Neil deGrasse Tyson Explains Speed vs. Acceleration

[Music] jack neil all right i'm going to talk to you about speed versus acceleration i knew one day we were going to have to have this talk it's sit down chuck chuck i need to i need a word with you son i've been meaning to talk to you about speed versus acceleration you're of age now where this is the time don't worry there's nothing to be embarrassed about so there's a nice scene nice there's a rememberable scene in the movie top gun where they just came out of there out of their planes and they're holding their helmet and what what does one of them say to the other as they high-five each other i've got the need for speed okay i thought it was great i feel i feel the need for speed and i want to push back on that if i may up okay you want to push back on the need for speed yes i am oh no because i claim that their speed is almost irrelevant to what it is their ex their that's triggering their emotions really yeah yeah because for example right now uh at our latitude on earth the rotation of earth is carrying us due east at 800 miles an hour are you saying i feel the need for speed and this is great no that may explain why i keep throwing up every time every time i stand up it could be a reason why i volunteer so no but say see i'm about to say that what we think of as motion sickness is not motion sickness it's acceleration sickness okay okay so earth is in orbit around the sun 18 miles per second that all of these speeds are way faster than anything they're doing in their airplane this is true so if they're not really after speed wow 18 miles in a second in a second one second from my house i would overshoot the bronx i mean no i would overshoot brooklyn where i am right now you'd end up in the long island sound right in one second okay so you you live in jersey you cross the hudson river the width of manhattan all over brooklyn and then you come out and i can't get up water oh my god that's amazing so here's the thing when you are moving at constant speed your body has no idea you're moving at any speed at all okay it's only when your speed changes that you get some sense of motion and by definition when your speed changes it's an acceleration now in in my in physics an acceleration can be positive or negative in in the english language we have another word for when it's negative acceleration and it's just called what deceleration deceleration okay so so i might say acceleration in this in my next few minutes i mean increasing or decreasing it doesn't matter either positive or negative excellent acceleration okay when that happens you feel it and that's what you're reacting to all right by the way think of velocity okay so velocity a change in velocity is an acceleration but sup and a velocity has a direction right but suppose you're banking a turn your direction is constantly changing well if velocity has to have one direction now i'm changing the direction that's also an acceleration so here's my point when you're in a moving object no matter its speed if the direction or the speed changes you are accelerating and when you feel an acceleration your body is going to respond if you accelerate forward your body will be thrown backwards if you s if you decelerate quickly your body goes forwards if you bank a turn you lean against the door or breaks the person next to you in the front seat so that's how you know you're accelerating because your body is responsible responding in this way so these folks said i feel the need for speed it's because they're doing barrel rolls in their plane and upside down and all the stuff they're doing that's what they're feeling but if they were going perfectly at mach 1 2 3 4 or 30 they wouldn't be saying i feel the need for speed because that's not anything they would notice this was been the complaint about the lexus car when it first came out the lexus was a you know a luxury car and that ride was smooth i read one commentary and it said it's like sitting on your living room couch while you're driving your car that sounds lovely so nobody who feels the need for speed is buying a lexus they want a car that can bank turns and and go from zero to sixty in whatever how many seconds you're talking about that's an acceleration yeah but it doesn't sound good to say i feel the need for acceleration [Laughter] it's a celebration of acceleration now i just sound like jesse jackson you know that's what i'm saying it's because my man rhymes anything it comes out of his mouth celebration of acceleration keep alive okay so so that's all i'm trying to tell you so that's why they'll they will give top speed when you're buying a car they will give a top speed um but they will also give 0 to 60 or 0 to 50 in a certain amount of time so that is the change in velocity over a certain amount of time and so if you change velocity in less and less amount of time your acceleration is higher and higher and higher that's why they keep trying to drop the acceleration time then it's more ahead it's more head snapping now right yeah now tesla oh because it was high right but it'd be true for any well-made electric car will have very high acceleration yeah even at low speeds right teslas can accelerate zero to 60 in three four seconds right yeah yeah and i've been in it and you can feel it it's like yeah okay okay so now watch let's kick it up a notch you ready i don't think you're ready are you seated okay all right i'm seeing okay there it is i don't want to accelerate too fast i better strap it okay so if acceleration is the rate of change of your velocity okay so if that if you rate changes quickly you have high acceleration you will feel this response all the more okay all right if acceleration is the rate and change in your velocity what happens when you have a rate of change of your acceleration oh my goodness let me guess your head explodes yes well okay so if you have a rate of change of acceleration that has a term in physics is called the jerk okay all right so so watch this oh man that's great okay so watch what happens you ready go ahead um so i'm headed towards a brick wall i'm trying to come up with these examples on the spot headed towards your brick wall and so i should put on my brakes so you put on your brakes okay and while you put on your brakes you feel yourself you're leaning into the the shoulder strap okay when you hit the wall your body jerks forward because you had a steady slowing down of your speed until your speed went to zero instantly so that is a rate of change of your acceleration and then you feel a jerk okay but what why don't we run into a wall okay so the jerk is what actually does sort of musculoskeletal damage in an accident okay okay because we we can sustain an acceleration but when they say i have one g two g those are pure constant accelerations but if you go from one g to six g's in an instant your whole body snaps right that's this and so the jerk is one reverse and the same thing reverse correct that's so what you're basically saying is jumping out of a 20-story window doesn't kill you that's correct is it it's the if there were no ground right he's already fired man so so that's uh velocity uh acceleration and jerk so almost every and and there's some cars they say in this car you can feel the road if you ever test drive like a sports car they tell you that right well what does it mean to feel the road well if the if the road were perfectly smooth you wouldn't feel anything so the fact that the road has certain bumps the lexus wouldn't feel those bumps because the tires are adjusting to it but your sports car which has quote rigid suspension it is rigid enough so that you're feeling that all right so you and the road and the bumps and wiggles and the turns and twists on the road you're feeling it all nice you feeling it and so you get so this is what you like this is what you seek this is what the sports enthusiast is actually after even if they're not self-conscious of it because if they only want at high speeds you can just get on a you know get on a high-speed train and then you don't feel it because they're smooth no you want to you want to bank the turns and feel it that reminds me of a guy on the i was on the turnpike and a guy comes by on a motorcycle and he's already i'm doing 80 so he had to be doing a little faster than 80 because he came by me and then he pulls back on the throttle and pops a wheelie at 80 miles an hour and pulls off okay so and and i and i'm pretty sure he was like i feel the need for acceleration [Laughter] and with the high accelerating cars of course a constant acceleration is a is a one-time thing by the way you either press yourself back or forward or lean one way or another and any abrupt change in that creates this this jolt but even if you if you're if you're going at zero and then you floor it there is the initial head snap okay that's a very high moment of acceleration but then you stays that way until you like hit the brick wall and then you're snapping another way so anyhow i just put i'm just putting all this out there in case you didn't know so uh all i can say is please take neil's word for everything he just said let's not try the brick wall experiment for ourselves okay we're not responsible for anybody who crashes the car into a wall all right just take his word for it all right there it is once again chuck you've heard it here and i'm neil degrasse tyson as always keep looking up you

Channel: StarTalk

Views: 196,238

Keywords: startalk, star talk, startalk radio, neil degrasse tyson, neil tyson, science, space, astrophysics, astronomy, podcast, space podcast, science podcast, astronomy podcast, niel degrasse tyson, physics

Id: lssHN9pPO24

Length: 12min 26sec (746 seconds)

Published: Tue Jun 01 2021