Basics of Motion in Physics

Overview

This lecture introduces the basic concepts of motion in physics, focusing on position, velocity, acceleration, and the main kinematic equations used to describe one-dimensional motion.

The Science of Motion

• Physics explains how objects move, using concepts like time, position, velocity, and acceleration.
• Motion in one dimension (straight line) is simpler to analyze than motion in two or three dimensions.
• Position can be positive or negative depending on the chosen direction; the choice of direction is arbitrary but must be consistent.

Key Motion Variables

• Time (t): measures how long motion lasts.
• Position (x): tells you where an object is along a line.
• Displacement is the change in position (Δx = x_final - x_initial).
• Velocity (v): change in position over time, including direction.
• Acceleration (a): change in velocity over time.

Graphing Motion

• Position vs. time graphs show how far you've traveled at each moment.
• Velocity vs. time graphs show how quickly position changes.
• Acceleration vs. time graphs show how quickly velocity changes.
• Units: Velocity is measured in meters per second (m/s); acceleration in meters per second squared (m/s²).

Kinematic Equations

• Average velocity: Δx / Δt (change in position divided by change in time).
• Average acceleration: Δv / Δt (change in velocity divided by change in time).
• Definition of acceleration: v = v₀ + at (final velocity = initial velocity + acceleration × time).
• Displacement curve: relates position, initial velocity, acceleration, and time (formula not explicitly given in transcript).
• For constant acceleration, these two main equations are essential; other equations are just rearrangements.

Using Kinematic Equations

• List known values (initial velocity, time, etc.) before solving problems.
• Use the displacement curve to find acceleration if needed.
• Use the definition of acceleration to find final velocity.
• Example: With v₀ = 0, t = 7s, and calculated acceleration, find final velocity and compare to speed limits.

Key Terms & Definitions

• Position (x) — where an object is located along a line.
• Displacement (Δx) — the change in position; x_final minus x_initial.
• Velocity (v) — rate and direction of change in position (m/s).
• Acceleration (a) — rate of change of velocity (m/s²).
• Kinematic equations — formulas relating position, velocity, acceleration, and time for constant acceleration.
• g — standard acceleration due to gravity, 9.81 m/s².

Action Items / Next Steps

• Practice identifying known values and choosing the correct kinematic equation for simple motion problems.
• Review graphs of position, velocity, and acceleration for different types of motion.
• Prepare examples of one-dimensional motion for discussion or homework.