Kinematic Equations and Freefall - Concepts for Problem Solving скачать в хорошем качестве

Kinematic Equations and Freefall - Concepts for Problem Solving

In this video we go over kinematic equations for motion with constant acceleration. Then we look at a special case of constant acceleration when an object is in freefall where it only moves under the influence of gravity. Each kinematic equation that we look at will be missing one of the quantities that we use to describe motion. This means that we have various ways of solving for missing information without knowing everything. We discuss problem solving methods and how to use what physics you know about a given scenario to help you choose an equation and solve for the quantity you need. In freefall motion, we always know the acceleration because gravity always pulls objects toward the surface of the earth, or in the negative y-direction. This acceleration is called gravitational acceleration and is equal to 9.81 m/s^2. Since we are only considering kinematics in one dimension, or one dimensional motion, an object in freefall will fall into one of three categories: an object dropped from rest, an object launched vertically upward, or an object launched vertically downward. There are a few things we can notice about this motion. If the object is moving upward, it will eventually reach some maximum height. This occurs when the object is no long moving up, so the velocity at this point is zero. We can use this fact to help solve for information about the motion of an object. Also, if an object returns to the same height, because it accelerated the same amount on the way up as the way down, it will be going the same speed. This is true for every height the object moves through. And since the object will spend the same amount of time on the way up as the way down to return to the same height, this total time of flight is exactly double the time to reach the max height. These are all pieces of information that we can deduce from physics to use in solving problems. The key is that we must remember or notice these things as they won't be explicitly stated. Finally, it is important to remember a few things. The phrasing "dropped from rest" or "released from rest" means the object has no initial velocity. And as stated before, the time of flight is the total time in the air, not to be confused with the time to max height. Then we need to be careful to correctly identify the directions of velocity and acceleration which can be completely independent of each other. The direction of acceleration only depends on the change in velocity, not the specific values of the initial or final velocity. This is also true for the direction of velocity and the sign of the position. Just because an object is at a negative value for position does not mean it cannot move in a positive direction and vice versa. Specifically, if the direction of velocity and acceleration are the same, the object will speed up in the direction of acceleration. If they are in opposite directions, the speed will decrease and if they remain in different directions, the object will eventually stop. If the directions remain opposite still, the object will begin moving again in the direction of acceleration, and then we have the situation where they are in the same directions as above. Remembering these key ideas and familiarizing yourself with these quantities in one dimension will make two dimensional kinematics much easier. And then we will tackle the 2D analog of freefall, which is projectile motion.