04_lecture

Chapter Overview

• Title: Making Sense of the Universe: Understanding Motion, Energy, and Gravity

Describing Motion

• Speed: Rate at which an object moves (e.g., 10 m/s).

• Velocity: Speed with direction (e.g., 10 m/s, due east).

• Acceleration: Change in velocity over time (units: m/s²).

Acceleration of Gravity

• All objects fall with the same acceleration due to gravity, approximately g = 10 m/s² on Earth (ignoring air resistance).

• Galileo demonstrated that g is constant regardless of mass.

Momentum and Force

• Momentum = mass × velocity.

• Any net force changes momentum, indicating acceleration.

• Angular momentum relates to rotating objects.

Motion in Circular Paths

• Angular momentum refers to objects moving in circles; requires torque for change.

Mass vs. Weight

• Mass: Amount of matter in an object.

• Weight: Force exerted on an object by gravity (you are weightless in free-fall).

Newton’s Laws of Motion

• First Law: An object remains at constant velocity unless acted upon by a net force.

• Second Law: Force = mass × acceleration or change in momentum.

• Third Law: Every action has an equal and opposite reaction.

Gravitational Concepts

• Gravitational force is weaker on the Moon, affecting weight but not mass.

• Weightlessness in space results from free-fall.

Conservation of Energy

• Energy cannot be created or destroyed; it can change forms.

Types of Energy

• Kinetic: Energy of motion.

• Potential: Stored energy (gravitational potential energy depends on mass, gravity, height).

• Mass-energy: Represents energy contained in mass, described by E=mc².

Gravitational Dynamics

• The strength of gravity depends on the mass of objects and the distance between their centers.

• Newton's law of gravitation states every mass attracts every other mass.

Orbital Mechanics

• Orbits can be bound (ellipses) or unbound (parabolas, hyperbolas).

• Newton's laws allow calculation of total system mass from orbital characteristics.