[Music] thank you the theme of this video is space time and motion the topic is kinematics kinematics is the study of objects and their motion without consideration of forces this is a branch of classical mechanics in physics and the goal of kinematics is to use known or measured values of an object's motion and use mathematical models also known as equations to solve for other values of the object's motion to begin our understanding of kinematics we must start with three important values of motion when describing and analyzing motion the first important value to understand is position is the location of an object based on a reference point to determine the position of an object there must first be an agreed upon reference point a reference point can be any place in our universe and we often use reference points when we give directions without even thinking about it for example if you try to describe the position of the circle in this arrangement of shapes you would have to say something like the circle is located to the left of the triangle in this statement you have used a triangle as your reference point and the directional term left to indicate the position of the circle as it relates to the position of the triangle however someone else might say the circle is located to the right of the square this again indicates the same position of the circle but now it is in reference to the position of the square both of these statements indicate the position of the circle but use different reference frames therefore the direction of the position right or left of the circle is different in physics we use the coordinate axes to indicate a frame of reference and the origin of the coordinate axes is the reference point for the position of the objects we can look at the example of the shapes again but this time add an x-axis to show where these objects are located now we can see that the circle is at a position of zero meters or On the Origin the triangle is located at a position of five meters since it is five meters on the axis away from the origin and the square is at a position of negative five meters since it is located to the left of the origin which is defined as the negative Direction using the coordinate axes we can now identify positions of each object with a numerical measurement and direction positions however change and how much they change is an important value for physicists to measure and know we call these measurements displacement and distance we call a change in position in a straight line displacement displacement is a vector quantity that has a numerical value and Direction whose length is measured by finding the change in the position of an object and finding the length between those positions in a straight line the length is measured in meters however there is often confusion about the difference between distance and displacement distance is the scalar quantity and measures the total length traveled by an object whereas the displacement as we just mentioned is the change in position in a straight line we can illustrate the difference between distance and displacement by looking at the following example imagine you are traveling from your home to a restaurant that is one kilometer away when you reach the restaurant you would have traveled a distance of one kilometer and your change in position would be one kilometer from your home at this point the values of displacement and distance are equal now imagine you start to travel back to your home and halfway home you find an ice cream truck and stop to buy some ice cream at this point you would have traveled a total distance of 1.5 kilometers but your displacement or change in position from your home is only 500 meters now this illustrates the difference in the meaning of the values of distance and displacement velocity is another important motion value and it is the rate of change of position velocity is a vector quantity with a numerical value and direction that measures how much an object's position has changed over a period of time objects that have a large velocity value means that they have changed their position by a lot in a short period of time we refer to objects that move in this way as fast objects that have small velocity values have changed their position by a small amount in a large period of time we refer to objects that move in this way as slow consider a race between two runners they will both move their bodies and change their positions from the starting line or origin and move themselves to the position of the finish line this is a change in position the racer who moves their position to the Finish Line in the shortest amount of time will win and has a larger velocity than the other racer we can calculate the velocity of objects by using a mathematical model that divides the change in position also known as displacement by the length of time this results in a derived unit of measurement of velocity of meters per second however do not confuse velocity and speed speed is a scalar quantity that measures the distance traveled over a period of time the difference of these ideas is that speed will use the distance traveled in its calculation and velocity only uses displacement we have already discussed the difference between distance and displacement note however that speed and velocity will use the same derived unit of meters per second and that is often where the confusion can stem from there are two ways to think about velocity of an object one way is to think about how fast an object is traveling at that moment in time and the other way is to consider how fast the object has traveled over the whole journey both are important measurements and will be discussed now instantaneous velocity and speed is the measurement of how fast an object is traveling at any moment in time the most important example of instantaneous speed is the value you see when you are driving when you look down at your speedometer it is important to know what your speed is at that exact moment in order to measure the instantaneous velocity of an object you must know a small displacement over a small period of time traveled by the object and use the velocity equation to calculate the value this is different from when you measure average velocity and speed average velocity and speed are measurements of how fast an object has traveled over the whole journey to visualize the difference between these ideas of average versus instantaneous consider the motion of cars in their drivers as they commute in a city it might take a car 30 minutes to travel from one point to another the average velocity of the car might be five kilometers per hour because it took the driver 30 minutes to travel 2.5 kilometers but at any moment in time the car and the driver might have had an instantaneous velocity that was greater or less than the average velocity for the whole trip it just depends on what the traffic was like at any moment therefore depending on what a physicist might be investigating it might be important to know the average or the instantaneous velocity of an object sir the third important motion to be familiar with is acceleration which is the rate of change of velocity acceleration is a vector quantity with a numerical value and direction that measures how much the velocity of an object changes over a period of time this means when an object's velocity changes the object is considered to be accelerating an object's velocity can change by either decreasing or increasing if an object's velocity is decreasing that means the object's position is changing less and less as time goes on this means the object is getting slower if an object's velocity is increasing that means the object's position is changing more and more as time goes on this means the object is getting faster in both cases the object is accelerating because the value of their velocity is changing acceleration can be calculated using a mathematical model that divides the change in velocity by the length of time acceleration uses a derived unit of meters per second squared now that we have established the important values of motion position velocity and acceleration we can now see how they are used in combination to predict and solve for unknown values of objects in motion to model the motion of objects in importantly predict the value of different parts of an object's motion suvot equations also known as kinematic equations can be used with known information about the object's motion to find unknown values of the object's motion these equations use the set values we have already discussed displacement velocity acceleration and time and they are noted with the following symbols s u v a t they are arranged in the following four equations becoming familiar with which equations to use and when to use them is an important skill for this topic one important note is that these equations are only meant for objects that uniformly accelerate those are objects whose acceleration remains constant so far we have talked about the object's motion under uniform acceleration this is when object's acceleration stays constant however our world does not consist of only uniform motion and therefore we must consider objects that move under non-uniform motion as well examples of objects moving over non-uniform surfaces such as a runner moving over a hilly section of a run will result in the runner's acceleration changing as they move up and down Hills objects that move in circles and objects that are subject to air resistance will all experience non-uniform accelerations therefore for your problem solving is essential that you pay close attention to whether the object is considered going through uniform motion and if we are ignoring air resistance these are two factors that play a large role in the motion of the object and the suvat equations will only work for situations where the object is undergoing uniform acceleration foreign an example of understanding the importance of uniform and non-uniform acceleration is when we evaluate objects that are categorized as projectiles projectiles are objects that move in the vertical and horizontal dimensions the shape their path makes is the parabolic shape on the screen this shape is the result of the object experiencing two independent motions simultaneously the horizontal motion and vertical motion are independent of each other because the horizontal and vertical motion of the projectile are independent we can then calculate the vertical and horizontal motion separately from one another in the evaluation of projectile's motion you must be aware of if the object is moving in the absence of fluid resistance or if there is fluid resistance present if the object is moving in the absence of air resistance also known as fluid resistance we can assume that the horizontal motion of the projectile has a uniform acceleration of zero because as the object moves through the air there is no other object applying a force to cause it to speed up or slow down we can also assume the vertical motion of the projectile has a uniform acceleration of negative 9.81 meters per second squared due to the force of gravity causing the object to accelerate towards the Earth this can then lead to further calculations of displacement time and velocities that can be solve for using the Suva equations however if fluid resistance is present there are a number of effects that the resistance will have on the motion of the projectile when a projectile is moving through the air we must take into account the presence and effect of the air molecules making contact with the object as it moves let's start with the effects of horizontal motion the presence of the air will have a decreasing effect on the horizontal acceleration of the object this means that the object's velocity will decrease over time resulting in a shorter range or horizontal displacement of the projectile the effects on vertical motion are more complicated as the ball travels up the ball is making contact with air molecules which is causing there to be a greater overall acceleration effect downward causing the object to slow down faster as it moves up then as the object moves downward it again makes contact with air molecules but this time the molecules are pushing up against the downward acceleration of the object causing it to accelerate slower in the downward Direction the overall effect of the air resistance is that the flight time is decreased due to the reduction in Vertical Velocity in the upward and downward directions and the vertical height is also decreased the last thing to consider when taking air resistance into account is terminal speed when objects are falling for long enough time or have a large enough surface area they can reach terminal speed this is a speed at which the object stops accelerating downward and instead is moving at a constant velocity the way that this occurs is that the force from the air resistance is great enough that it matches the force of gravity pulling down on the object the result is that the object is no longer accelerating and has reached its maximum speed while falling [Music] thanks for sticking around to the end you if you want feedback on any of the answers please send us an email at electric learningyt gmail.com and we'll get back to you as soon as we can have a great day