminal velocity for a human is around 1500', so it's unlikely we'll need to measure height for anything that high without having an altimeter to do it for us (or wikipedia, if it's a tall structure). Falling from 5000' is going to be virtually the same as falling from 1500'.
2:06 “but for most *compact objects* ...”
me: watching this in 2021
“this is different”
This is only if initial velocity is 0, meaning they jump straight out. If they jump upward at all, it will say they fell farther than they actually did. This can be accounted for if you just start the timer at the peak of their jump though
I intend to jump from the cliffs of Verona Rupes, in Miranda. The cliff is about 5 to 10 km tall. I need the app updated to deal with the lower gravity of Miranda. Thanks :D
If the hole in Siberia is sufficiently deep, the speed of sound delay from the splash will result in a significant overestimate. Just saying.
yes man that's what i was thinking, for example
for a 300m deep hole, the time would be (300*2/g)^1/2=7.82s plus the delay of the speed of sound: 300/300 =1
then: (8.82)^2 *g/2=381.6
just to point it out 381.6>300, in fact that's 127% bigger that the original distance,
there is a lot of other inexactitudes in the video, as the air resistence, the real distance between the ears, the place where the object falls and where it was thrown, the fact that he took the acceleration as a constant but
a=(universal gravitational constant)*(Mass of the earth) /(distance)^2
and bla bla bla
@@juanperezmondragon1676 that comment was 4 years ago
@@littlecesarv2500 shut up
0:01 you are welcome
Thank you Mark, I now know which bridge I should jump off.
When you hear the splash, but don't see it, you need to factor in the time the sound travels.
i've dropped rocks down cliffs into mist and counted until hearing the hit to up to 13s. Thats 2700 ft, meaning sound took over 2s to come back, which is significant, and that the height wasn't quite 2700 ft.