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# Physics Notes - Movement of a System ## Chapter 1 **Theme 2** **I. System Displacement** **a. System and Reference Frame** * A system corresponds to the object being studied. * For simplification, the object can often be modelled as a single point, such as its center of gravity (G). * A refer...

# Physics Notes - Movement of a System ## Chapter 1 **Theme 2** **I. System Displacement** **a. System and Reference Frame** * A system corresponds to the object being studied. * For simplification, the object can often be modelled as a single point, such as its center of gravity (G). * A reference frame is the basis for describing the object's movement. * A reference frame consists of three components: * A reference body (e.g., Earth) * A spatial reference (e.g., coordinate system) * A temporal reference (e.g., time) * Any object can be a reference frame, but some are better suited for specific tasks. For example: * **Geocentric**: Earth-centered reference frame, suitable for short-term movements on Earth * **Heliocentric**: Sun-centered reference frame, useful for planetary motion * **Real-time**: a reference frame that gives an actual position within the given space and time **b. Velocity Vector at a Point** * During movement, velocity changes in direction, magnitude, and/or sense. * Average velocity doesn't capture these changes. * Instantaneous velocity approximates the velocity over a very short time interval: $v = \frac{\overrightarrow{MM'}}{Δt}$, where: * v is instantaneous velocity vector * $\overrightarrow{MM'}$ is displacement vector * $Δt$ is a very small time interval **Example:** * Figure shows real-time recorded movement (time interval = 40ms) **b. Trajectory** * Trajectory = the set of points occupied by the system during its movement. * A trajectory can have different forms (e.g., straight line, circle, curve) **c. Displacement Vector** * Displacement vector ($\overrightarrow{MM'}$) is the change in position from point M to point M'. * The direction is from M to M' * The magnitude is the distance between M and M' **II. System Velocity** **a. Average Velocity Vector** * The average velocity vector between two points at times t and t' is defined as: $\overrightarrow{v_{moy}}=\frac{\overrightarrow{MM'}}{t'-t}$ * $\overrightarrow{MM'}$ = displacement vector between M and M' * t' - t = change in time (seconds) **c. Relative and Nature of Movement** * A system's movement depends on the reference frame. * The characteristics of velocity vectors define whether a movement is uniform or non-uniform. **(Diagram) Table of rectilinear motion** | Feature | Uniform Motion | Non-Uniform Motion | |----------------------|-------------------------------------------|---------------------------------------------| | Velocity vector | Same direction, same magnitude over time | Varies in direction and magnitude over time | | Example | Motion along a straight line with constant speed | Motion along a straight line with changing speed | **(Diagram) Table of velocity vector** | Feature | Data Description | |-----------------|----------------------------------------------| | $\overrightarrow{v_1}$, $\overrightarrow{v_2}$, $\overrightarrow{v_3}$, $\overrightarrow{v_4}$| Velocity vectors at points M1, M2, M3, and M4 | **(Equations and Calculations)** * Various equations and calculations related to velocity, displacement, and time are shown in the document. Specific formulas are transcribed above when possible. * Additional figures and labels in document are used to illustrate the components of these calculations **Note:** The document contains handwritten notes and some parts are difficult to decipher. This summary is based on what is clearly readable in the available image extracts.