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Zak's Lab
США
Добавлен 17 авг 2020
Physics and Math with an emphasis on WHY.
Zak's Lab is primarily a physics and calculus instruction channel with hundreds of short lecture and example videos currently covering:
Physics I and II (trig-based). This crosses over to AP physics.
Physics I (calculus based).
Physics II (calculus based) is in progress.
Calculus I is coming Spring '24.
Calculus II
Browse dozens of playlists organized into the corresponding college course category. To see the full collection of playlists, please click the "playlists" button, as they do not all appear on the cover page.
I also like making math animations and algorithmic art, and those each have their own playlists as well.
Zak's Lab is primarily a physics and calculus instruction channel with hundreds of short lecture and example videos currently covering:
Physics I and II (trig-based). This crosses over to AP physics.
Physics I (calculus based).
Physics II (calculus based) is in progress.
Calculus I is coming Spring '24.
Calculus II
Browse dozens of playlists organized into the corresponding college course category. To see the full collection of playlists, please click the "playlists" button, as they do not all appear on the cover page.
I also like making math animations and algorithmic art, and those each have their own playlists as well.
Moment of inertia for a cylinder with increasing density (moment of inertia integral).
Given a cylinder of mass M, radius R, length L and quadratically increasing density rho=ks^2, where s is the distance from the symmetry axis, we calculate the moment of inertia of a cylinder about its symmetry axis.
We begin with a reminder of the formula for the moment of inertia of a thin shell: I=MR^2, because we plan to split our cylinder into nested thin cylindrical shells.
Next, we get a reminder of the definition of density: rho=M/V, which can be turned around to say M=rho*V, but only if rho has a single well defined value over an entire volume.
This is part of the motivation for splitting into thin cylindrical shells: using a thin shell mass increment of dm, the entire volume of the...
We begin with a reminder of the formula for the moment of inertia of a thin shell: I=MR^2, because we plan to split our cylinder into nested thin cylindrical shells.
Next, we get a reminder of the definition of density: rho=M/V, which can be turned around to say M=rho*V, but only if rho has a single well defined value over an entire volume.
This is part of the motivation for splitting into thin cylindrical shells: using a thin shell mass increment of dm, the entire volume of the...
Просмотров: 61
Видео
Acceleration and force on the driver as a car brakes to a stop.
Просмотров 992 часа назад
Given the initial velocity of a car and the braking distance, we calculate the acceleration of the car, then - given the mass of the driver - we compute the horizontal force on the driver as a car brakes to a stop. Special note at the end: verification that kg*m/s^2 are Newtons (units of force).
Free fall in an accelerating elevator: relative velocity at impact.
Просмотров 904 часа назад
If you are in an elevator accelerating downward, how long will it take for a ball to land on the floor, and what's the relative velocity when the ball strikes the floor? We analyze this problem from two different perspectives. First, we use a stationary "external" reference frame, in which the elevator is accelerating at 3.5m/s^2, and we solve the problem using the standard kinematics equations...
Vertical free fall with two objects + accelerating reference frame analysis.
Просмотров 344 часа назад
In this vertical free fall problem, we are given two objects in free-fall. One ball is dropped from the top of a building, and the second ball is thrown straight upward. We solve for the time at which the balls collide, the height at which the balls collide and the relative velocity of the balls when they collide. We notice a coincidence that's too important to ignore: the relative velocity at ...
How to find the final velocity and displacement for constant acceleration from rest.
Просмотров 517 часов назад
Given a car starting from rest with a given acceleration and the time duration for that acceleration, we find the final velocity and displacement by using the constant acceleration kinematics equations.
Derivation of the integral of 1/(a^2+x^2)=1/a*arctan(x/a)+C.
Просмотров 21916 часов назад
You've probably seen the integral of 1/(a^2 x^2) in a standard table of integrals, but how do we derive it? It turns out we can use a simple u-substitution or informally use the reverse chain rule in order to compute the integral of 1/(a^2 x^2). In this video, we start by showing the chain rule backwards approach to the integral, then we use a u-substitution to verify that we get the same answe...
Find the definite integral of x*sqrt(x-1) on [1,2]: u-substitution and transforming the limits.
Просмотров 48419 часов назад
We use a u-substitution and transform the limits of integration to find the definite integral of x*sqrt(x-1) on the interval [1,2]. The standard thing we try first for an integral of this type is to let u equal the interior of the square root. So, we let u=x-1 and du=dx, but we have to take care of the x in the integrand. This is where we solve for x in our original substitution to get x=u 1, a...
How to find the arc length of a semicircle using calculus.
Просмотров 69219 часов назад
We find the arc length of a circle of radius 1 by using the standard formula for arc length in rectangular coordinates. Bonus: one minute derivation of the arc length formula as a reminder! To compute the arc length of a semicircle, we need a formula for the semicircle as a function, so starting with the formula x^2 y^2=1 for a circle of radius 1 centered at the origin, we solve for y and get y...
Moment of inertia with variable density: thick spherical shell with variable density rho=k/r.
Просмотров 12121 час назад
Given a thick spherical shell of mass M, inner radius a, outer radius b, and non-uniform density rho=k/r, we compute the moment of inertia in terms of M, a and b by using our previous result for the moment of inertia of a thin spherical shell: I=1/3MR^2. We start with a quick reminder of density: rho=M/V which can be turned around to say M=rho*V, in other words, we can find mass by taking densi...
Cut the parabola in half using calculus: y=1-x^2 cut in half by a horizontal line y=c.
Просмотров 318День назад
In this challenging area integral problem, we are given the region bounded by y=1-x^2 and the x axis. The goal of the problem is to calculate c so the line y=c cuts this area in half, and we cut the parabola in half using calculus. We begin by computing the total area under the parabola y=1-x^2, and this is just a standard definite integral on [-1,1] of 1-x^2. We take advantage of symmetry and ...
Tension before and after a mass and pulley system is released (Atwood machine problem)
Просмотров 22214 дней назад
Given a mass and pulley system on a smooth incline, we compute the tension in the string joining the masses when the system is held stationary, then we compute the tension in the Atwood machine when it is accelerating. The analysis of the stationary mass and pulley system is simple: the tension in the string must be equal to the weight of the hanging mass in order to guarantee the hanging mass ...
How to find the impact velocity of a projectile launched from a given height.
Просмотров 37514 дней назад
Given a projectile launched from a given height with a given speed and launch angle, we show how to find the impact velocity of a projectile. We begin by breaking the initial velocity into components using sines and cosines in the usual way, and we note that the final x component of velocity (the x component of the impact velocity) is equal to the initial x component of the velocity, so that pa...
How to find the volume of a paraboloid using shells (y=1-x^2 revolved about the y-axis).
Просмотров 15114 дней назад
A paraboloid of revolution is defined by the curve y=1-x^2, which makes a region in the first quadrant bounded by the x and y axes. Revolving this region about the y-axis, we obtain a solid paraboloid, and we show how to find the volume of a paraboloid using shells. We start by visualizing a thin cylindrical shell with an arbitrary radius of x. This shell has a height given by the height on the...
Integral of sin2x/(1+cos2x) on [0,pi/4] using the reverse chain rule or chain rule backwards.
Просмотров 34514 дней назад
Whenever we see the derivative of the denominator in the numerator, we know it integrates to the natural log of the denominator! In this video, we compute the integral of sin(2x)/(1 cos(2x)) using the chain rule backwards, also called the reverse chain rule. In other words, we're recognizing the consequences of the chain rule in an integral, rather than relying on an explicit u-substitution. We...
How to transform the limits of integration: definite integral of 3x/sqrt(x^2+1) on [0,2].
Просмотров 14314 дней назад
We use a u-substitution to compute the definite integral of 3x/sqrt(x^2 1) on the interval [0,2]. Let u=x^2 1, du=2xdx, and we show how to transform the limits of integration in terms of u, so the entire integral is transformed to u-space.
Integral of (2x+5)^7 using the chain rule backwards vs. formal u-substitution approach.
Просмотров 43014 дней назад
Integral of (2x 5)^7 using the chain rule backwards vs. formal u-substitution approach.
Trig substitution with completing the square: integral of 1/(x^2-4x) using a secant substitution.
Просмотров 21321 день назад
Trig substitution with completing the square: integral of 1/(x^2-4x) using a secant substitution.
Pulling a block up an incline with force at an angle: find normal force and acceleration.
Просмотров 32621 день назад
Pulling a block up an incline with force at an angle: find normal force and acceleration.
Find the speed of a particle on a spiral trajectory given the position vector (2D kinematics)
Просмотров 15721 день назад
Find the speed of a particle on a spiral trajectory given the position vector (2D kinematics)
How long will the projectile stay above a given height?
Просмотров 59821 день назад
How long will the projectile stay above a given height?
Moment of inertia of a ball with non-uniform density (linearly increasing density rho=kr).
Просмотров 9828 дней назад
Moment of inertia of a ball with non-uniform density (linearly increasing density rho=kr).
Thin rod with non-uniform density moment of inertia integral.
Просмотров 6628 дней назад
Thin rod with non-uniform density moment of inertia integral.
How to calculate the moment of inertia of a right triangular slab: another method!
Просмотров 12728 дней назад
How to calculate the moment of inertia of a right triangular slab: another method!
Calculate the moment of inertia of a right triangle by using thin rods (part 1)
Просмотров 144Месяц назад
Calculate the moment of inertia of a right triangle by using thin rods (part 1)
Non-constant acceleration find the equations of motion when a=2-0.1t.
Просмотров 140Месяц назад
Non-constant acceleration find the equations of motion when a=2-0.1t.
Find the net force from lift, drag and weight vectors on a golf ball.
Просмотров 183Месяц назад
Find the net force from lift, drag and weight vectors on a golf ball.
Free fall problem given final velocity, find the time and distance using down as positive!
Просмотров 68Месяц назад
Free fall problem given final velocity, find the time and distance using down as positive!
Using a pendulum to measure gravity (including propagation of errors).
Просмотров 399Месяц назад
Using a pendulum to measure gravity (including propagation of errors).
Integrate a periodic function using symmetry: definite integral of sin(pi*x)cos(pi*x) on [-1,1].
Просмотров 65Месяц назад
Integrate a periodic function using symmetry: definite integral of sin(pi*x)cos(pi*x) on [-1,1].
Integral of cosine using symmetry: definite integral of 2cos(pi*x).
Просмотров 31Месяц назад
Integral of cosine using symmetry: definite integral of 2cos(pi*x).
Two other approaches (both already exploiting the vertical symmetry so the whole area is just the right half of 2/3): First: compute the bottom half of the area by decomposing into a rectangle of sides c and sqrt(1-c) added to the area under the curve (to the x-axis) between x = c and x = 1. So that's c*sqrt(1-c) + ∫(1-x^2)dx between c and 1. Equate that to 1/3, solve for c. Second: work in terms of strips from the curve to y-axis. So ∫xdy between y = c to y = 1, change variable, ∫xd(1-x^2) = ∫x(-2x)dx = ∫-2x^2dx between x =sqrt(1-c) to x = 0. Again, equate to 1/3, solve for c.
Can you plz explain the topic of banking of road? my physics textbook has this topic that gives you a safe turning speed at a sprcific bank angle ,{related to application of centripetal force } its really confusing and there is no video on yt that could help me
What i do intuitively is that when you have integrate f(x) w.r.t x , we have the formula , but we can't integrate f(2x) w.r.t x , so we scale the dx by a factor of 2 and divide by 2 . Now integral of f(2x) w.r.t to 2x is possible.
The second part is a new trick for me 👍
haha, it was kind of a surprise for me when I solved the problem, then after seeing that relative velocity result I realized I should have seen it coming from the beginning. If the accelerations of two objects are the same, then their relative velocity never changes! I formalized it with the accelerating origin idea, but the intuitive idea is clear on its own. z
Very good example! Thank you ❤❤❤
thanks! z
What would you do here if you were given the maximum velocity (at angle 0) and needed to find the tension in general as a function of the angle? Also, if you tried to do this without involving conservation of energy, what would that look like?
hey is the link up for that uncertainty item you said you'd link to? This helps a ton!!
good catch -- I just added the link to the video at the moment where I mentioned it! here as well: ruclips.net/video/UqXy_1rIA1g/видео.html
@@ZaksLab Thank you! I am trying to help someone do this problem and the numbers they got for "g" given their length and average period was 16. They were given what I think is a very different formula from the TA to figure out delta g.
Babe wake up zaks lab new upload
Great videos! I learn so much
awesome! z
@@ZaksLab Do you have any book recommendations for self learning classical mechanics in physics? I'm okay at math but really struggle with physics
This is a great way to show the methods of calc II, but it is not actually a proof, since the values of sine (which are used in the end when you plug the 1 and 0 to the inverse sine function) depend on the fact that π is the ratio between the circumference and the diameter in the first place, so it is kind off circular reasoning. Great content to someone who is studying calculus nonetheless.
this is brilliant, this should have way more views,,, beautifully explained
thanks! z
This is pretty damn interesting.......
What justifies the implicit assumption that the speed is the same in each of the two exit pipes?
the symmetry of the problem - how could one of them be faster if the pipes are identical? Put another way, the entire apparatus is identical if you flip it over the x axis, so everything must be happening the same in the upper and lower half. z
@@ZaksLab There is then an extra assumption that, e.g., the pressures at the end of either pipes are identical, that they have the same length. Moreover, we cannot extend the presented method when the diameters are different. There, we need an extra assumption, like the pressures at the end of each pipe is identical, and to use something like Hagen-Poiseuille equation.
Love form india
so it's the same concept even if it's double angle
lm already here ,and that's a 👌🏽 from me
u made it years ago , buy it helped a soul today appreciate u man
Bonus: I accidentally made another one last month! Better production value, same basic content: ruclips.net/video/uWRezRe-fhU/видео.html
Sir, I was wondering if you could recommend the software you use for writing, recording, and video editing? Your insight would be greatly helpful.
OBS studio to screen capture Powerpoint slides, MathType for equations, graphics in Powerpoint mostly, but Python for most graphs and occasional fancy 3D shapes, edited in Adobe Premiere Pro. z
Great video and explanations. Thank you.
Thanks for the kind words! z
yo fire video
thanks! z
Thx sir, love from india.... I came here after your 3 years old video of spring mass problem thx for that too it helped a lot and you also got many informational videos of my interest:) I would come here again after 2 day to get info about some problems on magnetic field from your channel :)
Thanks -- I spent the summer updating my "sources of magnetic field" content, so you've got a full run of biot-savart aw and ampere's law stuff, if that's the level you're studying. New video production quality is way better too. z
@@ZaksLab yes yes that's the level i have in my syllabus thank a lot
Brainrot I
You can also take u^2 = x^2 + 1, then udu = xdx, so you get 3udu/sqrt(u^2) and if you change boundaries appropriately 0 -> 1, 2 -> sqrt 5, the integrand simplifies to 3du, so the solution is 3(sqrt 5 - 1).
Thankss, its really helpful :)
those who struggle you can just simplify the equation with trigonometry. cos(2x) = 2cos^2(x) -1 sin(2x) = 2sin(x)cos(x) so you get: 2sin(x)cos(x) 2sin(x)cos(x) sin(x) ------------------------- = --------------------------- = ------------ = tan(x) 1+ 2cos^2(x) -1 2*cos(x)*cos(x) cos(x) the integral of tan(x) is: -ln(abs(cos(x)) -ln(cos(pi/4)) + ln(cos(0)) = -ln(sqrt(2)/2) + ln(1) = ln((sqrt(2)/2))^(-1)) =ln(2/sqrt(2)) = ln(sqrt(2)) = (ln(2))/2
What about the diameter of the valve opening?
as long as that's small compared to the vessel diameter, we can make the approximation of zero velocity at the top surface. Of course, the diameter matters a lot if we're taking viscosity into account, but we're treating the fluid as frictionless here. z
@@ZaksLab Thank you
To add, inverse cotangent could have been used, which would not have necessitated the flipping of the bounds of integration but as I've realized, just made intuiting the answer more difficult😢
To add, inverse cotangent could have been used, which would not have necessitated the flipping of the bounds of integration but as I've realized, just made intuiting the answer more difficult😢
Greetings, nice short. I use Maxima a lot.
I'm finally in the process of converting everything I do to Python -- quite a traumatic conversion. I'm glad people are still out there using maxima though! z
Cool man, Nice explanation
thanks! z
Sooo its A(d/dx 1+cos2x) +B= sin2x .....am i right
Good video! good explanation, that cleared up some inconsistencies for me.
thanks! z
Nice work.
thank you! z
Why doesn't the first one work?,please explain
I think the explanation in the video was pretty complete on this -- if you're talking about the first approach to the first method, where sqrt(sin^2(t)) is incorrectly reduced to sin(t), the issue is that the simplification of the square root of the square of a thing should be the absolute value of that thing. By naively replacing sqrt(sin^2(t)) with sin(t), we accidentally convert from a function that is always non-negative to a function that takes on some negative values. So we simplify it to the absolute value of sin(t) in the numerator instead, and that's sin(t) when sin(t) is positive and -sin(t) when sin(t) is negative, and we proceed from there. z
thank you so much!
you're welcome! z
❤
Super awesome!👍
thanks! z
Investigation Jags Ch Unfinished. Copenhagen. V? (32 49.36 40.40 411.44 42.48,😍)
Neat stuff!
thanks! z
Given I have a number of measurements x1,x2,…,xn, I get that to get the uncertainty of the mean related to these uncertainties I’ll have to calculate the uncertainty of the sum, and then divide by n, i.e. sqrt(deltax1^2, deltax2^2,…deltaxn^2)/n. However I am interested in the entire uncertainty of the mean, including the statistical uncertainty (i.e. standard deviation/sqrt(n)) and not just the measurement uncertainty. My understanding is that here I need to again apply the sum formula to add them both together, i.e. sqrt((standard error of mean)^2+(propagated measurement error of mean)^2), am I getting this correctly?
how would this work as a definite integral? I can only find this kind of problem as indefinite
Hey, your question inspired me to put a definite integral of this type on the calculus exam I just finished grading. Here's the video (I include transforming the limits of integration to u-space): ruclips.net/video/sQxC_Cmr6kM/видео.html
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That was explained so beautifully, great visualization! Good job!
thanks! z
He just showed how to derived those formulas. Good if you're getting your masters but its too complicated for students. Just memorize those formulas and you're good to go.
my students can and do learn these derivations in my second semester calculus-based physics (i.e., lower division physics for engineers). If I brought up these circuits in my trigonometry-based physics (i.e., lower division physics for life science majors), then the derivations would be 'beyond the scope of the course'. z
because gravity is aiding to the compression of the spring via PE, wouldnt it be a positive number? isnt d just a scalar?
the final height is below the zero of potential energy -- it must have a minus sign on it to account for the reduction in gravitational potential energy as you go below the chosen zero height. z
Can we solve it if time is unknown and Velocity is unknown as well but height at end is defined?
Thank you so much I would have died without this 😭
i want this code
I could probably still find the code, but unfortunately it's written for wxMaxima - an arcane computer algebra system. I should translate it to python soon (now that I'm finally starting to learn it after about ten years of avoidance)
Thank you so very ❤