Overview
This lecture introduces fundamental physics concepts related to motion, including the definitions and calculations for distance, displacement, speed, and velocity, emphasizing their differences and applications.
Describing Motion & Reference Frames
- Motion is described relative to a frame of reference, often using a coordinate system like the Cartesian plane.
- Numerical values and units are essential to quantify motion (e.g., distance in meters, time in seconds).
Distance vs. Displacement
- Distance is the total length traveled, always a positive value, and includes all segments of a path.
- Displacement is the net change in position, can be positive or negative, depending on direction.
- For round trips, distance is the total path length, while displacement is the final position minus the initial position.
- Example: If you start and end at the same spot, your displacement is zero even if your distance traveled is not.
Speed
- Speed is the average rate of motion, calculated as distance divided by time (speed = distance/time).
- Speed is always positive and has units of meters per second (m/s).
- Example: If a kingfisher dives 7.0 meters at 4.00 m/s, time = 7.0 m / 4.00 m/s = 1.75 seconds.
Velocity
- Velocity is displacement divided by elapsed time (velocity = displacement/time).
- Velocity includes both magnitude and direction, and can be positive or negative.
- Example: If an athlete sprints 50 meters in 6 seconds, stops, and walks back in 40 seconds:
- Sprint velocity = 50m/6s = 8.33 m/s
- Walking velocity = -50m/40s = -1.25 m/s (negative for opposite direction)
- Round trip velocity = 0m/46s = 0 m/s (displacement is zero)
Key Terms & Definitions
- Frame of Reference — A coordinate system used to measure position and motion.
- Distance — Total length of the path traveled, always positive.
- Displacement — Net change in position (final position minus initial), can be positive, negative, or zero.
- Speed — Average rate of motion, distance divided by time, scalar quantity.
- Velocity — Displacement divided by time, includes direction (vector quantity).
Action Items / Next Steps
- Practice distinguishing between distance and displacement in various scenarios.
- Complete example problems calculating speed and velocity.
- Review definitions to prepare for upcoming quizzes or assignments.