Overview
This lecture introduces mechanics as a major branch of physics focused on motion, forces, and conditions for stability, with an emphasis on kinematics and how to describe and interpret different types of motion.
Mechanics: The Basics
- Mechanics studies motion, the forces causing motion, and the stability (equilibrium) of objects.
- Main questions addressed: What moves? How fast? Why does it move? What keeps it stable?
Branches of Mechanics
- Kinematics: Describes how objects move (distance, speed, velocity, acceleration), without referring to forces.
- Dynamics: Explains why objects move (identifies forces and torques that cause/change motion).
- Statics: Studies objects at rest or in equilibrium, focusing on balanced forces.
Physical Quantities: Scalars & Vectors
- Scalars: Quantities described by magnitude and unit only (e.g., mass, time, length, volume, density).
- Vectors: Quantities requiring both magnitude and direction (e.g., displacement, velocity, acceleration, force, momentum).
Kinematics Concepts
- Motion: A change in position from a reference point.
- Distance: Total path length traveled; scalar quantity.
- Displacement: Shortest straight-line distance from start to finish; vector quantity.
- Speed: Distance per unit time; scalar.
- Velocity: Displacement per unit time; vector.
- Acceleration: Change in velocity per unit time; vector.
Interpreting Motion Graphs
- Position-time graphs: Slope shows velocity; flat = at rest, straight/linear = constant velocity, curved = acceleration.
- Velocity-time graphs: Flat = constant velocity, sloped = acceleration, at zero = at rest.
- Displacement is the change from starting to final position; at rest when the graph is flat; fastest when the slope is steepest.
Types of Motion
- Translational/Rectilinear: Straight-line motion.
- Rotational: Around an axis or circular path.
- Free Fall: Vertical motion under gravity; acceleration due to gravity (g) = 9.8 m/s².
- Projectile Motion: Combination of horizontal and vertical motion under gravity.
- Uniform Circular Motion: Motion in a circle at constant speed; direction constantly changes, requiring centripetal force and acceleration.
Other Key Concepts
- Centripetal Force: Center-seeking force keeping objects in circular motion.
- Torque: Twisting force that causes rotation; increased with greater distance (lever arm) from pivot point.
Key Terms & Definitions
- Mechanics — Study of motion, forces, and stability in physics.
- Kinematics — Describes how objects move.
- Dynamics — Explains causes of motion (forces).
- Statics — Examines objects at rest/equilibrium.
- Scalar Quantity — Magnitude and unit, no direction.
- Vector Quantity — Magnitude and direction.
- Distance — Total length of path traveled.
- Displacement — Straight-line change from start to end.
- Speed — Distance divided by time.
- Velocity — Displacement divided by time.
- Acceleration — Change in velocity per time.
- Free Fall — Motion under gravity alone.
- Projectile Motion — Motion along both horizontal and vertical components under gravity.
- Uniform Circular Motion — Circular path at constant speed.
- Centripetal Force — Force directed toward circle center.
- Torque — Measure of force causing rotation.
Action Items / Next Steps
- Prepare questions from today’s material for the next class.
- Review and understand differences between scalar and vector quantities.
- Practice interpreting position-time and velocity-time graphs.
- Anticipate deeper study of dynamics and statics in the next masterclass.