Kinematics Part 2: Vertical Motion

[@ProfessorDaveExplains]

You guys! I'm so sorry, I screwed up the equation at 5:30, final velocity should be on the left and initial velocity should be on the right. When written out correctly the arithmetic will work out to the number given, however. Sorry about that!

[@MysticNach]

Professor Dave Explains thank you, I was going crazy for a bit lol

[@masdfghjlwcmr]

That explains why. Whahaha thank you

[@defritzel]

my lord. had my wife and son trying to figure out the math on that one. Thought I was going crazy!!

[@menacereconnaissance7406]

all people made mistakes

[@Renagade01]

ahmmmm im stupid at p6 so im just gonna ask what youre sayying here is that it must be around 65.4 or something in 5:30 ? am i right XD?? haahah ahaha i also tried to calculate......but anyways a really great help

[@theodoresweger4948]

I like that statement," we tend to spend most of our time of earth."

[@arielnwalton2644]

That stood out to me aswell.

[@kasperchristensen8416]

_The ISS crew has entered the chat ..._

[@Occ881]

Is we tend to spend most of our time on the Earth,not of the earth

[@luvochiya4134]

😂😂😂😂😂😂😂😂😂

[@aboobakarmohammed1242]

This video is meant for long time validity it seems lol

[@alexanderl7059]

I'm not even learning this in school right now but I still watch these to learn new things!

[@ProfessorDaveExplains]

that's what i'm hoping many more will do! lead the way!

[@thefisherman9553]

Who the fuck does that

[@demetrius8184]

@@thefisherman9553 so you know all 7 billion people in earth?

[@yohanlingan4854]

Same XD

[@yohanlingan4854]

What grade are ya? Me grade6

[@kellyc2915]

Thanks!

[@purgeziadk1009]

Bro casually donated 10$

[@francisgregoryku1689]

PROFESSOR DAVE MAHH MAYYNN saving me in chem last year and saving me in physics this year

[@sophiaduera-cardozo7941]

me too ;-;

[@dsdespina1]

Same! honestly couldn't have done this without him.

[@aboobakarmohammed1242]

professor at rescue :)

[@cja12345]

bro you are literally so amazing man. Strugglig for the past week on kinematics and now I understand it in less than an hour. Subscribed.

[@tochoXK3]

4:03 An alternative to using the quadratic formula is calculating how far the rock will go up, then calculating how long it will take to fall from this height to -100m. Then, the velocity is 0. (This alternative isn‘t strictly better)

[@BBCxJEAN]

it is.

[@syncradar]

​@@BBCxJEANHow?

[@Firnas_7]

in this way why my time is 4.63 sec while in the video it is 5.65

[@shootandfish2]

@@Firnas_7 Need to add the time rock is in air for the initial upward motion (I got 1.02 sec plus the 4.63 sec =5.65 sec)

[@shariffahpateyahazvi8718]

its a pity i didnt have you during my high school but am greatfull i have you now in university where we still take physics and chemistry for our molecular biology and genetics bachelor degree

[@DANGERBOY-qz8wy]

I'm kinda confused in 2:49 because how did you manage to obtain 4.5s since what I did is (t^2 = 20.4s^2 Don't we just have to square second and time and remove the power so they would be quite equal)??? Since if we didn't square time then it would mean T^2 = 4.5s? which puzzles me.

[@raton324]

you do √20.4 not 20.4*20.4

[@ichione732]

Professor Dave your'e videos are really informative even our science teacher uses your videos as reference in our whole 4th quarter which is about physics I don't even need my module anymore just your'e videos keep up the outstanding work and hoping for more content in the future. greetings from Tagum City! gikan sa pinakagwapo

[@sahilpatel5298]

Literally save so much time and gained more knowledge than a whole month of spending of kinematic at my college. WOWW

[@ianstuder8970]

Napped for a week and missed everything, watched this at 2am the day before the test, and then proceeded to finish first and get a 100. Luv u dave ❤

[@angeliemaebonaobra4448]

Thank you so much professor Dave

[@shootandfish2]

I agree with the comment of avoiding the quadratic eq by solving in 2 parts. I got 5.1 meters up in 1.02 sec, now v initial = 0 and drop is -105.1 m. my answers agreed with yours to the hundredth. Otherwise, excellent video. Currently tutoring college nephew, it's been over 45 yrs since I had University Physics.

[@Paw-Patrol-Lover]

You may be my life saver Professor Dave. Yours may be simple but easy to learn as well. Thanks, hope I do well for my quiz tomorrow. (Also the Horizontal Motion is part) I understand the simple mistake on 5:30, but hey mistakes happens. And the answer was still the same when I calculated it. Thanks.

[@Paw-Patrol-Lover]

Also at the checking comprehension, can the answer be -321.5 meters, because when I calculated, the result I had was about -321.489 meters, so I just rounded off to the nearest tenths.

[@jerasong2196]

Hi Dale.

[@clumsyhes2103]

3:42 watch your head, bud! that rock is going to hit you! you won't be able to study physics anymore if you get bonked on the head with that rock! oh nooo! :o

[@mem8190]

Excuse me Professor Dave, at 5:43 I got a different answer which is -65.4 because I transferred the 10 to the other side, could you please explain how you got your answer for more clarification? thank you so much 💙.

[@fizsing2615]

yea i got the same answer, i cant understand why it is that way

[@vigzz9569]

Dude please same why did he flip equation!!!

[@xodusgraphicdesigns3384]

He wrote the wrong equation . On screen it said : Initial Velocity = Final Velocity + Acceleration x Time. However it should have said Final Velocity = Initial Velocity + Acceleration x Time. Use that and you will get the same answer as him.

[@JuanGabrielLuna-zd9pn]

He did not wrote the equation wrong. The answer is simply wrong. He used Vi=Vf+at to find Vf. Use algebra.

[@Firnas_7]

the cliff is -321.489 m tall🗿 (since it is a cliff the length can not be negative number so that is why it becomes 321.489)

[@GK-TECH24]

Dear Pr. I have one question for u ... here is my question:- When a ball is thrown from a top of building upward and reached the ground why the decent velocity isn't negative and why the time in the first case where the ball reach the thrown point isn't considered ?

[@ranjeetsohanpal752]

I like that you put a comprehension question in the end which helps us to revise the topic we have just learnt from you,Love you Dave,Stay Awesome.😊

[@xx_baav2]

i have a question in 2:51 did you just divide it to get the value of t?

[@tommijones8095]

When you changed the variables from the original ones it completely confused me.

[@grimreaper3607]

5:03 i cant understand at this point...how can u know where to assign the numbers

[@angelfayebaculi4496]

Hi sir, how did you get the 4.5 s at 2:48, I still can't figure it out how you got it

[@ProfessorDaveExplains]

if you are having trouble with basic algebra, you will have to go to my algebra playlist and review the fundamentals. this series assumes basic ability in algebra.

[@ionloghin2172]

Once again you have saved my future, thanks for making this look easy because it really is.

[@realityisenough]

I think the formula at 5:36 should be Vf=Vi+at not Vi=Vf+at? Maybe I'm wrong?

[@ProfessorDaveExplains]

oh no! what a stupid mistake :( thanks for catching that!

[@realityisenough]

Hey it made me look into it in more depth so it's drilled into my head now haha :p You can probably just shove an annotation box over it

[@CarbonsHDTuts]

So would the answer be -44.88m/s instead? Please if you could reply that would help alot, just to make sure I actually understand!

[@aresemasahilu2411]

you are the cause to love physics thanks

[@Decco6306]

This is why i love physics its makes your mathematics classes that seem useless and applies them to the real world, to make it feel like all this effort means something, I think that mathematics and physics should be taught as the same class so that the students have an appreciation for the use case of mathematics. Most students that i know never took physics and only Math, and now hate math because the average person is not creative enough to apply mathematics to the real world. That would mean they would have to make these discoveries themselves, that took geniuses to do.

[@hareecionelson5875]

I remember the first time I realised by myself that the equation for time is just a quadratic formula, I was so excited. Really helped in exams being able to write "s=ut + 1/2at^2, so use quadratic formula with t = etc etc" other people would solve for v first and then use v=u+at because it's simpler, but leaves more room for making mistakes and rounding errors

[@AngelTaylorgang809]

I saw professor dave whipping a model x performance not too long ago in san Diego. I'm glad he's doing good. He deserves it

[@ProfessorDaveExplains]

I don't know what this means.

[@artzmasterz5647]

@@ProfessorDaveExplains he saw you driving a testla in san diego

[@ProfessorDaveExplains]

@@artzmasterz5647 Well that didn't happen so it must be a doppelganger.

[@fowotaku821]

For the equation at 1:46, should there not be a initial position at the right hand side of the equation?

[@kathleenilagan4636]

Hi! Help me understand how did you get the 4.5 from the -100 and -4.9

[@ProfessorDaveExplains]

don't forget to take the square root!

[@kugaththeplaguefather6332]

2:51 how time=4.5? sorry if this is a dumb question im quite new to physics

[@carultch]

The equation reduces to d = 1/2*a*t^2, since the initial velocity and initial position were zero. Given d = 100 m, a = 9.8 m/s^2 and the 1/2 factor, put them all together, and rearrange so t is the subject of the equation and get: t = sqrt(2*d/a) Plug in the data: t = sqrt(2*100/9.8)

[@mariiict2255]

Thank you very much! This made it a lot easier to understand 😄.

[@rorysnow7937]

5:40 I did the same problem following all the steps and I instead got 65.4 m/s for Vf instead of -45.4. Have I done something wrong?

[@BoZhaoengineering]

Professor, if we use postion vector where origin at the man throwing the stone and pointing to the rock, during the process, the position vector is zero when rock travel back to which the man sits and going further down to ground. The position vector finally becomes - 100 m .

[@Phoenixsquad77]

How was the quadratic equation applied in the first equation 5:36

[@arzalalbuchari7095]

that feeling of dread when you instantly realize you forgot how to multiply decimals

[@syub2407]

@ 3:10 cant we use v(final)^2 = v(initial)^2+ 2gd but my answer is 44.27. Which is given by V^2= 0^2 +(2*-9.8*-100)

[@TheAce736]

"But with vertical motion, down will always be negative.” sobs in gdscript

[@TechWizeGuy]

Your videos are just awesome

[@angelicarosales5979]

Thank you for the information Professor Dave! Very helpful in my science class.

[@elaizahjeanbatiancila9911]

Professor Dave can you show me the whole solution on how did you get the time on the vertical solution when the initial velocity has a value and how you get the unit?? please

[@ProfessorDaveExplains]

the one with the quadratic equation? check out my mathematics tutorial on that subject if it's confusing!

[@elaizahjeanbatiancila9911]

Okay thank you Professor Dave..

[@elaizahjeanbatiancila9911]

Professor Dave i have a question why does the unit disapper??

[@ib-physics-exams]

Thank you for all your beneficial high quality videos. I often mirror many of your physics videos in most of my lessons to my students .

[@alezaen7609]

Gravitational acceleration for objects moving downwards is +9.8m/s2 not -9.8m/S2 this value is for objects moving upwards

[@ProfessorDaveExplains]

The value of g is always negative. It does not change according to the motion of an object. Objects moving downward are moving in the negative direction.

[@alezaen7609]

No sir gravitational acceleration for objects moving upwards is -9.8ms-2 because it is moving against the gravity

[@ProfessorDaveExplains]

Again, it’s always negative.

[@alezaen7609]

Why the gravitational acceleration for objects moving downwards is -9.8m/S2 please justify it sir

[@alezaen7609]

Other KZbin site's including my sir are saying that the value of g for objects moving downwards is approximately 10m/S2 while for objects moving upwards is approximately -10m/s2

[@csanilkumar5415]

Professor you are wrong GM ÷ r^2 = total displacement ÷ total time taken ^2 Or g = d ÷ t^2 Answer for your question GM ÷ r^2 = 642 .978m ÷ 8.1sec^2 Therefore , height of the cliff = 642.978m.

[@AmanSingh-db3nr]

Sir I am a big fan of you ,your way of teaching is awesome and so simple that one can easily understand everything😊😊👌👍

[@marlongrau246]

I think we need to add the time of object thrown upward and the time of object when fallen to the ground.

[@ProfessorDaveExplains]

It's all done in one calculation. There is only one force acting upon the object.

[@crazyboyz6065]

5:43 Isn’t it v= u + at?

[@nathalieperez8039]

for the second the final velocity should be 65.37 because we had to add it over to the other side. right?

[@ProfessorDaveExplains]

oh no, i think i put vf and vi in the wrong spots! the number in the answer is correct, but i seem to have screwed up the equation :(

[@zigtim]

Thank you! I was driving myself crazy over this.

[@역행호흡의역행]

Do you know v = root(2gh) and T = root(2h/g). If the ball(?) starts at v=0 at the vertical movement. And which age do they learn those things at high school? In korea at 16 years old.

[@shravyakuchipudi4072]

I learned it when i was 12 I am from India

[@missjolly5860]

I got a question sir, in 5:35 we need to multiply the -9.8 m/s to 5.65 s right? my answer is -55.37 and then divided by both sides to cancel it so final velocity is equals to 10 m/s divided by -55.37, why is my computations wrong? 😭

[@kbikiro9728]

It looks like mr dave accidentally reversed the equation the correct equation is Vf = Vi + at, if we hypothetically used the incorrect equation Vi = Vf + at, we would add 55 to the both side so we can get 65.37 m/s 10 = x - 55 10 + 55 = x - 55 + 55 x= 65

[@kavita3689]

sir i am really impressed by your videos.these are really helpful

[@nathanielruambil2124]

Please can you explain where did you got that 0.5 in question 1 at 2:34..please

[@carultch]

It means the same thing as 1/2. It comes straight from the equation. If you are wondering why it exists in the equation, it comes from Calculus. Integrate a constant acceleration relative to time twice, and you get a leading factor of 1/2, and a squaring of the time. A visual interpretation of why this is, is when you graph constant acceleration on a velocity vs time plot, for an object accelerating from rest at a constant rate. The area under the curve is a triangle of height a*t, the base is t, and the area (i.e. the distance associated with this motion) is 1/2*(a*t)*t, or 1/2*a*t^2.

[@CJAzuraPaulin]

Thanks great video😊..but How to find its highest point and time at the highest point?

[@jessabelarca4060]

On 2:48 how did the t become 4.5s?

[@Fartpoopsigma]

Lock in

[@crisdarren7308]

im stucked in 2:42. how'd you get the 4.5s?

[@raton324]

wtf, are you dumb or are you joking? 100/4.9=20.4, √20.4=4.5

[@kaiibleu7004]

at 5:20 I understand where -3.6s came from but im not sure how you converted it to 5.65s and would using -3.6s be wrong if I plug it the equation although its negative

[@abdistic1047]

Where did the -3.6s come from?

[@bahandiannefaithg.2230]

2:49 i didn't know how'd you get the 4.5 seconds. 😩😩 can anyone please help me??

[@tanviakhtar1527]

same here lol

[@17.vx0]

Shouldn't the acceleration be positive when thrown downwards and negative when thrown upwards since it goes against the direction of gravity? Would someone please explain?

[@ProfessorDaveExplains]

Acceleration is constant since gravity is constant

[@jaronrallos3844]

Hey Professor Dave, isn't upward motion for gravity -9.8m/s while downward motion is +9.8m/s? I'm very confused.

[@ProfessorDaveExplains]

Acceleration due to gravity is independent of the motion of any object, it's always negative because gravity always pulls things down to the ground.

[@mahederalemu3756]

Where is the time which take up ward ? We should solve it in the formula of vf=vi +at

[@jsam2787]

Nice work Sir

[@cryztalresulta5851]

sorry but i cant get how how -4.9x² + 10.0x + 100 becomes 5.65 the answer

[@leahgroh5610]

quadratic formula

[@ellenmonay3273]

With the quadratic formula my answers were reversed my positive was 3.6 seconds and my negative was -5.65. I am also confused

[@myrrhagoyokpin8057]

for the first problem, why did we not take into account the initial position of the rock?

[@Tekato-]

@0:17 position and velocity are misplaced. pls correct me If I'm wrong.

[@ProfessorDaveExplains]

i'm just listing words, there is no specific order

[@seemakulkarni2622]

Fantastic! Am very thankful to my sister for suggesting me to see this video 😊

[@carloschisenga.7794]

Is there any other way of solving that without using the quadratic formula?

[@rashidfaheem9838]

Need an explanation about, is 'g' is negative or positive when object is fallen on the ground?

[@ProfessorDaveExplains]

g is always negative by convention

[@leenss536]

PROFESSOR DAVE I LOVE YOUU😫

[@beatriceabadilla]

hi prof dave! love your videos!! how will I know which equation to use? why can't I use vf=vi+at for both the questions in 3:06?

[@ProfessorDaveExplains]

so for the first one we don't know how long it is in the air so we don't have t, and that leaves two unknowns, so we have to use the one shown. for the second one now we have all the variables so we can use that equation.

[@beatriceabadilla]

@@ProfessorDaveExplains ohhh okay I get it so we use the vt=vi+0.5at when we want to know the position of the object then plug in t in vt=vi+at... thank you for being responsive prof dave!! more power to your channel hihi

[@SabrinaXe]

For the 2nd question, shouldn't initial velocity be -10 and not +10?

[@SabrinaXe]

Nvm...

[@saatvinagarajan3302]

Can we use this videos for a levels?

[@GAREZSOBALWANT]

on 2:48 why I get is 20.40?

[@Firnas_7]

there was t² in the right side then -100/-4.9 would be 20.40 but you have to root it because there is t² . you need the value of 't'. not t². hope this helps

[@allie7015]

Is the addition of 100 to both sides to standardized the equation is constant? or does the value depends on what is on the left side?

[@ajaxx_x]

I dont get it. The time that did you use in vf was it the negative answer in quadratic?

[@shreyass7734]

i realy luv all of your videos i have a doubt the rock falling from the height of 100m how is it irrespective of the mass ?

[@carultch]

Because both weight and inertia are proportional to mass, and come as a package deal. Mass cancels out of the equation, and acceleration in free fall only depends on the environment where it happens (i.e. the properties of the planet).

[@shimeliswansara3177]

How can we solve horizontal velocity when an object fall vertically

[@davidjoshvillegas9592]

Professor, i got confuse in 2:48 on your video. The equation was (-100m)/4.9m/s^2)=t^2 How come the quotient is 4.5??? When i use the calculator, it wasnt 4.5 but it was 20.408. Reply asap. I think you got it wrong professor in dividing 100 and 4.9😑

[@ProfessorDaveExplains]

don't forget to take the square root

[@AyaMohamed-ij6hu]

you are a lifesaver. Thank you

[@marlongrau246]

I'm just curious. I'm confuse with the question how long is in the object in the air when it was thrown upward at a height of 100m. Is the height from 100m when the object is thrown upward doesn't have to be related when the object is falling down? The total time is the same?

[@ProfessorDaveExplains]

It's displacement, so it takes into account the direction of displacement and the direction of motion. Velocity is positive but acceleration is negative, so the math works out fine.

[@ninj6643]

Professor Dave im having trouble with calculating this question our professor is extremly bad at explaining please help If Jacks egg hits his friend Mark in the head,What is the speed which it hits his head? His friend Mark is 1.70m tall

[@ProfessorDaveExplains]

Right, so there is nowhere near enough information to answer that question. In fact there is literally zero useful information for answering that question! His height is irrelevant, after all.

[@ninj6643]

Professor Dave Explains thanks professor

[@renanpongilio7062]

why for formula Vf = Vi +2ad is sometimes Vf2 = Vi2 +2ad?? Great channel by the way

[@carultch]

It's squared for both equations. The first copy of that equation is incorrect.

[@mnrblz8340]

If you throw the rock directly down rather than dropping it, and you are required to solve for the initial velocity, how would you solve for it given the time and distance only?

[@carultch]

d = 1/2*a*t^2 + v0*t + d0 define d0 = 0, as the the object starts at the origin of our coordinate system define the positive direction as downward. Given t and d, and given that this is a free fall situation where a=9.8 m/s^2, our unknown is v0. Solve for v0 d = 1/2*a*t^2 + v0*t d - 1/2*a*t^2 = v0*t v0 = (d - 1/2*a*t^2)/t Plug in a, the known t, and the known d, and you will find v0.

[@mnrblz8340]

@@carultch Thank you :)

[@TitserEnzymeTV]

Prof dave, can I ask because the original in your horizontal motion video , the formula is dt = d0 + vi t + 1/2 at2 . WHy in the vertical, it seems d0 is not included?

[@carultch]

It just means that the initial position is defined where d = 0

[@yosefrabinow9788]

thanks this video really helped me

[@ifebunachiagu7607]

Good afternoon Professor Dave,, I have been following your channel. Please I don't know where you the 0.5 please can you explain

[@ProfessorDaveExplains]

it's just 1/2

[@DelightChidiebere]

How do you know which equation to use? 😢

[@maverickvillanueva9667]

My prof told me "If the object goes upward, the acceleration due to gravity is negative then Positive if downward" because gravitational pulls downward with the acceleration of constant (9.81m/s).

[@ProfessorDaveExplains]

Acceleration due to gravity is always negative. It pulls in the negative direction.

[@helmetongrass1893]

"SCP 5094 is not real" professor dave: hold my beer

[@juanpedraw4245]

Hey, guys, here's another way to find the answer to height. h=1/2(g)(t^2) h=(1/2)(9.81)(t^2) The gravity should ALWAYS be positive though.. It still works!

[@obligatoryfail9550]

That's the same equation he used, just without the initial velocity.

[@annabethbardon4295]

Nah. It's negative.

[@gshsenpai6446]

Bro if it were positive, people would been projectiled into space by now Acceleration is a vector, due to it always pointing to center of the earth. Thus a = -9.81m/s^2

[@Yskaaaaa]

how did you get the 4.9v²

[@noahshemelis1902]

isn't acceleration due to gravity negative for a body moving upwards and positive when moving downwards?

[@ProfessorDaveExplains]

It's always negative, always downward.

[@gix9816]

@ProfessorDaveExplains, If gravity is a force, why is it included in kinematics?

[@carultch]

Because it is a "coincidence" that the force of gravity per unit mass on all objects on this planet is approximately the same everywhere on this surface. Such that when gravity is the only force, all objects accelerate at the same rate when in free fall or projectile motion. I put the word "coincidence" in quotes, because there is a lot more to it than just a coincidence, and you learn it eventually when you study general relativity, why it is the case that gravitational mass and inertial mass are a package deal.

[@asnairahbaraotong6208]

Hello Professor Dave. Do you have an explanation about 3-dimensional motion?

[@安娜迪]

may i ask where'd you got the 0.5 in 2:02?

[@ProfessorDaveExplains]

1/2

[@arpitarora8600]

thank u so much prof, for such a brief explanation. i

[@hildyb676]

This is awesome! I love your clear explanations, but i'm having trouble getting the 2 numbers you got when you put you a,b and c values in the quadratic equation. I keep trying, and plugging them into my calculator but it keeps saying error. Do I need a specific sort of program installed in my calculator for quadratic equations or is it just and error i'm making while plugging in my numbers? Thanks!

[@ProfessorDaveExplains]

it can be pretty easy to make arithmetic errors! maybe simplify on paper step by step, watch your signs and order of operations. i have a tutorial on the quadratic formula in my math playlist if you need practice!

[@hildyb676]

Alright, I'll do that! Thank you so much for the quick reply, I have a test today!

[@kennedyandjory]

Im having the same issue, did you ever figure it out? Haha

[@MichaelJones-ek3vx]

Relearning physics and math at seventy-five 3:44 creates order internally. After the election, I need that.

[@privateservers2damax]

Wow! How is it sir, have you been making nice progress?

[@Raeyenn]

how did you get 4.5s on the first problem, sir?

[@betelihembefirdu5865]

First i would like to say thank u for ur best explanation but i have one question since the rock is dropped down ward acceleration due to gravity must be positive not negative right?

[@ProfessorDaveExplains]

Down is the negative direction by convention.

[@betelihembefirdu5865]

Okay thank u😊