Welcome to my series on AP Physics 1. Today we'll be covering Unit 1, called kinematics. Kinematics is the study of motion. Essentially, we'll be studying the relationship between five motion variables.
Initial velocity, final velocity, displacement, acceleration, and time. Before we start, It's worth going over the difference between scalar and vector quantities. A vector value has both a magnitude and a direction, whereas a scalar value only has a magnitude. For example, velocity has a magnitude, which is your speed, and a direction, whereas speed just has a magnitude.
Another example is displacement. If you travel along a path, your displacement is the distance from your start point to your end point, as well as the direction you would have to take to get there. In contrast, Your distance is the amount of distance you have traveled, which is a scalar quantity.
Of the five motion variables, four of them are vectors. Initial velocity, final velocity, displacement, and acceleration. Only time is scalar.
Finally, we'll define these five variables. Displacement is your distance and direction. Velocity is equal to displacement over time.
Finally, acceleration is equal to the change in your velocity over time. A large part of this unit is studying position time, and velocity-time graphs. We'll start with position-time graphs. On these graphs, position is in the vertical axis and time is in the horizontal axis. At any point, the slope of a position-time graph is equal to the velocity of the object that it's tracking.
If you've taken calculus, you'll understand this to mean that the derivative of a position-time graph is a velocity time graph. If a position-time graph is horizontal, it means the object isn't moving at all. If the If the graph is a straight line, the object is moving at a constant velocity.
which is equal to the slope of that line. If the line is going up, the velocity is positive, and if the line is going down, the velocity is negative. If the line is curved, it means that the object is accelerating, because the velocity of the object, which is the slope of the curve, is changing.
If you need to find the velocity of the object at a given point on a curved graph, you can divide the change in y value by the change in x value around that point. Next, we'll move on to velocity time graphs. The slope of a velocity time graph is equal to the acceleration at that point. Also, the area under a velocity time graph is equal to the displacement of the object.
If you've taken calculus, you'll understand this to mean that the integral of a velocity time graph is a displacement time graph. When analyzing these graphs, make sure you know whether it's a position time graph or a velocity time graph. A good hint is if it's curved. A velocity time graph won't be curved, at least on AP Physics 1. In addition to learning how to analyze graphs.
You'll also have to know how to manipulate the variables of motion using algebra. Luckily, there's five kinematic equations that relate all these variables. The most important one is a equals final velocity minus initial velocity over time.
This defines acceleration. If you look carefully these equations, you'll notice that each one relates four variables together and is missing one. For example, the equation that I just mentioned doesn't include displacement. This means that if you have any three motion variables, you can find the other two by using one or more of these equations. This of course involves doing some math.
A specific application of these formulas is projectile motion. This refers to all objects in freefall. When solving problems with projectile motion, it's important to keep in mind that you already know the acceleration. On earth, it's 9.8 meters per second squared towards the ground. An example of projectile motion is a rocket being shot up towards the sky with a given velocity.
A question might ask you how long it would take to hit the ground. If that seems easy, it is, but you'll also need to know how to evaluate projectile motion in two dimensions. For example, if an object is shot out of a cannon at an angle. To do this, you'll have to separate the velocity of the object into its x component and its y component.
This can be done using trigonometry. For example, if an object is launched at 5 meters per second with an angle of 30 degrees, Its speed in the x direction is defined by 5, the magnitude of the vector, times cos , the angle, and its y component is defined by 5 times sin . Determining the distance of a projectile launched at an angle is a popular problem because it requires a complete knowledge of kinematics. To solve this problem, first find the speed in the y direction of the projectile.
You can use this information to find how long the projectile stays in the air. Then, using the simple v equals d over t formula, You can determine how far it has traveled in the x direction. In conclusion, kinematics relates five motion variables.
Initial speed, final speed, displacement, acceleration, and time using the five kinematic formulas. If you have any three of these variables, you can use the formulas to find the remaining two. If you enjoyed this video, please consider subscribing to my channel.