Newton's 2nd Law of Motion (Knowledge Box #4)

Isaac Newton's second law of motion is one of the most universally recognised equations of all time, possibly second only to e=mc^2. Using this beautiful formula, we can deduce exactly why objects of different masses will accelerate towards the earth at the same rate during free-fall. It gets a bit mathsy, but stick with it.

@TheKnowBox

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Twitter: @TheKnowBox

[jamiecahill]

I honestly don't have any criticism for this video. It was informative yet entertaining enough to keep me (as a person without much interest in science) interested. And I love the new little ending clips! Great job

[honeybison]

I thought the video was over and I was thinking to myself: what about feathers! Then you went on to explain. Very good video!

[timbit]

My favourite video is when Prof Brian Cox dropped a feather and bowling ball in the vacuum chamber. Amazing to see them land at the same time! Physics is awesome :)

[someoneunimportant]

Video: *starts*
Me: nice
Alex: *uses grams and not lbs or whatever*
Me: NICE

[andrea.dibiagio]

1. Assume that the accelleration is constant 1:16
2. Use Newton's 2nd law and constant accelleration to prove that the force is proportional to mass 1:24
3. Use Newton's 2nd law and the force being proportional to the mass to prove that the accelleration is constant. 2:04

[belladonnanightshade]

No, no, its sky man magic! How dare you use this "science" to make sense of it. He works in mysterious ways, we are not to question.

[saltburner]

Not only is it astounding that a 17 year old can speak with such fluency, knowledge and understanding, but the production values of these videos is excellent. Presumably you have help from someone?

[IamGilgamesh]

Cosmic Skeptic, you have a wonderful camera presence. Your presenting skills are top notch. There is an error in your proof however. You use a cyclic argument to prove that acceleration is constant. You start by saying it is constant, and therefore mass and force are proportional. Then you plug in a couple of values of mass and force and get back the constant acceleration. This isn't a proof of acceleration being constant, merely a demonstration of it.

A correct proof would involve using F=ma, and then subbing in F=mMG/r^2, the formula for gravitational force. Alternatively, you could use the conservation of energy, and how gravitational potential and kinetic energy are both linearly dependent on mass.

[HeyItsKora]

1:06 this felt tip handwriting is SO good, not to mention how flawless those two lines are under the “150N”
Extremely satisfying haha

[unknown]

I can't even begin to tell you how helpful this video has been. Thank you very much.

[HeyItsKora]

Hahahahaha
“Once in a blue…. moon 🤔”
Cracked me up hahahah

[Respraysloth]

how many physicists does it take to change a light bulb?

two. one to hold the bulb, the other to rotate the universe.

[semiawesomatic]

May the mass times acceleration be with you

[Veganphobic]

I don't get it
So.
Earth pulls equally on each object based on its specific mass.

If the object is closer to earth it's pull is stronger.

But things always fall at the same speed as another thing
And
Things always fall at the same speed regardless of the distance from source of gravity.

So shouldn't things start off falling slower at high altitudes because the earths pull isn't as strong as distance increases?
I don't get if
And accelerate as they get closer because the force becomes stronger?

I don't get if
Objects have different maximum velocity.

I don't get it.

Do things accelerate when they sink in water?
What rate do things sink in water?

I don't get it

[adygombos]

Thanks for shedding some light on this topic.! So many people thinking that every object falls at the same rate on Earth just because they saw Veritasium's video which failed to mention air resistance.

[glutinousmaximus]

If you look at this question using Einstein's General Relativity, a suitably heavy object _does_ touch the Earth first (by an extremely small amount!) The reason is that the heavy object is also _pulling the Earth up slightly more_ than any very light object. You would have to do this experiment individually with each object and _very_ accurate testing conditions. If you drop the objects together, the heavier object is pulling the Earth 'upwards' so that both the objects _still_ hit the ground together!

[wild.rhino]

This guy is so good at explaining! This is why I love science. Just that feeling of "Aha" is amazing

[scottplumer]

My physics teacher would use two spheres of the same size, one of lightweight wood, the other of steel, to demonstrate this. He used the spheres so that the wind resistance would be the same. Great video, as always. Do you supposed the man with the dog in the background has any idea he's on YouTube?

[Kurt-zcmn]

If you want many practical examples of how wind resistance affects fall rate, look at skydivers or wind tunnel fliers. We're able increase or decrease our fall rate by presenting more or less surface area to the wind. Acceleration remains the same, of course, but terminal velocity can be changed quite a bit.

[shermaljones]

hi mate, im a new subscriber😃
Most of the things you talk about on your channal i already know or at least heard of but something about the way you present it makes it interesting to listen to.
good job CS👍