Mechanics. Kinematics. The English-language lecture by Dr. Nadezhda Andreeva

Hello! Let's start our short course of physics. Let's start with the mechanics, kinematics. Let's talk about motion.

The motion can be uniform and uneven. Uniform motion is a motion with a constant velocity. When a body travels the same distance at equal intervals. In this case, we can calculate the velocity if we distance divide by the duration of the period. Or find distance by multiplying velocity by duration of the period. Or, if we need to find time period, then we can the distance divide by the velocity.

With uneven motion, the body travels different distance at equal intervals of time. Uneven motion can be uniformly accelerated. This means that the body is moving with constant acceleration.

What is acceleration? Acceleration shows how quickly the velocity changes. Or the change in velocity over time. Alternatively, we can write it as the ratio of delta v to delta t. Or the change velocity over time. Acceleration can be either positive, then the velocity is increases, and negative, when the body slows down.

Let's transform the resulting formula. What is delta v? This is the change in velocity, or the difference between the final velocity and the start velocity. Let the initial velocity be v0, and the final velocity simply v. Then the following formula is obtained for calculating the velocity at uniformly accelerated motion.

How to calculate the distance? Let's draw a graph of velocity versus time. As you know, the distance is the area of the figure under the graph. Below the graph we see a trapezoid, and the area of a trapezoid is half the sum of the bases, per height. The bases are v0 and v. And height is time. Let's calculate the distance. Let's make transformations using the formula for calculating time at uniformly accelerated motion. We get the following expression for calculating the distance for uniformly accelerated motion.

These are the basic kinematic formulas. If we express the time from the first formula and substitute it into the second, then we can get another one, which is also useful to remember.

Репетиционные занятия с ребятами в академии P.E.S. ведет Надежда Анатольевна, кандидат наук.