Relative Motion and Inertial Reference Frames 

Thank you for speaking slowly and clearly unlike others in the profession of RU-vid science presenters who seem to speak at the speed of light.

WOW!! This guy is very good.. I been struggling with this for days, reading a lot and getting more confused. He made it simple to understand. Why cant more teachers do this???

Those great animations must have taken a lot of time to animate. Great job.

DUDE THIS WAS THE MOST SIMPLEST EXPLANATION ever, many thanks!!!!

"The Milky Way galaxy is moving through the universe at 230 km/sec" Relative to what?

I'm a high school student and I came to this video because pf my Physics teacher. He already mentioned the video was great but I didn't imagine it that GREAT. Professor Dave, you have a new great fan! You actually have solved all my doubts I had with this term. THANKS!!!!!!

When we stand still relative to the object, we are taking it's reference frame. Inertial reference frames are the frames that does not accelerate relative to other inertial frames. An easy way of testing inertial frames: take any object and release it in mid-air. If the object stands still, your frame is inertial.

this video was so so helpful! you make learning the topic easier cause you speak slowly, have colorful pictures/animations to illustrate your explanations, and emphasize definitions. thank you for packing my 2 hour physics lecture into 6 minutes!

None of the explanations in my native language helped me understand the topic and this video did help me. Thanks, Professor Dave.

Prof.Dave yo rock Remember, you could be the best teacher the humanity has ever seen ... Cause ya shrunk a hour class into 6 mins and still it is well understandable

Simple, straight forward and with illustrations that make sense. Excellent video. Thanks.

This was really confusing in the textbook, but this video made it infinitely easier to understand, thanks

This is way better than Crash Course or Khan Acadamy!! Thank you so much!

Visualizations are very important in learning. Thank you for the animations - they drilled the concepts home.

Holy crap never have I understood inertial reference frames as I do now. Thanks a lot for this! Every explanation of inertial reference frames I saw were so complicated and confusing to understand.

3:36 the ball does have the horizontal velocity of the train... The important point is you do too... So with respect to you... The ball remains at rest.. correct me if I am wrong..BTW you help us a lot man!🥂

I love the way the car just honks at you cuz you're explaining physics in the middle of the road

Beautiful, easy to understand, and efficient explanation! I also appreciate your enunciation. You are incredible! Thank you for creating such phenomenal educational content! 💓💓

Thank you Science Jesus

Another way I like to think of it is that when you are on a train and are moving away from the platform, it looks like the platform is moving and the train is staying still, so the train and the platform are both the inertial reference frame.

GOSH, I've never seen anyone explained the concept so clearly.. Concepts puzzled me for years finally gotten solved! Thank you so much.

I would recommend those who are only being introduced to this concept to take a look at the amazing properties of Einstein's Relativity. Great videos! Love your channel!

Thank u, it's been days I have been watching one video over other, this resolves my problems

I read few Physics books to understand this and you explains this so well ! Thank you !!

You just explained the same concept in 6mins that took my physics teacher 3 months. It was so simple to understand?????

Brilliant video, only one mistake is that Earth is not an inertial frame. Rather, Earth is a non-inertial frame of reference. A frame of reference is an object or a system that is used as a standard for measuring the speed of objects. A non-inertial frame refers to any reference frame that is accelerated with respect to an inertial one.

Fantastic, thank you! I was struggling to understand the textbook's explanation of an inertial frame, and you described it perfectly! :)

I really like the element of history included in teaching to show how humanity discovered something abd how we know it to be true . Without understanding history certain parts of the present are not comprehensive. I recently watched Veritasiums video on depressed cubics and how to solve them

Come on sir go back 6 years😂

Really appreciate how you put in so much effort in the animations to make stuff way easier for us 🥰

You explain better in 6 minutes than a book does in 1 week

I literally just now understood how time is relative in spacetime and how events can be perceived differently by different observers in that context. thank you

Your explanations and diagrams of basic concepts in physics are wonderful. I have used them to teach my children.

If you were born on a plane (600 mph ((relative to the ground)) and 10,000 m altitude at the equator) that never had to land, what would the difference in age be between someone traveling east and someone traveling west in 50 years?

the best explanation yet. thank you!

You nailed it Professor Dave..loved it.

I FINALLY UNDERSTAND THIS THANK YOU SO MUCH IT'S BEEN YEARS

Wow, this is well made. Good job, Professor Dave.

Can you please explain in details how a fly soar around very casually inside a car that is going around let's say 120 km/hr.? I mean the flies don't go up and down like the ball you showed here in animation, they are going all the ways and up and down and right and left? It will be much helpful.

I appreciate your explanation. I learned a lot today.

you are simply amazing ..... was tired and confused after watching so many contents....but you made it all easy ..... love from india **** sir

Videos like this deserve a love button. Like just doesn't express the gratitude.

Excellent explanation! My book was not very helpful for this section and basically just gave me an equation without going into almost any detail.

thank you so much...now i finally understood inertial frame of reference

Great explanaition; you make things look much simpler!

This was the best explanation for this phenomenon! Thank you

Dear man I appreciate your work, I would love if you would make a video about energy in reference systems

I like professor Dave, he is so pure and positive man!!!❤️❤️

simple yet understandable explaination for a very complicated topic.....thank you

Seriously..mind blowing explanation 😀

The best intro ever

By the logic discussed in this video then isn’t it perfectly legal to say that the earth is the center of our solar system and the sun does revolve around us if we take our planet as the inertial reference point?

Great video. Small correction Gallaeo didn't get in trouble with the church for saying the earth revolved around the sun. He got in trouble when he tried to teach that the moon had nothing to do with the tides on earth, which we know to be false. (My church still should have stayed out of the matter, but the point is that he didn't get in trouble for teaching a theory about the sun but for teaching an incorrect theory about the tides as truth.)

OMG !! You seemed to be like a mirror for me which displayed everything and made my views vast........... Just Thanks sir 🙏🙏Love from India ♥️

Thank you sir I was very eager to learn this my i completed 90 % of my internet but finally I learned because of u

just wondering, I have been told that the speed of light is absolute, but relative to what? it doesnt speed up if the light is coming out of a headlamp of a moving vehicle, but what is that relative to. If the speed of light is absolute, then could it be at a different speed in a galaxy that is moving at a different speed relative to us?

It's really a good one , specially the animations were more relative to the frame of understanding 👍

Thank you very much, my "PHD" professor briefly covered inertial frames but this video was able to make up for her incompetence!

Solid explanation! Thank you

my confusion is cleared.thank you professor.

Thanks sir . I can now understand the inertial reference frame 😀😀

Thank you Professor Dave!

2:09 TANK U SIR, the damned book told me two tests to run to see if the reference frame is inertial, talking about some mumbo jumbo when it's this simple to explain.

Excellent explaination 🙌

Daora parça, fortaleceu aqui nos estudos💪

3:10 Sir this example is explained by Stephen Hawkings in Brief History of time....you really are wonderful.

Explained so well! Thank you for this video. Keep uploading such videos

Let's talk about absolute position and reference frames. Positions that physicists calculate in each reference frame is a partial and ultimately incomplete calculation when it comes to position - in fact there is absolute position and all observers from each reference frames can agree on position if they have the proper equations gauges, sight, and instruments of all kinds. Absolute position is calculated by taking into consideration all the reference frames or the total reality of say a ball bouncing on a moving train. All viewers from every reference frame can agree with equations a gauges etc. As stated. For instance - a ball bouncing on a moving train - observer 1, a person standing at the side of the train tracks - observer 2, a person in outer space that is motionless. The person that is motionless in space sees all reference frames and can calculate absolute position quite easily - but infact they can all read or detect all reference frames to to the calculation, like the person on the train with a telescope that sees the person motionless in space, has a compas, has a speedometer, sees position outside looking through the window and all equations. The fact is they will all agree on position if the calculation of position of the bouncing ball is completed fully with all the reality behind the bouncing ball - all reference frames - which can all be detected and calculated- that is absolute position. Everything else I like to call a relative position - which ultimately are incomplete calculations of actual or absolute position.

wow, I won't be needing another video anymore. Hallelujah

I do not clearly understand what is meant by "so it's not completely wrong to say that the car is actually moving with this incredible speed as well, meaning that in a certain context, there'snpractically no difference between flying in a plane and sitting still in terms of absolute velocity. "

Thanks so much for the super good explanation!

his intro is probably the best intro I've ever seen

Professor Dave Explains - Two ping-pong players on a train going 60 hit the ball to/fro at 6 mph. A stationary observer near the train not within their inertial frame sees the game as the train flashes by. To he/she stationary observer, the ping pong balls are moving 60 mph. And NOT 6 mph...as the observer is not part of their inertial frame. Correct?

Much much better than any of the other videos😘😘

thanks prof dave. it helps me a lot. looking forward for more video tutorials.

Thank you Prof. Now I got a bit understanding in relativity (still studying)

The Weird Thing is, if you asked the outside observer what path the ball took, they'd say up and down, because we'd automatically and subconsciously assume the reference frame of the person we're asked about.

My favourite science teacher forever

But initially you said that the observor sees the ball taking a parabolic path because the ball had all the horizontal velocity(of the train) and then later on you say that the ball and the person throwing the ball up dont undergo motion but their surroundings do and hence the ball falls vertically downwards and has a vertical velocity only, kindly clear my confusion.

The ball in the train business. This is what I don't get. It seems that the ball in the box-car frame of reference is traveling a shorter distance than the same ball from the rail side frame of reference. Maybe I get it now. Each observer has a timer of the throw. Both clocks will read the same time. So the rail side observer sees the speed of the up and down motion plus the speed of the inertial motion.

This went over flat earthers heads. They need the version where you have a bunch of memes.

The intro creeped me out, but still subscribing for teaching topics very important for the humanity.

What would the free body diagram of the ball look like when it is in the air (when thinking about the example with the train)? Is there a horizontal force that acts on the ball in the direction that the train is also moving?

3:00 So 2 wrongs make a right, got it. Seriously though, doesn't the work done by the car's engine distinguish between the motion of the car and its surroundings? The surroundings aren't burning petrol to move 100km/h in the opposite direction? And when the car is parked, so at rest relative to its surroundings, it's not burning fuel.

Thanks for this! Great content!

Just watched this video yesterday for 9th grade Physical Science.

Such a good explanation! Your animations are so easy to understand. Thank you❤

thanks so much for this! back to the textbook reading now that I understand this part!

What if the person on the moving train throws a ball out backward (trying to create a projective motion from his own perspective)? Is it possible that the person outside of the train would see the ball just moves vertically up? On one hand, I thought it's possible as long as the horizontal component of the speed of the ball is equal to the speed of the train. On the other hand, I just feel like this would be insane.

Thanks professor.I don't really understand everything you said.But,to a point I grabbed the relativity between the moving car and the observer.

Hello, Professor Dave. Please allow me to use this in my class.

I wish someone could explain how this relates to the portal paradox. I am confident that the portal moving towards a cube is the same as the cube moving towards the portal, but I just don't know how inertial frames of reference relate to environments on both sides of the portal. Why is it that an object only switches inertial reference frames after going through the portal?

This guy managed to explain something my lecturer took an hour to do in 6 minutes

Hi professor ,I have one doubt the Earth moves faster nearer to the sun and moves slower farther to the sun the velocity is not constant it is varying between some values so from your point of view Earth is an inertial frame of reference but the condition for inertial frame of reference it obeys Newton's I law (constant velocity) . please explain?.I am confused.

Sir how can I show that an inertial frame of reference has constant velocity...?

This was so helpful

if the top of the train was open and the ball was thrown up, it wouldn't have only vertical velocity right?

Caralho, como eu vou assistir se o vídeo ta em inglês? Professor doidão

1:26 . I think a have a headach

great explain