Physics Concepts Overview

Overview

This lecture introduces fundamental physics concepts including displacement, speed, velocity, acceleration, projectile motion, and Newton’s three laws, with definitions, examples, and key formulas.

Distance & Displacement

• Distance measures how far something has traveled and is always positive (scalar).
• Displacement measures change in position and includes direction; can be positive or negative (vector).
• Displacement = final position - initial position.
• Example: Walking 8 meters east then 3 meters west results in 11 meters distance, 5 meters displacement (east).

Scalar vs. Vector Quantities

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

Speed & Velocity

• Speed is how fast something moves; always positive; scalar.
• Velocity is speed with direction; can be positive or negative; vector.
• Average speed = total distance / total time.
• Average velocity = displacement / total time.
• Example: If displacement is negative, velocity is negative (moving in the negative direction).

Calculating Speed, Velocity, and Time

• Formula: distance = speed × time (d = vt).
• For velocity: displacement = velocity × time (if direction is considered).
• Example: An object traveling 1000 meters at 50 m/s takes 20 seconds.

Acceleration

• Acceleration is the rate of change of velocity (Δv/Δt).
• Positive acceleration increases velocity; negative acceleration decreases it.
• Formula: acceleration = (final velocity - initial velocity)/time.
• When acceleration and velocity have the same sign, object speeds up; opposite signs, object slows down.

Gravitational Acceleration

• Earth's gravitational acceleration (g) is -9.8 m/s² (acts downward).
• Gravitational acceleration affects only vertical (y) velocity, not horizontal (x) velocity.

Projectile Motion

• A projectile moves under the influence of gravity.
• In projectile motion, horizontal velocity (vx) is constant; vertical velocity (vy) changes due to gravity.
• At projectile’s highest point, vy = 0; vx remains unchanged.
• Initial velocity components: vx = v·cosθ, vy = v·sinθ (θ = angle).

Newton’s Laws of Motion

• First Law: Objects at rest stay at rest, and objects in motion stay in motion, unless acted upon by a force.
• Second Law: Net force = mass × acceleration (F = m·a).
• Friction opposes motion, slowing moving objects unless eliminated.
• Applying a net force causes acceleration, increasing the object’s velocity over time.

Key Terms & Definitions

• Distance — Total length traveled, scalar.
• Displacement — Straight-line change from start to end, vector.
• Scalar — Quantity with magnitude only.
• Vector — Quantity with magnitude and direction.
• Speed — Rate of distance change, scalar.
• Velocity — Rate of displacement change, vector.
• Acceleration — Change in velocity per time unit.
• Projectile — Object moving under gravity’s influence.
• Force — A push or pull on an object.
• Friction — Force opposing motion.

Action Items / Next Steps

• Practice problems on displacement, speed, velocity, and acceleration.
• Review projectile motion calculations using initial speed and angle.
• Prepare to study Newton’s third law and momentum for the next class.