Visual interpretation of the cross product and the dot product of two vectors. My Patreon page: / eugenek
Пікірлер: 680
@EugeneKhutoryansky5 жыл бұрын
To see subtitles in other languages: Click on the gear symbol under the video, then click on "subtitles." Then select the language (You may need to scroll up and down to see all the languages available). --To change subtitle appearance: Scroll to the top of the language selection window and click "options." In the options window you can, for example, choose a different font color and background color, and set the "background opacity" to 100% to help make the subtitles more readable. --To turn the subtitles "on" or "off" altogether: Click the "CC" button under the video. --If you believe that the translation in the subtitles can be improved, please send me an email.
@ikrishna063 жыл бұрын
I like your explanation 😉😁
@jollyriju29192 жыл бұрын
I can't find gear symbols under this video
@NicksDomain1017 жыл бұрын
I love the terrifying climax of the music when they show the hand
@ToLearnDev7 жыл бұрын
it makes me scared of math
@Floppylikescheese7 жыл бұрын
It's like they showed the ultimate universal secret. It's in the HAND!
@MatomeQuestMoremi7 жыл бұрын
NicksDomain101 Yup. Excellent but awkward.
@Bemmu7 жыл бұрын
Thanks, I spilled my drink laughing at your comment.
@user-bv6bi2sz8r7 жыл бұрын
This music makes me feel like I am some Mathematicians thinking hard of a very tricky problem in 18th century.
@rmsvideos13357 жыл бұрын
Came for cross product, left with existential crisis.
@pipturbine4736 жыл бұрын
Hahaha legend
@thanhvinhnguyento70696 жыл бұрын
RMSVideos oh god
@arpitjohri97435 жыл бұрын
Same bro, same
@robinranabhat31255 жыл бұрын
legend
@vivekstreme19944 жыл бұрын
Lol
@SirBagelFace4 жыл бұрын
This video has such an ominous energy and I was not prepared for it.
@ProGaming-kb9io5 жыл бұрын
The music is like: Harry Potter and the Vectors calculations chamber.
@RedFox-dj7di4 жыл бұрын
XD
@anu_17023 жыл бұрын
ROTFL
@edgbaston1493 жыл бұрын
True
@ishworshrestha35593 жыл бұрын
Ok
@danieljoseph26477 жыл бұрын
the ending song was perfect
@marco_robert3 жыл бұрын
1) A very clear and understandable diagram 2) Great way of animation. 3) Awesome way of teaching. 4) A good mound of effort 5) Subtitles in all languages.. And much more!!! I can't just thank you enough. Thanks to help and guide...
@EugeneKhutoryansky3 жыл бұрын
Thanks for the compliments.
@danielstewart3507 Жыл бұрын
Marco, 4) Amount of effort. Not mound of effort.
@marco_robert Жыл бұрын
@@danielstewart3507 Yeah 😅
@belliumm8 жыл бұрын
Eugene, I don't think you'd ever expect to hear someone say this, but your videos have helped me fight depressive thoughts and anxiety. I was once caught in an deterministic perspective on the world and lived a life thinking my existence had little impact. Then I stumbled upon your quantum mechanics video and it gave me so much hope and wonder. I realized still have so much more to learn about this reality and that our very existence impacts the world around us. Your videos explain sciencific concepts incredibly well and make them so interesting you have actually made me consider taking up a career in physics. Thank you, I appreciate your work greatly. You have impacted my life and brought out the inner child in me.
@EugeneKhutoryansky8 жыл бұрын
+Aquas Studios, I am glad to hear that my videos have had such a profound influence on you. It is nice to know that my work is having a positive impact, and thanks for the feedback. To the best of our knowledge, according to quantum mechanics, it now appears that we do not live in a deterministic universe. I plan to soon have several more videos dealing with quantum mechanics, and I hope you will enjoy them too.
@allankaige73645 ай бұрын
Hows it been going for you? Its been 7 years. I hope it's all gone very well.
@belliumm5 ай бұрын
@@allankaige7364 It's been good, I went on to get my bachelor's of science in computer engineering. At the time I was a high schooler that was going through a little existential crisis.
@MDMAx4 ай бұрын
@@allankaige7364 +1, @belliumm, where has your curiosity taken you?
@peeyush828 күн бұрын
How’s it going now brdrrr
@ccd73396 жыл бұрын
the song perfectly matched the topic=terrifying
@elijahizere8 жыл бұрын
The music was shocking, put some humorous light on this video. Loved it :P
@mgtowindia95494 жыл бұрын
She was serious
@wurttmapper22007 жыл бұрын
If you are wondering, the name of the song at the end is called William Tell Overture by Rossini. Please listen up the long one and not just the finale
@LuRybz8 жыл бұрын
extra: if the result of the cross product is 0 (null vector), you have two parallel vectors if the result of the dot product is 0, then you have two perpendicular vectors God Bless you all.
@TheIsrraaa7 жыл бұрын
Known as orthogonal vectors too :)
@ashishkumarsharma13235 жыл бұрын
If both of em are zero then?
@Ghost____Rider5 жыл бұрын
@@ashishkumarsharma1323 they both cannot be zero
@rishitasf5 жыл бұрын
Oh thanks...
@johnrubensaragi41254 жыл бұрын
@@Ghost____Rider of course they can, if one of the vector is zero
@sy_ox6 жыл бұрын
3:53 when you finally realize you are One with the force.
@EugeneKhutoryansky8 жыл бұрын
If you like this video, you can help more people find it in their KZbin search engine by clicking the like button, and writing a comment. Thanks.
@matthewburson29086 жыл бұрын
I like that this was voiced over by an anime voice actress.
@Derick_2865 жыл бұрын
Physics Videos by Eugene Khutoryansky use less
@Derick_2865 жыл бұрын
@@Higgs314 then what should i say?
@meenumeeny995 жыл бұрын
BGM is so irritating
@sushilghildiyal93194 жыл бұрын
@@Higgs314 They have taught, dot product wrong, dont just believe all youtube videos
@kevinz11ca8 жыл бұрын
the ending music is so epic!
@EugeneKhutoryansky5 жыл бұрын
You can help translate this video by adding subtitles in other languages. To add a translation, click on the following link: kzbin.info_video?v=h0NJK4mEIJU&ref=share You will then be able to add translations for all the subtitles. You will also be able to provide a translation for the title of the video. Please remember to hit the submit button for both the title and for the subtitles, as they are submitted separately. Details about adding translations is available at support.google.com/youtube/answer/6054623?hl=en Thanks.
@akshatmandloi32784 жыл бұрын
Please make video on constraint relation
@cphVlwYa8 жыл бұрын
It's the best thing when I am searching for an animation and find my way back to this channel :) They make everything so much easier to visualize and understand
@abhishekbhattacharjee46397 жыл бұрын
i didn't expect such good use of music in a physics vid .....great job
@heliosaeon14586 жыл бұрын
shadow claw But this is basically maths.
@Artaxerxes.5 жыл бұрын
This is math you moron
@1mursyid17 жыл бұрын
that moment when this 4 minutes video taught me about vector better than my 1 hour physic lecture....
@fazaldudha57287 жыл бұрын
Loved the graphics along with blasted music to make sure viewer is attentive. Speaker voice gets the vote too!
@imme_fr3 жыл бұрын
the most dramatic educational video on youtube.
@mikkolodeon70535 жыл бұрын
Still dont get the idea behind the Dot and Cross product.. I'll just memorized the formula, then solve the problem, get an A+, never asked why, and go on with my life..
@uathrhsalim5 жыл бұрын
Every student ever .
@OneDerscoreOneder4 жыл бұрын
and then forget it a year or two later*
@cinquine14 жыл бұрын
Me, until it became important. Then I had to go back and actually learn it :/
@ericklestrange62554 жыл бұрын
all hail youtube for actually explaining shit
@Dragoneer3 жыл бұрын
@@cinquine1 Same, I'm studying a degree in engineering and we're looking at the cross product between instantaneous angular velocity and perpendicular radius to find instantaneous linear velocity, and I have just realised are perpendicular to each other vectorially. So I guess I _do_ have to know about cross products after all! I was thinking to myself, "goddamit...." Although..I've now found out it makes the whole process sooo much easier to understand calculating this all _vectorially_ using numerical unit vectors rather than taking a geometrical approach using their magnitudes instead (lots of confusing lines and trigonometry :/ )...which is why nowadays I'm actually starting to appreciate cross products a lot more than I had done in the past. That's something I never thought I'd say cause I found them hellish to understand in further maths. But they're actually fairing out to be _extremely_ useful when finding perpendicular magnitudes that are in a three dimensional space with each other...such is the case with angular motion. You just have to know about this fact beforehand. All you have to do is arrange two perpendicular vectors in a matrix with their unit vectors above, and find the determinant of this, for a third vector that's perpendicular to both. After that I was wondering why tf I never did this in the past cause it was so straightforward compared to how I was doing it with trig... Saves time learning a bunch of different formulas when all you have to know is that (with unit vectors) : i = j *x* k ; j = k *x* i ; k = i *x* j ; and they are not commutative, so the reverse is the negative of those. Eureka moment for me XD (please tell me if I'm wrong about this :S )
@TDBRICKS2 жыл бұрын
Super helpful. Thank you!
@EugeneKhutoryansky2 жыл бұрын
I am glad my video is helpful. Thanks.
@sharonjoe7535 Жыл бұрын
You here?!
@HyperDevv3 ай бұрын
WAIT TD BRICKS HERE?
@missakissa9876 жыл бұрын
Hahahahhaha I cracked up so hard when the dramatic instrumental music came when revealing the cross product direction. Never thought such an informative thing would do that. Now I'll definitely replay that moment in my head during the exam.
@Test-ri2kr3 жыл бұрын
This is a fantastic video! No waffle. Not too slow, not too quick. Just perfect. Thank you for these amazing videos. They help me visualise what the hell is going on underneath all those ridiculous maths problems I solve haha 😅
@EugeneKhutoryansky3 жыл бұрын
Thanks for the compliments.
@zEre3263 жыл бұрын
I'm a very visual person and could not understand why we use dot and cross product!!! this video literally saved me thank you !!!!!
@EugeneKhutoryansky3 жыл бұрын
Glad my video was helpful. Thanks.
@SteichenFamily8 жыл бұрын
Your other videos have been very explanatory. I like that they assume a novice viewer. Unfortunately I'm not following this one. It might help if you could detail some applications...like the time/speed/distance application in your calculus video, that made it clear how such a thing is used.
@flamestorm066 жыл бұрын
Thank you, I was having a lot of difficulty in understanding the right hand rule, that demonstrated it perfectly!
@fakherhalim8 жыл бұрын
This is the best illustration humanly possible!
@EugeneKhutoryansky8 жыл бұрын
+Fakher Halim, thanks for the compliment.
@shipwreck91464 жыл бұрын
I have been doing dot products for years now, no professors have ever explained it this well, and I think visually, so because no professors explained it, in my head I always said it was "how much the vectors are of each other." But this video helped me understand so much more.
@EugeneKhutoryansky4 жыл бұрын
Thanks for the compliment about my explanation. I am glad it was helpful.
@_AnmolGupta3 жыл бұрын
From the last 3 years I am studying about DOT and CROSS product but I today visualize it.. That's very nice and useful video... Thanks alot...
@EugeneKhutoryansky3 жыл бұрын
Thanks. I am glad my video was useful.
@samirkhosrowshahi79288 ай бұрын
This is the absolute best video I've ever seen that defines the dot product. All of the conceptual stuff that other videos try to explain pales in comparison to the simplicity of this visualization.
@EugeneKhutoryansky8 ай бұрын
Thanks for the compliment about my video.
@tpespos8 жыл бұрын
Don't stop you keep blowing my mind with simple stuff I have been using cross products for years and never realized it was just the area between the vectors
@EugeneKhutoryansky8 жыл бұрын
+tpespos, glad you found this interesting. More videos are on their way.
@MAG_104 Жыл бұрын
This might be one of the most terrifying videos I have ever seen. When the music climaxes at the hand my heart dropped into my gut.
@b43_pranjalvyas765 жыл бұрын
This was so superb....at the end of the video I felt dots connecting in my brain and at the very same moment the music was playing in the background!!!
@jhoan71894 жыл бұрын
perfect illustration of complex vector subjects. thank you!
@ashutoshpatel50306 жыл бұрын
sir you provide absolutely concept that others do not....it awesome....I loved it
@EugeneKhutoryansky6 жыл бұрын
Thanks.
@KushG4202 жыл бұрын
aren't you a blessing. Humbly grateful madame Eugene
@EugeneKhutoryansky2 жыл бұрын
Thanks.
@flare9098 жыл бұрын
I've been waiting for this video forever!!!!!! Thank you!!!!
@EugeneKhutoryansky8 жыл бұрын
+flare909, the wait is finally over. Glad you liked it.
@jocomo50542 жыл бұрын
I just searched for a demonstration Thank God this video recommended for me
@EugeneKhutoryansky2 жыл бұрын
I am glad you liked my video.
@angeldavidstarrmauas83223 жыл бұрын
Amazing! Finally I get to understand this! The single best explanation I could even fathom! Just awesome! Thanks so much!
@EugeneKhutoryansky3 жыл бұрын
Glad my explanation was helpful. Thanks for the compliments.
@MathFortress8 жыл бұрын
More on the cross product: kzbin.info/www/bejne/oKGulKOpg6yafNE
@cloudyclo6 жыл бұрын
Thank you so much!!! I've been struggling to visualize the dot product and cross product for the longesttt time. This animation helped me so much! As well as the circuit video I saw the other day!
@EugeneKhutoryansky6 жыл бұрын
Thanks. I am glad my videos are helpful.
@cloudyclo6 жыл бұрын
You know, in high school I've always dreamed about how great it'd be if there were people knowledgeable about physics who could also animate complex topics they were discussing because there are some things that are hard to visualize. Can you imagine how cool a physics and animation major would be? :) There's also a lack of animated physics videos, but here you are animating physics videos very well and fulfilling one of my dreams! :D I'm very proud of you and the work that you do, and I'm forever grateful. I wish you the best in your endeavors. :)
@StevenKarma8 жыл бұрын
Your explanations are always very clear. Please continue making videos!
@EugeneKhutoryansky8 жыл бұрын
+Steven Karma, thanks for the compliment. More videos are on the way.
@etherealbae21605 жыл бұрын
This was.. memorable. Thank you!
@lightoftheFather_3 жыл бұрын
This is the best explanation on KZbin!
@EugeneKhutoryansky3 жыл бұрын
Thanks for the compliment about my videos.
@Feynstein1008 жыл бұрын
Great explanation, Eugene. Can't wait for your next video.
@EugeneKhutoryansky8 жыл бұрын
+Feynstein100, thanks. Glad you liked it. I am working on my next video, which will be on Quantum Wave function visualization.
@TheRabidCabbage5 жыл бұрын
I watched a bunch of videos on this subject and this was the first that made sense.
@amritpatra68573 жыл бұрын
Wonderful video recommended by my physics teacher pure gold
@amritpatra68573 жыл бұрын
Killer visulaisation
@EugeneKhutoryansky3 жыл бұрын
I am glad you liked my video. Thanks.
@amritpatra68573 жыл бұрын
@@EugeneKhutoryansky welcome Ma'am
@chhavigupta28027 жыл бұрын
so good thanks a lot...wished I knew about ur videos earlier. I wouldn't have faced any problem then...
@EugeneKhutoryansky7 жыл бұрын
Thanks. I am glad you like my videos.
@IamArob0t6 жыл бұрын
that plot twist music at the end was perfect
@basitsultan28544 жыл бұрын
Superb 💖 touched my heart.thankyou so much.keep it up 💐
@EugeneKhutoryansky4 жыл бұрын
Thanks.
@shafiqreshid42882 жыл бұрын
Underrated video with an OG climax
@parjohansson31188 жыл бұрын
Another beautiful visualization! These videos should be used in college as well as in universities!! And, for totally unknown reasons, I would like to see a behind-the-scenes. Making videos like this must be a daunting task.
@EugeneKhutoryansky8 жыл бұрын
+Pär Johansson, thanks for the compliment. I would have to think about how to do a behind the scenes video. Thanks again.
@bloggervista8 жыл бұрын
When i heard the title of video i remembered the video about electromagnetism and gyroscope i guess :) Thanks eugene . Without you i would have stuck in physics very badly :)
@EugeneKhutoryansky8 жыл бұрын
+Shirshak Bajgain, glad to hear that my videos have been helpful. Thanks.
@smitititecnosoft4 жыл бұрын
I started understanding the behavior of universe by the concept of your videos.. thanks.
@BrunoSdeLima6 жыл бұрын
Fantastic. These tools are priceless for students!
@AlmightyXI3 жыл бұрын
Wow I hadn't seen this link between particle handedness before now. Glad I found your channel
@Leo-sh1ih8 жыл бұрын
As a visual learner, thank you for this awesome visual explanation!
@EugeneKhutoryansky8 жыл бұрын
+roux ga roux, you are welcome, and thanks for the compliment about my explanation.
@dariocardajoli68312 жыл бұрын
There are no visual learners. Periodt.
@ollllj8 жыл бұрын
this may be trivial to many, but to me, who only needs to remember crossproduct and dotproduct basics every 5 years or so, not doing vectors in that much detail usually using a blackbos, its easy to get your memories confused without such good visualization.
@MunchyMallow6 жыл бұрын
The dot product visualization exploded my brain. I never knew it was this simple.
@Pri-tf9iv8 жыл бұрын
this video was soo needed!! thank you sooo much!
@EugeneKhutoryansky8 жыл бұрын
+Arpita Singh, you are welcome, and thanks.
@sukanya34112 жыл бұрын
Music gave me flashbacks to the funeral of my great-grandfather, back in the Victorian era. Man those were some sad days.
@leyre99897 жыл бұрын
Thanks so muuuuuch!! I already understood the dot product but i couldn't visualise the cross product so this has been soo useful :)
@EugeneKhutoryansky7 жыл бұрын
Thanks. Glad to hear that my video was useful.
@ryanw.49834 жыл бұрын
This really helped my understand this concept! Thank you!
@EugeneKhutoryansky4 жыл бұрын
Glad my video was helpful. Thanks.
@nandikakaul69794 жыл бұрын
Wow. This was so helpful! Thank you
@Muuip4 жыл бұрын
Great visualization! Much appreciated!
@EugeneKhutoryansky4 жыл бұрын
Thanks.
@sethconnell34978 жыл бұрын
I just found your channel today. I think I'm going to be a lifetime subscriber. :]
@EugeneKhutoryansky8 жыл бұрын
+Seth Connell, I am glad you found my channel, and I am happy to have you as a lifetime subscriber. Thanks.
@busraa_8 ай бұрын
No one told me these logical expressions in school... Thank you.
@EugeneKhutoryansky8 ай бұрын
You are welcome and thanks.
@intuitivepariacademy7 жыл бұрын
can you please help me..? actually I want to make a model with the dot and cross product idea. please help me.
@savemey2jnavi3 жыл бұрын
Man, nice music selection like Rossini's William Tell Overture with a beautiful animation for a math explanation. You got an inmediate new suscriber in myself!
@EugeneKhutoryansky3 жыл бұрын
Glad to have you as a subscriber. Thanks.
@jiaqihuang7762Ай бұрын
Thank you for this video! That makes so much sense!
@EugeneKhutoryanskyАй бұрын
I am glad you liked my video.
@samrat67202 жыл бұрын
This was the most ominous way I've learned about the dot product and cross product
@dougvitagliano75128 жыл бұрын
These videos are awesome! Thanks
@EugeneKhutoryansky8 жыл бұрын
+Doug Vitagliano, I am glad you like them.
@abhishekcherath23238 жыл бұрын
Great work. Thank You.
@EugeneKhutoryansky8 жыл бұрын
Thanks for the compliment.
@1schwererziehbar16 жыл бұрын
This is the good stuff. The right stuff.
@kingkirby89608 жыл бұрын
Physics + Mathematics = One new subscriber.
@EugeneKhutoryansky8 жыл бұрын
+Sausage Biscuit, thanks. I am glad to have you as a subscriber.
@kingkirby89608 жыл бұрын
No, thank you. :)
@tuandunglai24916 жыл бұрын
how length can exactly equal to area?
@technus1025 жыл бұрын
value of length is value of area
@Dragoneer3 жыл бұрын
Equal in magnitudes I'm guessing is what they mean
@lightoftheFather_3 жыл бұрын
Imagine a cardboard attached to the base of the vector. The length of the vector would, therefore represent the area. The length even represents force in Newton, and other things, so the units don't have much to do with it, it's about the magnitude.
@poisenbery Жыл бұрын
these videos are amazing
@EugeneKhutoryansky Жыл бұрын
Thanks for the compliment.
@itz.zaid__44102 жыл бұрын
Mam you are a best teacher in the whole world
@EugeneKhutoryansky2 жыл бұрын
Thanks for the compliment.
@rgokulram99256 жыл бұрын
You videos were awesome like unfolding mathematics in to a movie , it makes looking outside world in terms of math . I thank you so much for your videos ,love from india
@EugeneKhutoryansky6 жыл бұрын
Thanks. I am glad you like my videos.
@jvillalobos69886 жыл бұрын
that final hand move was epic!
@ilijamajcen5426 Жыл бұрын
exactly what I need in only 4 minutes. thanks
@EugeneKhutoryansky Жыл бұрын
Thanks.
@sarikanigar59363 жыл бұрын
0:22 Wait, how could the 'length' of arrow representing the cross product be always equal to the 'area' of the parallelogram ?
@clarelee33973 жыл бұрын
it’s the numerical values are that equal
@azysgaming84102 жыл бұрын
Thanks Clare.
@thestarinthesky_3 жыл бұрын
The best explanation i have ever seen!
@EugeneKhutoryansky3 жыл бұрын
Thanks for the compliment. I am glad you liked my explanation.
@seanwiesen74188 жыл бұрын
Thanks Eugene. This is a very good explanation.
@EugeneKhutoryansky8 жыл бұрын
+Sean Wiesen, thanks for the compliment.
@EigenA2 жыл бұрын
Jeez that music on the RHR got me pumped to go into 16th-century battle
@madch3mist6 жыл бұрын
Nice animation and succinct differentiation between the scalar and cross products.
@joeye65563 жыл бұрын
This was really helpful to visualize, but I'm still confused as to why multiplying 2 vectors results in a third one that forms a 90 degree angle from where the 2 vectors connect. Why does it happen?
@AMANSINGH-tb6pj2 жыл бұрын
This is what has been bugging me since i was introduced to vectors in school. This is my biggest lack of understanding in the fundamentals of physics. I have tried a lot but never found q clear explaination to this. So i have convinced myself that this rule is something that humans have agreed upon by conducting experimentation and finding results that just fit this type of calculation, and no one came up with it on thier own. While the dot product is very obvious and can be understood by doing your own thought experiments.
@desrepeerc2063 жыл бұрын
Excellent video, this is how it should be taught in physics classes
@EugeneKhutoryansky3 жыл бұрын
Thanks. I am glad you liked my video.
@demartlectus11813 жыл бұрын
The music is William Tell Overture (Horse Race song)
@balajid11576 жыл бұрын
Superb presentation and explained in a simple manner.
@EugeneKhutoryansky6 жыл бұрын
Thanks for the compliment.
@conceptscracked82814 жыл бұрын
Explained Well, teacher! However, let me summarize the video for further clarification. CROSS PRODUCT 1) The MAGNITUDE of the vector resulted in cross product is the AREA OF PARALLELOGRAM formed by the two vectors. 2) The DIRECTION of the vector resulted in cross product is always PERPENDICULAR to the original vectors. 3) A*B = -B*A (Reversing the order of the original vectors changes only the direction of the final vector) DOT PRODUCT 1) The MAGNITUDE of the vector resulted in dot product is the PRODUCT of the length of first vector multiplied by the length of PROJECTION of second vector on the first vector. 2) No vector is resulted in dot product; it is always a scalar number. 3) A.B = B.A (Reversing the order of the original vectors do not change the final scalar value)
@The_MatEngineer7 жыл бұрын
when considering the second arrow (segment on dot product) the length of that side of the triangle is simply the x component of the the second arrow vector.
@akashm90526 жыл бұрын
amazing video , amazing work 👌 keep it up👍
@EugeneKhutoryansky6 жыл бұрын
Thanks.
@Anna-qp1fi2 жыл бұрын
Excellent explanation, thank you!
@EugeneKhutoryansky2 жыл бұрын
Thanks. I am glad you liked my explanation.
@elaine38672 жыл бұрын
Thank you so much. It really helped my understanding on the topic
@EugeneKhutoryansky2 жыл бұрын
I am glad my video was helpful. Thanks.
@hairyfiddler22743 жыл бұрын
That helped a lot thanks 🙏🏼
@fightforfitness22566 жыл бұрын
Thanks for your effort .
@UnfilteredCactus6 жыл бұрын
Thank you so much... the language barrier and lack of proper explanation from my physics professor had my whole class confused