Chapter 2 Textbook Notes

Night Sky

Night Sky

The lights we see in the sky at night, including stars and planets.

Predictability

The regularity and predictability of the sky's changing patterns.

Ancient Observers

Early humans who noticed regularities in the arrangement and movements of stars and planets.

Astronomy

The study of objects in the heavens, one of the first sciences to develop.

Stonehenge

A prehistoric stone monument in southern England used to mark the passage of time based on the movement of objects in the sky.

Stonehenge as a Calendar

Stonehenge served as a giant calendar, allowing people to determine the seasons and when to plant crops.

Stonehenge Construction

Stonehenge was built by ancient civilizations without a written language or metal tools, relying on knowledge passed down through observation.

Spread of Disease

The discovery by John Snow that the incidence of cholera was connected to contaminated water, leading to the development of modern sanitation and public health systems.

Observing Nature

Observing nature is a crucial part of the scientific method, as seen in Snow's discovery of the connection between disease and polluted water.

Ancient Astronauts

The idea that ancient monuments like Stonehenge were built by visitors from other planets, which is considered pseudoscience by scientists.

Ockham's Razor

The principle that the simplest and most straightforward explanation is usually the most likely, leading scientists to reject the notion of ancient astronauts building Stonehenge.

Birth of Modern Astronomy

The observation of the distinctive motions of objects in the sky and the development of astronomical explanations by the Greeks.

Ptolemaic system

The geocentric model proposed by Claudius Ptolemy, where Earth is at the center of the universe and the planets and stars revolve around it on rotating spheres.

Copernican system

The heliocentric model proposed by Nicolaus Copernicus, where the Sun is at the center of the universe and the planets, including Earth, orbit around it in elliptical paths.

Tycho Brahe

A Danish nobleman and astronomer who made accurate observations of planetary positions using improved instruments, providing crucial data for Johannes Kepler's laws of planetary motion.

Johannes Kepler

A German mathematician and astronomer who analyzed Tycho Brahe's data and formulated three laws of planetary motion, including the discovery that planets orbit the Sun in elliptical paths.

Mechanics

The branch of science that deals with the motions of material objects, including the study of how objects move, change speed, and change direction.

Speed

The distance an object travels divided by the time it takes to travel that distance.

Velocity

The speed of an object in a particular direction, including both the numerical value of speed and the direction of travel.

Acceleration

A measure of the rate of change of velocity, indicating how an object's speed or direction is changing over time.

Acceleration

The change in velocity of an object over time. It can involve changes in speed, direction, or both.

Velocity

The speed and direction of an object's motion. It is a vector quantity.

Uniform motion

Motion at a constant speed in a single direction.

Galileo's experiment

Galileo conducted experiments to determine the relationships among distance, time, velocity, and acceleration. He showed that all objects fall at the same rate of acceleration regardless of their weight.

Inertia

The tendency of an object to remain in uniform motion. A body at rest tends to stay at rest, and a moving body tends to keep moving, unless acted upon by an external force.

Newton's first law of motion

An object will continue moving in a straight line at a constant speed, or remain at rest, unless acted on by an unbalanced force.

Force

Something that produces a change in the state of motion of an object. It causes acceleration.

Newton's second law of motion

The acceleration of an object is directly proportional to the magnitude of the force applied to it and inversely proportional to its mass.

Mass

The amount of matter in an object. It is a measure of the object's inertia.

Balance between force and mass

Newton's second law of motion defines the relationship between force and mass in producing acceleration. The greater the force, the greater the acceleration, while the greater the mass, the smaller the acceleration.

Newton's First Law

Defines force as something that causes a mass to accelerate.

Newton's Second Law

Tells us the exact magnitude of the force necessary to cause a given mass to achieve a given acceleration.

Unit of Force

The unit of force is the "kilogram-meter-per-second-squared" (kg-m/s2) or the "newton" (N).

Newton's Third Law

For every action, there is an equal and opposite reaction.

Conservation of Linear Momentum

If no external forces act on a system, then the change in the total momentum of a system is zero.

Conservation of Momentum

Momentum won't change unless an outside force is applied.

Angular Momentum

An object that is rotating will keep rotating unless a twisting force called a torque acts to make it stop.

Universal Force of Gravity

Newton's law of universal gravitation explains the force that keeps celestial bodies in their orbits.

Gravitational Constant (G)

A constant of direct proportionality that expresses the numerical relation between the masses of two objects, their separation, and the force between them.

Constant of Proportionality

A number (k) that represents the relationship between two variables, such that if one variable increases, the other variable increases by the same proportion.

Cavendish Experiment

An experiment conducted by Henry Cavendish in 1798 to measure the gravitational constant (G) using a dumbbell apparatus and the twisting force (torque) on a wire.

Weight

The force of gravity acting on an object located at a specific point, which varies depending on the location in the universe.

Mass

The amount of matter in an object, which remains constant regardless of the location in the universe.

Universal Gravitation

The law stating that there is a gravitational force between any two objects in the universe, which is proportional to their masses and inversely proportional to the square of the distance between them.

Gravitational Acceleration (g)

The acceleration due to gravity on Earth's surface, which can be calculated using Newton's universal equation for gravity and the values of the gravitational constant (G), Earth's mass (ME), and Earth's radius (RE).

Newtonian Laws

Laws of motion and the law of universal gravitation formulated by Isaac Newton, which describe the behavior of objects in motion and the force of gravity.

Clockwork Universe

The concept that the universe operates like a clock, following precise laws of motion and gravity, as proposed by Newton and his followers.

Halley's Comet

A comet whose orbit was calculated using Newtonian logic by Edmond Halley, demonstrating the applicability of Newton's laws to celestial phenomena.