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Ch. 1 Video Lesson

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High AP Physics today we're going to discuss chapter 1 representing motion the goal of chapter one is to introduce the fundamental concepts motion and review related basic mathematical principles  each chapter you will have the opportunity to watch some pre lecture videos produce but one of the authors of your textbook we normally watch these videos in class but if you are watching this video of the lesson you will need to go to the strength is excite and pull up this video on your calendar where you find your assignments  motion is a change of Anna Exposition or orientation with time the path along which an object moves is called the object's trajectory this semester we will study dimensional motion which is motion a straight line also study two-dimensional or projectile motion as well as circular motion in rotational motion  a motion diagram is a composite image showing the object's position at several equally spaced instant left I'm here we have 3 motion diagrams what can we infer about each of these  we should first note that all diagram represent one-dimensional motion while the skateboarder is moving at a constant speed we can see that the runner must be speeding up and car is slowing down this motion diagram shows Motion in two Dimensions with changes in speed and direction  we're going to pause for a moment and use motion diagrams to see if it can help us solve question motion diagrams are made of two cars both have the same time interval between photos which car ARB is go slower  now throughout these videos when we get to a quick check you might want to stop or pause the video until you get your answer and then resume the V know when you're ready to hear the correct answer  Sony's motion diagrams we can see that car a must be traveling slow the particle model of motion is a simplification in which we treat a moving object as if it what's mask we're concentrated at a single point  can we see a motion diagram of a car stopping with the actual picture of the car shown as well but in B it's the same motion diagram for were using the particle model will use a single. Instead of the car to represent object but we still have the same amount of time elapsed between each frame and the next so it shows that the particle model shows it car is still slowing down what is the particle model to answer a couple quick check questions two Runners jog along a track the positions are shown at one-second intervals which Runner is moving faster the video get your answer no taking a look Runner a must be moving faster because they the 50m in less time  they'll take a look at these two particle models two Runners jog along a track the times at each position are now shown which Runner is moving faster hear both Runners are moving the same speed because both Runners cover the 50 meters in the 10 seconds for a complete motion diagram we need to label each frame with its corresponding time as red off of a clock will symbol T to represent time  as you can see in the picture we can start our time wherever we want in order to simplify the problem in the top motion diagram were interested in the entire motion of the car so we assigned T is equal to 0 at the begin but in the second motion diagram if we're only interested in breaking the breaking part of the motion we will sign T's equal to 0 here  in order to quantify motion will need to consider changes in time which will call time in a time interval delta-t measures the elapsed time as an object moves from an initial position to a final position please note that what city is always positive let's say a friend wants you to come to her house she tells you she lives 5 miles outside of town is this enough information for you to get to her house no so what else do we need we need to know five miles from where a reference point or origin is a starting point from which we can measure distances  now if you know your friend list 5 MI from the courthouse this is better but it's still not enough lastly we need a direction from the courthouse if she said 5 Mi east of the courthouse this is a lot better information now remember to specify position we need a reference point which is the origin a distance from the origin and a direction from the origin  look at the picture shown we've added an axis to make it easier to analyze the combination of an origin and an axis marked in both positive and negative directions makes a coordinate system is very similar to our Cartesian plane we talked about when we discussed vectors  blachley we need to add a symbol to represent position in physics we use the letter X to represent position and in this situation we would have had miles as our unit that we put in parentheses  let's take a look at this example problem Jane walks to the right at a constant rate moving 3M first in three seconds at Tia's equal to 0 seconds she passes the x is equal 1 meter Mark draw her motion diagram from she is equal to a -1 second 2T is equal to 4 seconds since James moving at a constant velocity or constant rate we want to make sure that are particles are adults are spaced at equal increments we also need to Mark each time and since it's telling us to start at easygoing and -1 will make the first. T's equal to -1 seconds and then label the rest that we have our times marked we need to add our axes that's going to measure position in meters in according to the problem it said that Jane past the x is equal to the one meter Mark at 0 seconds Cibolo 0 seconds I need to make that the one meter mark working backwards this would mean that we had a zero meter Mark at T's equal to -1 seconds and then filling in the rest we could say to meters 3 meters 4 meters  and then five meters and here's a correct motion diagram from TZ to -1 seconds to tease equal to 4 seconds train walking to the right now that we can determine the position of an object we can define an concept called displacement a change of position is called displacement in this means displacement is the difference between a final in an initial position we can use the formula unboxing in to represent displacement since are we set position is represented with the letter X Delta X represent displacement which is equal to the final position minus the initial remember that displacement is a vector quantity which means is going to have a direction using the formula shown in the example that's represented on the board we will see that the initial position was 50 feet and a final was that 0 feet so plugging that in in the correct order we would have 0 ft - 50 ft which would give us -50 ft or we could indicate as the West Direction so our final answer would have been 50 feet to the west and noticed now that we know about vectors we would put order in Brackets the displacement Vector represents the distance and action of an object's motion from the starting position an object's displacement Vector is drawn from the Jets initial position to its final position regardless of the actual path followed between these two points please no That's a Some of the actual path is known as the concept of distance let's take a look at question Maria is at a position X is equal to 23 meters she didn't undergoes a displacement of -50 M that's her final position pause the video and get your answer resume at when you're ready to see if you're correct  going to The Forum displacement change in X is equal to the final position minus the initial position now we're going to substitute in from our problem and it said that our displacement was in -50 meters were looking for Maria's and final position her initial position was 23 m  solving what are algebra will find out the final position was -20 7 meters which is represented at letter A another quick check chosen Aunt zigzagging back and forth on a picnic table as shown what's the ants distance traveled and the Ants displacement we take a look at the zig zag motion we see that the ant travels a total distance 50 cm but will need to calculate the displacement using the formula given earlier  looking for displacement the final position of the aunt is at the 10-centimeter Mark the initial was at the 40 centimeter mark so the displacement of the ant will be in -30 cm and will use the negative to represent our Direction so the correct answer would be e  the last couple of Concepts that we need to discuss in chapter 1 speed and velocity  motion at a constant speed in a straight line is called uniform motion that your book uses blue arrows to represent displacement vectors well please take a look at the formula at the bottom of the screen this shows you how to calculate the speed of an object and to calculate the speed of an object is the distance traveled over the time interval a slightly different concept is velocity traveling in a straight line speed measures only how fast an object moves but velocity tells us both an object's speed and its direction let's take a look at the formula  on the right notice that velocity is calculated by taking the displacement by the time and we are found out the displacement is represented as Delta X in the time interval is going to be delta T go take a look at the picture the bikes have the same but not the same velocity why do you think that is will take a look at the diagrams bike one moving to the right and bike to is moving to the left velocity is a vector quantity so we need to be careful and realized that velocity also includes a Direction velocity vectors are now represented on the screen we represent the velocity of an object by a vector the points in the direction of the object's motion and its magnitude can be the speed when traveling in a straight line noticed the book uses green arrows to represent velocity and it used the blue arrows to represent the displacement  let's take a look at the zigzagging again and take a little bit different approach the end zigzags back and forth for 10 seconds on the picnic table now let's calculate the speed and velocity remember that speed is found by taking distance divided by our time interval while velocity is going to be the displacement over the time interval  so our distance from earlier was 50 centimeters over a time of 10 seconds but are displacement which down by taking position to minus position one was a -30 centimeters over 10 seconds  so are correct answers again at 5cm per second or a -3 cm per second for the velocity inside let's take a look at one more example Frank is walking East at T is equal to 12 seconds his position is at 25 M 5 seconds later he's at X's equal to 20 metres what's Frank's velocity so taking her information out a problem we'll see that thanks initial position was 25 meters win  it was at a time of 12 seconds but is final what position to was 20 meters 5 seconds later which would give our time of 17 seconds calculate the velocity velocity is  displacement divided by time so our displacement the final position minus the initial position / are changing time which would give us a -5 m / 5 seconds in our velocity being negative one meter per second now in this case are negative would have indicated East because it did say earlier that Frank was walking East that wraps up chapter one and we want you to realize that you are now assigned the chapter 1 homework on the mastering physics site these also correlate to the textbook problems that are shown below hope this video helps have a nice day

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