PHY1101 Lecture 1 - Kinematics 1

The lecture introduces Physics 111, focusing on kinematics, the description of motion. Physics explores matter, its fundamental constituents, their motion, interactions, and evolution through space and time, from the microscopic to galactic scales. Physics is compared to mathematics, essential for a deep understanding, requiring skills in algebra, trigonometry, functions, and vector manipulation. The importance of understanding fundamental physics for applied sciences like econophysics and neuropsychics is highlighted. The course will primarily use SI units, with occasional customary units, requiring basic unit conversion skills.

Motion is fundamental to the universe. Kinematics focuses on describing how things move, while dynamics explores why they move. The course mainly covers linear and some curved motion. To study motion, a reference frame with Cartesian coordinates (x, y, z) is used, with flexible choices for origin and axis orientation, provided consistency is maintained. Position is relative, not absolute, depending on the observer's reference frame. Displacement is the change in position (final minus initial), distinct from total distance traveled. Velocity includes both speed and direction, being positive or negative in 1D, while speed is always positive. Average velocity is displacement divided by time, and instantaneous velocity is the derivative of position over time. Average speed is distance traveled divided by time, and instantaneous speed is the absolute value of instantaneous velocity.

Uniform linear motion is characterized by constant velocity (and therefore speed). In this case, position changes proportionally to time, and displacement is velocity multiplied by time. Two common misconceptions are addressed: that distance traveled is always proportional to time (only true for uniform motion) and that constant speed equates to uniform linear motion (constant velocity implies uniform linear motion, but constant speed can occur in non-linear motion, such as circular motion). Understanding the difference between velocity (a vector with magnitude and direction) and speed (a scalar, magnitude only) is crucial.

Acceleration is the rate of change of velocity, including both its magnitude and direction. It can be positive or negative, indicating whether velocity is increasing or decreasing in the chosen positive direction. Average acceleration is the change in velocity divided by the elapsed time, while instantaneous acceleration is the derivative of velocity over time. The units for acceleration are length per time squared (e.g., meters per second squared). Several misconceptions about acceleration are discussed: negative acceleration doesn't always mean slowing down, velocity and acceleration are not always in the same direction, and zero velocity does not necessarily mean zero acceleration (e.g., at the peak of a thrown object's trajectory).

Uniformly accelerated motion describes movement with constant acceleration. Equations are presented for position and velocity in this scenario, incorporating the acceleration term. A useful derived equation relates the square of velocity to displacement. Uniform linear motion is a special case of uniformly accelerated motion where acceleration is zero. Freefall is a prime example of uniformly accelerated motion, where neglecting air resistance, all objects near the Earth's surface accelerate downwards at approximately 9.81 m/s² (little g). The sign of 'g' depends on the chosen coordinate system (e.g., negative if up is positive). Historical experiments by Galileo demonstrating the universality of freefall are mentioned.

For more complex scenarios where motion types change over time (composite motion), the problem should be divided into distinct phases. Within each phase, either constant velocity or constant acceleration equations can be applied. The final conditions (position, velocity) of one phase become the initial conditions for the next phase, allowing for step-by-step problem-solving. It's crucial not to apply a single set of equations across the entire motion if acceleration isn't constant throughout. A problem-solving strategy guide is offered for students to review and utilize.