The kinematics considers change of spatial position of bodies irrespective of the reasons which caused the movement. The body moves thanks to forces operating on it, and this question is a study subject in dynamics. Kinematics and dynamics – two main sections of mechanics.
Instruction
1. If in a task it is told that the body moves evenly, it means that speed remains to a constant throughout all way. Initial speed of a body coincides with body speed in general, and the equation of the movement has an appearance: x=x0+v∙t, where x – the coordinate, x0 – the initial coordinate, v – the speed, t – time.
2. Naturally, motion not always is uniform. The opportunity which is often considered in mechanics is the ravnoperemenny movement of a body. Such conditions assume continuous acceleration, both on the module, and according to the sign (positive or negative). Positive acceleration says that the speed of a body grows. At negative acceleration the body gradually slows down.
3. At the movement of a material point the speed decides on continuous acceleration by the kinematic equation of v=v0+v0∙t where v0 is initial speed. Thus, the dependence of speed on time will be linear here. And here coordinate changes eventually quadratic: x=x0+v0∙t+a∙t²/2. By the way, movement is the difference of final and initial coordinates.
4. In a physical task any equation of the movement can be set. Anyway, that from function of coordinates to find function of speed, it is necessary to differentiate available the equations, by definition, speed is the first derivative of coordinate on time: v(t)=x’ (t). That from function of speed to find initial speed, substitute in t=0 equation.
5. Sometimes it is possible to find acceleration of a body, applying laws of dynamics. Place all forces operating on a body. Enter couple of rectangular coordinate axes concerning which you will consider a vector of forces. According to the second law of Newton, acceleration in direct ratio to the applied force and in inverse proportion to body weight: a=F/m. In a different way it registers as F=ma.
6. Actually, force defines how the body will accelerate. So, force of draft will force a body to move quicker, and friction force will slow down it. It is important to understand that in the absence of any external forces the body is capable not only to be motionless, but also evenly to move in space. It is caused by inertial properties of weight. Other question is that seldom it is possible to reach the conditions which are brought closer to total absence of forces.