Overview
This lecture introduces the concepts of linear motion in physics, covering distance and displacement, speed and velocity, and acceleration, with examples and definitions.
Linear Motion: Basics
- Linear motion is movement in a straight line.
- Object may change direction but overall moves along a straight path.
Distance vs. Displacement
- Distance is the total path length traveled, regardless of direction (scalar).
- Displacement is the straight-line distance from start to end with direction (vector).
- Displacement can be found by subtracting starting position from final position, taking direction into account.
Speed vs. Velocity
- Speed is the distance traveled divided by time (scalar).
- Velocity is displacement divided by time and includes direction (vector).
- Average speed uses total distance; average velocity uses total displacement.
Worked Examples
- Example 1: A ball moves 10 m right, then 10 m left, then 8 m left. Distance = 28 m; displacement = -8 m.
- Example 2: Ball makes a round trip back to starting point. Distance = 36 m; displacement = 0.
- Example 3: Walking 3 km north, then 4 km east. Distance = 7 km; displacement = 5 km (by Pythagoras), angle = 53.1°.
Acceleration
- Acceleration is the rate of change of velocity over time, calculated as (final velocity - initial velocity) / time.
- Formula: ( a = (v - u) / t ) where ( u ) = initial velocity, ( v ) = final velocity, and ( t ) = time.
- Unit for acceleration is m/s².
- Zero acceleration means either stationary or moving with constant velocity.
- Positive acceleration: increasing velocity.
- Negative acceleration (deceleration): decreasing velocity, or increasing speed in the opposite direction.
Describing Motion
- Use terms: "stationary," "constant speed/velocity," "increasing speed/velocity," "decreasing speed/velocity," "constant acceleration/deceleration."
- "Constant" and "uniform" mean the same thing in describing motion.
Key Terms & Definitions
- Linear Motion — movement in a straight line.
- Distance — total path length traveled (scalar).
- Displacement — straight-line change from start to end point (vector).
- Speed — distance divided by time (scalar).
- Velocity — displacement divided by time, includes direction (vector).
- Acceleration — rate of change of velocity per unit time (vector).
- Deceleration — negative acceleration (may mean slowing down).
- Scalar — quantity with magnitude only.
- Vector — quantity with magnitude and direction.
Action Items / Next Steps
- Review the concepts of scalar and vector quantities if unsure.
- Practice calculating distance, displacement, speed, velocity, and acceleration with sample problems.
- Learn and memorize the formulas and units discussed.