74 Replies to “Pencil In The Water Illusion”

  1. Refraction 101:

    Light actually travels at different speeds in different mediums. In thi situation light travels slower in water than it does in air and this difference causes the light to bend.

    Imagine a car driving along a road and suddenly its left wheels hit sticky tar, it would turn left as its right wheels are moving quicker than the left until the right wheels too hit the tar and match speeds resulting in the car now moving in a straight line.

    That is the boring physics explanation from what I remember.

    -Teh Hamsteh

  2. OMG!!! I am in the 8th grd. and my seven year old cousin just did that she put the pencil on the outside of a glass full of water and it did the same effect!!!!

  3. I’ve known that objects appear bent in water since I was like 7. I learnt why it did that about 5 years later.

  4. oh for cryin out loud, science people science! Light refracts (bends) through the water a bit like the science experiment that you did at school where you set the spot light up and put a glass triangular prism infront and watch the light come through at a different angle!


    Let me explain.You first get a glass of water.You then find a highlighter inside.What you see is the highlighter in the water is bigger than the part sticking out.Then pull it out.It converts back.Its awesome.

  6. itz not in 6th grade itz in fifth duh rite at the begginnin omg cant u do SOMTHING about ur memorie FARTED purleeeeeeeeeeez light refracts…duh….like in hatchet wen he’s tryin 2 fish w/ a pole…gawd itz not an illusion at all……..itz science…..thank u everyone EXCEPT FARTED WHO IS DUMB CUZ IF UR IN 6TH U SHOULD OF LEARNT IT LAST YEAR DUHHHHHHH

  7. water has a positive refraction index so thats why it bends like that

    if u guys cant understand this i really want to see what happens when you see a substance with a negative refraction index (it would make the pencil appear above the water)

  8. bla on,
    sum schools teach it early, sum late,
    depends where you go.
    in ireland we dont call it grades or year 1
    we call it first class (primary sch.) first year (2nd sch.)
    im goin into 2nd year and i didnt even learn that in school,
    didnt u ever ask ur parents stuff
    u disgust me,
    all of u

  9. My knowledge of the properties of light is limited, but I know for a fact that light always moves at a constant speed, no matter the medium (provided that the medium is at least somewhat opaque). So, therefore, Tehhamster, it can not be due to speed of light. (even if it does change the speed, it does so very minimally, it is negligable).

    It is due to the refraction of the light due to the curved shape of the glass.

  10. lool, i’m in year 9 (no idea what grade you americans call that, i’m 13) and we learned about refraction last term. The thicker the glass the bigger the refraction and the more displaced it is.

  11. right…. light DOES travel faster in air than water, roughly 1.5 times faster, hence the refraction index of air=>water is 1.5 ish. but actually coz the light is coming out of the water (and through glass actually) the refraction index is 1/1.5. (well actually 1.02 coz that’s the refraction index of air). David, if you want to know what a positive refraction index looks like just imagine the air is water and the water is air. turn the pic upside down! the only way you can have anything with a negative refraction index is either if you’re looking through a vacuum in air (unlikely) or if you are underwater and see an air bubble or whatever – the inde is the ration of the speeds of light in the two media, to get a negative one it has to be slowing down. so light coming out of water has a positive refraction index light going into water from air has a negative refraction index.

  12. ok if he/she is in 6th grade or 7th now w/e grade (u r in) don’t make fun of him/her! i mean it’s a kid 4 cryin’ out loud!

  13. OMFG people just calm down already! Just because something has a simple explanation doesn’t mean that it isn’t still an awesome thing. I went over this kind of stuff in 2nd grade but I still like to look at it because it is cool.

  14. teh hamster is almost right, light travels at differents speeds through different mediums. when going through a denser mediam it bends towards the normal. the normal is the imaginary verticle line. i’m in 9th grade and about to do an optics lab after my midterm in honors physical science.

  15. you science guys are all mentaly retarded. its so simple, it’s not even worth explaining to these idiots. light refacts when going through a medium with a different density. in this case the water is more dens so the angle changes to be closer to the normal. thats the anwser from a 14 year old who actualy knows the real anwser. (adults are old and stupid and little kids are annoying)

  16. ok, 2 things:
    Light doesn’t bend, it changes direction; light only travels in a straight line, so ‘teh hamster’ you’re right in so far as it refracts due to it slowing down, but wrong in so far as it bending,

    2. David, you can only have a positive refractive index, you can’t have a negative refractive index, as the lowest refractive index is 1, which is a vacuum.
    so you’re all silly and obviously didn’t listen too well in physics.

  17. ok, Mr. ok, 2 things, here’s another 2 things:

    1. General relativity theory might disagree, particularly with reference to gravitational lensing. Not that a glass of water has a large enough mass to make this noticeable. It does make you wrong, however;

    2. The range of the refractive index function is in the domain of positive real numbers, and may well be between 0 and 1. Negative refractive indices are (theoretically) possible, though probably do not occur naturally.

    Allow me to add arrogant to being silly and not listening.

  18. well i daint learn dat refragment stuff n i neva new how it worked til dat hamsta dude sed bu yea im in yr 8 lol das bad huh? erm mayb i did i was jus asleep dat day lol

  19. woot grade 6 science… or whatever the grade u learned it in no one cares dont show off we all get it
    awsome keep on posting


    And I am very sorry to say it.

    But SERIOURLY, when was the last time you people had a drink with a straw in it???

    But there IS something interesting you can do with this effect- I discovered it when I was seven, with a pokemon superball I used to have. Try it.

    1. Take a ‘bouncy ball’, ‘superball’, transparent sphere or just something clear with a curved surface- but it MUST have an object inside- like a little toy or a preserved beetle or something.

    2. Put it under water

    3. Notice how the object appears to SHRINK. You are actually seeing the object at its ACTUAL SIZE, but the curved surface magnified it, until the water stopped the effect.

    cool eh? EH?

  21. WTF people ok sure there is a scientific explanation to it it is just a neat thing that vurdlak wanted to share, and + u ppl that r telling others that they r stupid, U r stupid bcus the only reason u r doing it is to feel bigger, bcus u r insecure so how bout u SHOVE IT!

  22. They aren’t stupid. they just don’t know. =/
    I bet you don’t know many things, would you like it if people called you stupid?

  23. omg!U guys, who cares.I did that b4.so wat i still like it!come on,people havnt tried this yet, is still learning.And i think that was amazing!

  24. I think it’s hilarious that Anonymous thinks adults are stupid, especially considering that WE learned the same things in school, too!!! ACTUALLY, I was going to agree with almost everything he said, until I read this: “1.
    Light doesn’t bend, it changes direction; light only travels in a straight line… but wrong in so far as it bending,”
    LIGHT DOES BEND!!! THAT’S THE WHOLE POINT OF REFRACTION AND NEGATIVE REFRACTION! That’s why scientists are using copper as a means for invisibility cloaks! Who’s the stupid one, now, silly thing! Since I probably won’t be using this site again, everyone have a nice day and please refrain from calling names and using profanity…after all, you’re KIDS!

    1. Everyone has there own way of thinking…
      be more considerate and think for other people around you instead of making people feel bad…get a life douche

  25. oh and, khamani its an easy mistake to make, when “cross your eyes” then the refracted section looks closer to the normal line

  26. the first sentence says REFRACTIVITY of water.
    learn to read to all those idiots that said it’s just refraction.

    1. Here’s the thing;
      conductivity = adjective(describes a quantity) conduction = noun
      conduct = verb.

      Same thing with refract, refractivity, and refraction. Please don’t flame others comments unless you truly know what you’re talking about.

    2. the verb-adjective-noun thing is correct but I think the point that anonymous was trying to put across is that it already says in the article that it is the refraction of the water. But why are we arguing about grammer anyway?! this site is for illusions!!!

  27. Back off this guy! He’s from Croatia, and though there are some mistakes, he employs a mastery of the English language that many Americans can never hope to achieve.

  28. forget all about ppl not knowing about refraction. have you guys noticed that the master with ‘fields of knowledge in “physichs” and maths’ can’t spell PHYSICS

Leave a Reply

Your email address will not be published. Required fields are marked *