Physics - 1D Kinematics - Free Fall, Acceleration due to Gravity | Corey Mousseau | Skillshare

Physics - 1D Kinematics - Free Fall, Acceleration due to Gravity

Corey Mousseau

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3 Lessons (32m)
    • 1. PhysicsCourseOnline

      0:16
    • 2. Kinematics 7 Free Fall High School And Ap Physics 9

      11:46
    • 3. Kinematics 7b Free Fall Example Problems High School And Ap Physics 10

      20:05

About This Class

Physics is all about the world around us.  We live and experience physics every moment of our lives.  For most, we take physics for granted and never really truly understand how this amazing world works.  

This course is the next in a series of courses covering the physics topics of One and Two Dimensional Kinematics. 

Feel free to fall in love with physics through this awesome course on gravity - free fall!  In this course I introduce you to the concept of free fall as we explore the acceleration due to gravity.  

You might want to view my other courses prior to completing this course; the complete order in which my courses covering 1D and 2D Kinematics are as follows:

To be honest, I fundamentally believe every single human should have a basic understanding of physics.  This is especially true for anyone working or aspiring to work in any field even remotely connected to the STEM world.  This includes obvious professions such as scientists, engineers, and doctors, though also include many surprise fields such as law enforcement, athletic anything, computer science (and all related fields), law, animation, and much more.  

I am a high school physics teacher by day.  I create the majority of my videos for my own students.  My courses all follow NY State high school physics entirely, as well as the nationally renown AP Physics 1 & 2 curriculum.  AP physics is exactly the same thing as any algebra based college intro physics course.  

If there is enough interest I intend to share out all of my courses which cover all of the remaining topics associated with AP/College physics.

Transcripts

1. PhysicsCourseOnline: Are you interested in learning all about physics? Do you want to master the high school in AP curriculum? Whether you're a high school student or an entry level college student, this course is for you. Each syriza dresses every topic thoroughly with lessons, demonstrations, an example problems. 2. Kinematics 7 Free Fall High School And Ap Physics 9: Hey, Moosa, here. Let's talk about free fall freefall. Yeah, you know, think of the song, Of course. Re falling. I always think of it in this city to make me all But I always think of Tom Cruise and that Jerry Maguire movie just belting out to free phone. I don't know why, but you haven't seen it. You're not missing much. It's OK, in any event, freefall dealing with objects that are falling solely under the influence of gravity. OK, you know, we're gonna talk about gravity and more depth in a couple of videos. Probably a couple more than a couple decent ways that lines on the dynamics unit. That's the force due to gravity. You really need to know that the reason why the obvious of fungus causes a force acting on them. But right now, what I'm talking about is the acceleration as a result of that force. Okay, so free fall is the acceleration due to gravity. Now, a couple of things understand. This means the object must be traveling with the Onley acceleration. Acting on it is indeed gravity. In order for something be truly in free fall, Onley gravity can be acting on it. Okay, so we have to remove other forces such as air resistance. Or, um, let's say you're falling while also maybe slightly tethered by maybe a bungee cord of some sort. You might not be in complete freefall. Okay, um, there's some interesting things with this that I think a lot of human beings just don't know and don't realize that I need to help. Clarify. So let's get Teoh. What do we want to start? Let's go into the idea about objects of different mass. If I have one object with certain mass going to save little M and I have another object, Big M. I'm referring to these as being two different masses. Okay, so this object has a little mass in this subject has a lot of mass, and I made them also differing in the volume. And you know what? For the sake of being a true science, let's remove that extra variable of volume. And let's say both objects are the same physical size, the same volume, but they're just varying in mass, so one might be more dense than the other night. I don't know why I made it all squiggly like I just chose to. So this guy is a little mass, and this guy has a big mass. So we're talking maybe two different balls. One is made of a low density material, one of the higher denser material. Okay. And we release them from the same height above the ground. I will say this is the ground here. Okay, so this is a church. I have this line here, just the show that they're at the same spot ones not higher than the other. Okay. And I'm gonna release these guys at the same time from the same height. And you ask the average human being which one hits the ground first. What are they gonna say? What are you gonna say? Which one of these hits the ground first? A lot of folks will say the bigger mess. They're going to say this guy here with larger mass will get pulled down by earth at a greater value than this guy will, and therefore it will accelerate at a greater value. And so this one will experience a small and this will experience a bigger A. And this one will definitely win that race. They're wrong. And if you said it. Unfortunately, you're wrong. Was well, turns out and we could probably attribute this to Galileo. At least I think he's the guy that first quantified all this, but he may not be the 1st 1 I think of it. I do not know. Uh, turns out objects of varying mess will experience the same acceleration due to gravity at the same spot on Earth. They will both hit the ground the same time you say. There's no way that's true. I've seen it not. I've seen it different. I've seen lighter objects hit the ground much later than larger objects. That's what you're thinking, right? I mean, you've got this classic when you're racist and try to do some artistic work, which I'm not able to do. But you've got this classic, uh, hammer. That's my hammer, By the way, I failed physics. Art wanna one in college? I'm just not an artist. And for those out there, there is no physics. Aren't one a woman had to take? Maybe they should make that a class, though. I'll have toe get in touch with the colleges. In any event, this is a hammer, and this is a feather. Okay, so if I were to drop a hammer and a feather from the same height above the ground the same time camera obviously, is more mass in the feather. You will notice the hammer goes straight down the ground and the federal kind of like flutter on the way down. And you got to say to yourself, See, See, you're wrong. Mass does affect the ability for a barista. Accelerate down. But that's not it at all. This is not true. In fact, if I were to go under my true definition of free fall, it both the hammer and the feather left the ground the same spot. While they were truly undergoing free fall, they would hit the ground at the same time, so long as they fell from the same height. So why is it in real life, the feather doesn't hit the ground at the same time is the hammer And a lot of you probably know this you're sitting there are home yelling at me rainouts. You saying you're taking too long to get to this point? Yeah, it's because here on Earth and many other locations in this universe, there is gonna be an upward resisted force acting on both of these guys, but more on that feather. And that's a resistance. And that's not truly free fall if we're in free, Father is no air resistance. So on Earth, when we're dropping objects were not truly in free fall because the air resistance acting this feather on that feather with fluttered down. And so you might be thinking, Well, is there an experiment we could do in which we get rid of a resistance? Yeah, there is. And in fact, I encouraged to check it out. There's a bunch of videos online. Just type in feather versus ball in a vacuum or something of that nature YouTube, and you're going to see all sorts of cool videos in which we can evacuate the air out of a chambermaid. We put him in a big room or two, but I have a two little demo in Class A, and I suck out all the air of it. And lo and behold, both the, uh, lightweight object with Demo that I do in class is just a piece of paper and the heavier weight object. The penny will actually both hit the ground at the same time. Pretty cool. Keep that in mind. Mass does not affect acceleration. So maybe I should write that here Mass has no effect, and I was struggle with This is an effect or affect. I don't know. People always try to tell me too. I'm like it makes sense. Ones. They explain it to me. We'll have some memory thing. For some reason, my brain just doesn't remember that. So if its affect I'm sorry, Uh, in any event, Masses no effect. Where else should we go with this? Okay, let's talk about that whole. What is exceptional? Gravity bit first, millions more thoughts dealing with free fall acceleration due to gravity is the acceleration as a result of the force due to gravity from the earth and the mass, It's on the earth that we're investigating. So maybe you or me or the ball that were throwing And for most of that, most of the earth anywhere near that surface of that earth, we'll experience the same acceleration due to gravity. So we're gonna say a we're gonna be more specific and say a is little G the acceleration due to gravity. Matt's give me equal the negative 9.81 meters per second squared and that negative isn't necessarily required. What is the negative mean negative implies in the negative direction? So I'm gonna say down Technically, some physics teachers were probably yelling at me for saying This is always down its toward that planetary body. But in our frame of reference, that's down. So we usually treat down is negative. So it's negative 9.81 meters per second squared. But if we chose to make down positive than this would be positive because it's a vector and that sign is literally just say, I'm getting lazy here, right? Just using my finger here. It's kind of silly in this example that negative just simply is there for directional information. Okay, so really 9.1 meters per second squared now that 9.81 is the average acceleration due to gravity around the Earth. There is a few factors, and we're gonna learn about this a little bit more when you know the forces. Ah, the forces units. But there's a few factors that will affect exception due to gravity of a falling object or any object now to be the proximity to the earth is the biggest factor for us. So if we have higher altitude were further away from the earth or for maybe towards the equator, where bulges out a little bit more, we're a little bit further away from the center. And so there will be some localized variances in this acceleration due to gravity of my drop down to maybe 9.79 or even a little higher than 9.1. But on average, that's the value. Keep that in mind. Some texts get rid of that one, and it's just 9.8. Whatever. If you're in the AP class, you could even go ahead and call it 10 meters per second squared. And it'll help do your help with your quick math. Of course, you won't be completely 100% accurate when you do that, but it's pretty good. Okay, so solicit your gravity. 9 21 meters per second squared. All right, recap. Freefall. Only under the object is traveling on solely under the influence due to gravity, mass has no effect. So actually gravity on earth is 9.81 meters per second squared. Get that one back in the extent wicket. Some factors will affect that. Such as how far away from the center of that planetary body you are. Of course, if you go to a different planetary body will likely have a different acceleration due to gravity. So if you go to the moon will be much smaller cause moving smaller. Lastly, just a few little kind of little things will come back up. Mawr we get into ST Projectile motion. Uh, the object does not need to be going down to be under the influence of gravity. So if I were to take a ball and I were to throw it up in the air and have it trouble back down to meet and this top down view will make it very difficult to actually do so if I take this bond, throw it up, it stops and then it falls back down right up in the down. Okay? It's in free fall the entire time. It leaves my hands like right now it's in my hand. My hand is pushing up. It's not for you fall cause there's more than one force acting on it. More than one acceleration. But once it leaves my hand on its way up and then down the whole time it's in the air. Of course, assuming there's no air resistance, we're gonna call it negligible. There's a knob. It is a free fall so far to draw this ball out, and I'm gonna kind of have a go up. Say, it's got initial starting Velocity V right, And then you go up a little higher, these get decrease and then gets the tightest point. What's its velocity? Its highest point. The ball momentarily stops and then comes back down. So I'm gonna draw this to the right and in blue, just you concedes that downward journey on. So its velocity starts to increase in the negative sense the entire time that ball is in the air, so long as there's no other forces acting on it. It's get experienced everywhere the same acceleration. That's G Okay, so it doesn't need to be actually falling. If we're using kind of real life terminology in order for to be in freefall, it just needs to be under on Lee the influence due to gravity. All right. I think that's good for now. I'm gonna do some example problems. The next video. Thank you. 3. Kinematics 7b Free Fall Example Problems High School And Ap Physics 10: Hey, Moosa. Here, uh, gonna do some acceleration due to gravity problems. Make sure you write these down, Della. The work. She make the knowns list right out the equation solved. Do the whole thing. Don't just watch me do it. Practice is essential. So we have a chunk of ice breaking off a glacier and falling 30 meters before it hits the water. So we know the displacement is 30 meters. I'm gonna add to this. We know it's falling down, so I'm gonna go ahead and for this example on a rate negative 30. We know it's falling 30 meters, assuming it falls freely. How long does it take to hit the water time? Now, if you read it and you just write this tone, you're gonna be like, yeah, this problem can't be solved. We need to know three variables to find any other variable. Miley. No one. But this is where you should realize that we're not to give you a problem that's impossible to solve. Instead, you should think through and think OK, maybe I know more than what I know. Sometimes it's helpful to write down all five variables, so I'm gonna do that for this woman say V one V two, an acceleration and I think to myself. OK, well, let's just go through this list. Do I know the initial velocity lets you edit a chunk of ice, breaks off a glacier and falls 30 meters? Well, what do you think the ice is? Starting Velocity is right after breaks off the glacier. Yeah, you're probably thinking it. You know it. It's falling from rest. So we do know that variable its velocity. Zero in the beginning. Do I know the second velocity? Probably not. That's the velocity just before hitting the water. Don't get all silly and c zero. Yeah, sure. Once it hits the water, it probably slows down and stops. But we're talking about right before impact. We don't know that. What about acceleration? So I know the rate change of velocity joined. No, I mean, obviously it's it's falling 30 meters. It starts at zero meters for a second and it falls 30 meters. Something's changing its motion. It must be accelerating. And also it's kind of silly. What this worksheet is the acceleration due to gravity. So I should also trigger that you know, a But let's assume on a test on the line. You don't really know. There's nothing telling you. It's definitely a gravity problem. Think about it. Why does it fall? It falls because of G. I like to write a equals G. Which then I'm gonna rate equals negative. 9.81 meters per second. Squared again. If you're in, say, the AP class or college level class, you could get away with running this to negative 10. Just the simple A fire math. All right. We want to know how long it takes me. One time we have distance Initial velocity acceleration. I'm thinking the easiest route might not seem like the easiest route, but it is. Delta D is v I t plus 1/2 80 squared the V I zeros left gone. I'm looking for time, so I need to isolate t gonna multiply both sides by two. Then you divide both sides by the A You're gonna rewrite. I'm just gonna write this down. T squared is to death of the over a. I don't want t square. So to undo the square I've got take the radical of both sides something to say. Well, cause radical too radical T squared. His T single say T is equal to the square root of two Delta D over a. All right, let's go ahead and plug it in the square root. We gotta put everything underneath that radicals. Let's not screw that up two times. Negative. 30. Divine that by quantity. Negative. 9.81 It's important we have the negative in both these numbers because then it'll cancel out and will make its My radical is doable. Now also, make sure that it gives me positive time, which is necessary. All right. I am getting an answer of 2.47 seconds. Cool. I wanted to I could find the final velocity now at that point. But I'm not kind of a problem. Doesn't ask for I'm not going to it. Number two. What is the acceleration of a rock thrown straight upward on the way up? What is it at the top of its flight path, And then what is it on its way down? This is one that students all the time screw up because for some reason, students seem to think that the acceleration of Iraq changes and I know why they're doing it. They're saying it because the speed slows down and then speeds up. Therefore, the gravity or the acceleration must change but doesn't think about. We take a rock and we throw it straight up. It's good. Start off with a pretty high speed on its way up. It's going to start to slow down. The Why is it slowing down? Is the gravity that when it gets to its highest point, it's going to kind of stop instantaneously. Very, very, very, very instantaneous, Very short period time. It's gonna have no velocity at all. Does the rock stay there, though? I mean, if the acceleration was not there as well than the rock would just stay there, we were taking something and turn it up and then have it just literally hover there when it gets to its highest point. No, it's crazy. Then it starts to fall back down. Well, as it falls back down, it starts to gain speed. By the end of it, it's going down at the same speed it was going up. Excuse that little noise. Well, I'm not gonna redo it. And so acceleration is not the Seimas velocity. In fact, on a job acceleration, vector When blue we have the same acceleration vector everywhere in its path. Those arrows are also see the same size. And it turns out the answer. This is a is negative. 9.81 meters per second squared the entire time even you right now have an acceleration of negative 9.81 meters per second squared acting. You sure? Your net acceleration Zero Because there's something can sing it out. Your chair probably. But just don't confuse acceleration with velocity. Let's move on the next problem. All right, object thrown straight up falls back to Earth. This is one dimensional motion. We're not done with projectiles yet. Okay, When is its velocity zero A. B Does its velocity change direction and see Does acceleration due to gravity Have the same sign on the way up is on the way down So an object is thrown straight up falls back to earth When is its velocity zero? Think about it. So the object straight up eventually comes back down. Yeah, you're probably thinking it at its highest point. It has to stop momentarily, just like that rock pro. So we have an initial velocity up gets what's highest point the equals zero and then it starts to fall back down. So here the answer to A is at highest point B. Does its velocity change direction? Well, of course it does. Think about it if on its way up to its highest point and then falls back to Earth. So, yeah, it starts to go back downward. Yes, its velocity does changes direction after its hit, its highest point. See, does the extortion due to gravity of the same sign on the way up is that does in the way down. And this'd is again I think students just like to kind of our unintentionally mix up and jumble up there different vectors. A lot of students will say yes. Ah, lessons will say no in answer to this is yes, it does have the same sign on the way up a zit does in the way down. While the object is traveling up, gravity is pulling it down. When it's at its highest point, gravity is still pulling it down. And as it falls back down yeah, gravity is still pointing it down as move on number four, If an object is thrown straight up and air resistance is negligible than its speed. When it returns to the starting point is the same as when it was released. If a resistance were not negligible, how would it speed upon return? Compare with its initial speed. So I take a rock, throw it up, I start off with 10 meters per second, eventually get to zero velocity, and then it eventually falls back down and rate rate ran where it left my hand. It'll have the same magnitude of velocity, but down this is with no air resistance. Now we're gonna take that same rock. We're gonna throw it up in the air 10 meters per second. But now we're gonna give it a resistance and think of air resistance as a bunch of particles in the way bombarding it. What's it gonna do to that object? Is it gonna increase? Its speed is it could have no effect. Where is it? Could because it's speed to go down. Yeah, you probably know this, but just in case, a resistance or resistance in general will always impede the motion of the object. So it's always gonna try to slow it down so it will reach Ah, high point and it will fall back down. But it slowed down here, so it didn't get as high as it would have gone before. And then, as it's falling back down, it's once again meeting air resistance. It's gonna fall that same distance, but now it'll land at a lower speed. Probably. I don't know. I'm not going to put a number there. They don't have any quantities. I don't have anything to you quantify with this, but it's definitely gonna hit a lower speed, and I just answer the second part how the maximum height, which it rises, be affected. It simply won't get to the same height. It will stop sooner than it did before because we have a additional factor of a resistance acting. All right, I was going in the next problem. Calculate the displacement velocity at times 0.511 point five in two seconds for ball thrown straight up with an initial velocity of 15 meters per second. You want take the point of release of why initial, why value to being zero? Meaning we are, the object could go up and then it could actually fall. Below are starting spot so I'm going to save. My initial velocity is 15 meters per second, no matter what. For part a time. 0.5 seconds in all the scenarios the acceleration acting on it is G. So we're gonna write negative 9.81 meters per second squared for every single situation. OK, for a though the time is 0.5 on NBC. Indeed, the time will be different. We're gonna end up doing the same thing over and over again just to compare. And we're looking at the displacement and the velocity at each of these times. Okay, so this is kind of annoying to do, but it is important, so it's going to do that. So what is my change in displacement and what is my final velocity? Okay. All right. So I don't know what we want to do. First. Displacement or velocity, we could do independently from until every time soldiers do displacement going to said the displacement is equal to be won t plus 1/2 a T squared. My initial velocity is not zero. So I have to account for us. Listen, to make my math a little bit harder than I've been doing 15 times 150.5. It's positive. It's upward Plus. Now here's the thing. You gotta catch a is negative. It's negative. 9.81 so plugged that negative in or also it's getting, indicate that it's causing the office to go higher and higher and higher or faster, faster and faster as it travels in here. That's simply not true. Times 0.5 spirits on Lee The 0.5 that's squared. Okay, Deposits of grip it right? I'm grabbing 6.27 375 meters into this around at 6.27 meters. Cool. So after 0.5 seconds, it's traveled 6.27 meters, its final velocity. After 0.5 seconds, I'm gonna find using V two equals V one plus 80. There's a couple ways that could have done it. This is the way I'm going to do it. So that's equal to a 15 plus negative 9.81 times 0.5. Let's figure that out and I'm gonna get 10.1 meters per second. That makes sense. It should be slowing down because it's on its way up, or gravity's pulling it down. Now we've got to do the same thing for both the blue and the purple equations here. But now, instead of using 0.5, I'm going to use 11.5 and two and said it me taking the time and wasting your time right now to rewrite everything with that, I'm just gonna do the same thing and I'm gonna plug in instead of 0.5. I'm going to the one the 1.5 to do that for both the equations away down the line. And I'm just get right out my answers right here. Now, just because I'm cutting corners here, which I'm not really doing just for the sake of this video doesn't mean you should take the time. Calculate thes all so you can get some information Here. Let me take the time to do this. I'll be right back. All right, be we're getting a distance of 10.1 meters. So still traveling up. It's higher than it was before. We're getting a velocity here, equal to positive. 5.19 meters per second. So, again, still traveling up is positive. Let's see what see has for us. See, I'm grabbing a height of 11.46 meters. So the displacement from the stars is always from the very beginning at 11.46 more meters. So we've only travelled about a meter, 1.36 meters in that last half second, which should make senses of going slower and slower and slower. Right? My average velocity here is actually quite low. It's only 0.285 meters per second. That means it's it's still positives was still traveling up. But it's just not at its highest point in its path. It's almost there. We'll see what happens. And I know a sanitized points path because its highest point, its path would be 00 I see a little error here. This is not an average velocity. I should be writing this down as a V two. It also it may have been appropriate for men. Right? VC here and VB here in V a here. Ah, it is. It is what it is. Let's see what d is. Okay. D is interesting. D m getting a displacement of 10.38 meters. Okay, That means it started to actually fall back down. D is going to be a location in between where it was between B and C. Try to like draw this out for you. Afterwards. We can see this in a little bit better detail. Its velocity here is gonna be It should be negative, right? Because it's fallen. It's no longer a sigh as it was in part C, so it should be heading down. Let's see. Yep, negative indeed. I'm getting negative 4.62 meters per second, so that means it's traveling downward with that speed. But it's still above the position in which I threw it from Let me kind of sketch this out deposit. Will I do that? And I'll try to show you in a diagram, more or less. What's happening here? Alright, so I've kind of shrunk everything moving up the side and did this kind of not the best diagram. The whole world, some walking through in the very beginning, was 15 years per second upward. It then traveled Ah, 6.27 meters and now its velocity. It for party is 10.1. It still traveled up at part B. Its velocity was still positive. 5.19 meters for seconds. This is at the 10 meter mark or so and then Let's see. It was still heading upward, but it was really small issue. See, my vectors are shrinking as I go up and the distance travelled between each segments, decreasing as well, and so its velocity apart sees only 0.285 meters per second. Then d we saw that I had a negative losses. What's traveling back down? And here it's actually at the 10.38 meter mark, which is in between C and B and it's headed back down negative 4.6 meters per second. Wow. Okay, this completes number five. This was a long one, huh? Let's see what number six has for us. Six. Basketball referee tosses the ball straight up for the starting tip off. What philosophy must have asked what player leave the ground to rise 1.25 meters above the floor in an attempt to get the ball? We want no want initial velocity. We'll get a basketball player to travel 1.25 meters as they're under the influence of gravity to catch that ball, and this is just basically the minimum velocity. So we're going to say at that highest spot, but it catch that ball velocity is zero. Ah, so this is gonna be V two squared equals V one squared plus two a Delta D. We're gonna look for V two, so I'm just gonna save you two is gonna be the square root of our weight. New when we're talking about we're not looking for V two. V two is the zero value. Looking for V one V one is gonna be the square root of negative to a Delta DEA subjected its hold to term over and I radical did. So let's give me the square root of negative two times negative 9.81 times a height of 1.25 This will equal I'm getting a velocity of positive 4.95 meters per second. So if they travel with initial burst of that speed, they should be able to get that. And for number seven, the Dolphin Aquatic shows I'm straight out of the water with a velocity of 13 meters for a second. How high does the dolphin travel and how long it in the air? We don't have enough information. Yeah, we do. Let's see they get into their highest point. How high did they travel at their highest point in the influence of gravity? Their velocity. Zero. Well, wait under the influence of gravity. I guess that means we also have an acceleration. Acting honest of negative. 9.81 meters per second squared. Whoa! All over the place there. Okay, so let's plug it in. What Self for displacement first? Sure. Why not? Do v two squared is V one squared plus two a delta d I saw for D, so I'm gonna say V two is your I'm gonna subtract that v one squared over. Divide that to a to show that Delta D is equal to Ah, well, let's see, It's give me equal to negative 13 squared over two times negative 9.81 And that'll equal no equal 8.61 meters Sweet The time the dolphins in the air can be found by cross multiplying . Well, if a I'll do the first a equals Delta V over t. So t will be Delta V over a. So it's give me my change in velocity. Well, final minus initial zero minus 13. So it's a negative 13 divided by negative 9.81 That ended up being 1.33 seconds. All right, cool. That does it for free fall problems. I hope this helps. I hope that you were able to follow everything. If not, just go back through, slow it down and re watch it. Think.