Physics Concepts Overview

Overview

This lecture introduces fundamental physics concepts including displacement, speed, velocity, acceleration, projectile motion, and Newton's three laws of motion.

Distance and Displacement

• Distance is the total path length traveled and is always positive (scalar quantity).
• Displacement measures the straight-line change from initial to final position, including direction (vector quantity).
• Example: Walking 8 meters east then 3 meters west means distance = 11 meters, displacement = 5 meters east.
• Displacement = final position − initial position.

Scalars vs. Vectors

• Scalar: Has only magnitude (e.g., distance, speed).
• Vector: Has both magnitude and direction (e.g., displacement, velocity).

Speed and Velocity

• Speed is how fast an object moves; it's always positive and scalar.
• Velocity includes speed and direction; it can be positive or negative (vector).
• Formula: distance = speed × time (d = vt); displacement = velocity × time.
• Average speed = total distance / total time.
• Average velocity = total displacement / total time.
• Example: 12 m east + 20 m west in 4 sec: avg speed = 8 m/s; avg velocity = -2 m/s.

Acceleration

• Acceleration is the rate of change of velocity over time (vector).
• Formula: acceleration = (final velocity − initial velocity) / time.
• Positive acceleration increases velocity; negative acceleration decreases it.
• If acceleration and velocity signs match, object speeds up; if opposite, it slows down.
• Gravitational acceleration on Earth is −9.8 m/s² (acts in vertical/y direction).

Projectile Motion

• A projectile moves under gravity's influence; gravity only affects vertical motion (vy).
• Horizontal velocity (vx) remains constant (if no horizontal force).
• Vertical velocity changes by −9.8 m/s each second on Earth.
• At the peak of a projectile's path, vy = 0 but vx remains unchanged.
• To resolve velocity at an angle: vx = v cos(θ), vy = v sin(θ).

Newton's Three Laws of Motion

• First Law: Objects at rest/motion stay that way unless acted on by a force (inertia).
• Second Law: Net force = mass × acceleration (F = ma).
• Third Law: Not covered in detail in this segment.

Key Terms & Definitions

• Distance — total path length traveled (scalar).
• Displacement — straight-line change from start to end with direction (vector).
• Scalar — quantity with magnitude only.
• Vector — quantity with magnitude and direction.
• Speed — rate of distance traveled (scalar).
• Velocity — speed with direction (vector).
• Acceleration — rate of change of velocity (vector).
• Projectile — object moving under gravity's influence.
• Gravitational acceleration (g) — acceleration due to Earth's gravity, −9.8 m/s².
• Net force — total force acting on an object.
• Tension — force applied through a rope.

Action Items / Next Steps

• Review differences between scalar and vector quantities.
• Practice using formulas: d = vt, a = (vf − vi)/t, F = ma.
• Try example problems on average speed, velocity, and projectile motion.