Newtonian physics and relativity

Summary

This video explores the foundational concepts of Newtonian physics, including Newton's three laws of motion and the law of universal gravitation, which laid the groundwork for understanding motion and forces. It contrasts these with Einstein's theories of relativity, which introduced the idea that time and space are relative and could be affected by motion and gravity. The video highlights the differences between Newton's absolute concepts of space and time and the relativistic view where they are intertwined, leading to a deeper understanding of phenomena like gravity as a curvature of space-time. It also touches on the unresolved questions and the ongoing quest for a unified theory that reconciles quantum mechanics with general relativity.

Takeaways

• 🎉 **Newton's Birthday**: January 4th marks the birthday of Sir Isaac Newton, who introduced foundational laws of physics.
• 📚 **Newtonian Physics**: Newton's laws, including the three laws of motion and the law of universal gravitation, form the basis of classical mechanics.
• 🔄 **Inertia and Motion**: Newton's first law explains that an object will remain at rest or in uniform motion unless acted upon by an external force.
• ⚖️ **Force and Acceleration**: Newton's second law (F=ma) links force, mass, and acceleration, describing how forces affect the motion of objects.
• 🔄 **Action and Reaction**: The third law states that every action has an equal and opposite reaction, a fundamental principle in dynamics.
• 🌐 **Universal Gravitation**: Newton's law of universal gravitation describes the gravitational attraction between masses and the concept of gravity.
• 🌌 **Evolution of Physics**: Physics has evolved beyond Newtonian mechanics with the advent of theories like general relativity, which offer deeper insights into the universe.
• 🚀 **Special Relativity**: Einstein's special relativity, introduced in 1905, asserts that the laws of physics are the same in all inertial frames and that the speed of light is constant.
• 🌀 **General Relativity**: Einstein's 1915 theory of general relativity posits that gravity arises from the curvature of space-time by mass and energy.
• 🌠 **Orbits and Predictions**: General relativity provided a more accurate explanation for the orbit of Mercury, including the precession of its perihelion, which Newtonian mechanics could not fully account for.

Q & A

What significant contribution did Isaac Newton make to physics?

Isaac Newton formulated Newtonian physics, which includes the three laws of motion and the law of universal gravitation, providing some of the earliest comprehensive descriptions of how objects move and how the physical world operates.

What is Newton's first law of motion, also known as the law of inertia?

Newton's first law states that a body at rest or in motion will continue to remain at rest or in motion unless acted upon by an external force.

How is the force acting on an object described by Newton's second law?

Newton's second law describes the force acting on an object as the product of its mass and acceleration, mathematically expressed as F = ma.

What does Newton's third law of motion entail?

Newton's third law states that for every action, there is an equal and opposite reaction, meaning that forces between two bodies are equal in magnitude and opposite in direction.

What is the law of universal gravitation as described by Newton?

The law of universal gravitation states that the force of gravity between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

What is an inertial frame of reference in the context of Newtonian physics?

An inertial frame of reference is a frame where either there is no motion or the motion is at a constant velocity with no acceleration. Newtonian physics assumes that all observers in different inertial frames will see the same physical phenomena.

How did James Clerk Maxwell's equations of electromagnetism challenge the principles of Newtonian physics?

Maxwell's equations of electromagnetism showed that the form of these equations changed depending on the observer's inertial frame of reference, which contradicted the absolute nature of space and time in Newtonian physics.

What was the significance of the Lorentz transformation in the development of physics?

The Lorentz transformation demonstrated that time and length are not absolute but change depending on the observer's inertial frame, which was a departure from Newtonian physics and laid the groundwork for the theory of relativity.

What was the main postulate of Einstein's special relativity?

Special relativity postulates that the laws of physics are the same in all inertial frames and that the speed of light in a vacuum is constant for all observers, regardless of the motion of the light source or observer.

How does Einstein's general relativity differ from Newtonian physics in explaining gravity?

General relativity posits that gravity is not a force but rather a consequence of the motion of masses through curved space-time, caused by the presence of mass, which contrasts with Newtonian physics where gravity is viewed as a force acting at a distance.

What was one of the major predictions of general relativity that confirmed its validity?

One of the major predictions of general relativity that confirmed its validity was the observation that the orbit of Mercury's perihelion precesses, which could not be fully explained by Newtonian physics but was accurately predicted by general relativity.

Outlines

00:00

📚 Newtonian Physics and Its Evolution

This paragraph introduces the historical significance of Isaac Newton's contributions to physics, specifically his laws that laid the foundation for understanding motion and gravity. Newton's laws of motion and the law of universal gravitation are explained, emphasizing their universality across inertial frames of reference. The paragraph also touches on the concept of inertial frames and how they relate to our perception of motion. It sets the stage for a discussion on the evolution of physics, leading to the theories of relativity.

05:02

🌌 From Newton to Einstein: The Shift in Understanding Gravity

The second paragraph delves into the transition from Newtonian physics to Einstein's theory of relativity. It highlights the discrepancies between the two theories, particularly in the context of high velocities and strong gravitational fields. The paragraph explains how Einstein's special relativity, which posits that the laws of physics are consistent across all inertial frames and that the speed of light is constant, challenged the absolute nature of space and time in Newtonian physics. It also introduces general relativity, which describes gravity as a curvature of space-time caused by mass. The paragraph concludes by discussing the implications of these theories on our understanding of celestial bodies, such as the orbit of Mercury, and acknowledges the ongoing quest to answer questions that even general relativity cannot yet fully explain.

Keywords

💡Newtonian Physics

Newtonian Physics refers to the classical framework of mechanics that was formulated by Sir Isaac Newton in the 17th century. It includes Newton's three laws of motion and the law of universal gravitation. These laws describe the motion of objects and the forces that affect them. In the video, Newtonian Physics is discussed as the foundational understanding of how the physical world works, with examples like the law of inertia and the concept of an equal and opposite reaction.

💡Law of Inertia

The law of inertia, also known as Newton's first law, states that an object at rest will stay at rest, and an object in motion will stay in motion with a constant velocity, unless acted upon by an external force. This law is fundamental to understanding motion and is a cornerstone of Newtonian Physics. In the video, it's mentioned as one of the basic laws that govern the behavior of objects in our everyday world.

💡Law of Universal Gravitation

Newton's law of universal gravitation is a principle that describes the gravitational attraction between masses. It states that every point mass attracts every other point mass by a force acting along the line intersecting both points. The video explains this law as a key component of Newtonian mechanics, which helps to explain phenomena such as planetary orbits and the falling of objects.

💡Inertial Frame of Reference

An inertial frame of reference is a theoretical frame of reference in which an object either remains at rest or moves at a constant velocity unless acted upon by an external force. This concept is crucial for understanding relative motion and is used in Newtonian Physics to describe the motion of objects as observed from different perspectives. The video script uses the example of a person walking and a train moving to illustrate how inertial frames help us describe motion.

💡Electromagnetism

Electromagnetism is a branch of physics that deals with the study of the electromagnetic force, one of the four fundamental forces of nature. It is described by James Clerk Maxwell's equations and encompasses electricity, magnetism, and light. In the video, electromagnetism is mentioned as a field that was initially inconsistent with the principles of Newtonian Physics because its equations changed depending on the observer's inertial frame.

💡Lorentz Transformation

The Lorentz transformation is a mathematical transformation that describes how measurements of space and time are related between two inertial frames moving relative to each other. It was introduced by Hendrik Lorentz and is fundamental to the theory of special relativity. The video explains that the Lorentz transformation showed that time and length are not absolute but change depending on the observer's frame of reference, which challenged the Newtonian concept of absolute space and time.

💡Special Relativity

Special relativity is a theory of physics that was introduced by Albert Einstein in 1905. It deals with the physics of objects moving at speeds close to the speed of light and posits that the laws of physics are the same in all inertial frames and that the speed of light in a vacuum is constant for all observers. The video script mentions special relativity as a theory that challenged and expanded upon Newtonian Physics by introducing the idea that space and time are not absolute but relative.

💡General Relativity

General relativity is a theory of gravitation proposed by Albert Einstein in 1915. It describes gravity not as a force but as a curvature of spacetime caused by mass and energy. This theory has been fundamental in understanding phenomena that Newtonian Physics could not explain, such as the orbit of Mercury. The video script discusses general relativity as a major advancement in physics that provides a different perspective on gravity and the structure of the universe.

💡Spacetime

Spacetime is a concept in physics that combines the three dimensions of space with the one dimension of time into a single four-dimensional continuum. It is a fundamental concept in Einstein's theories of relativity, where it is proposed that space and time are interwoven into a fabric that is affected by mass and energy. The video explains that in general relativity, gravity is the result of motion through this curved spacetime.

💡Singularity

In the context of general relativity, a singularity is a point in spacetime where the laws of physics as we understand them break down. It is often associated with black holes, where gravitational forces are so strong that they cause spacetime to curve infinitely. The video script mentions singularities as areas where even the laws of relativity do not apply, indicating the limits of our current understanding of the universe.

Highlights

Isaac Newton's birthday on January 4th, 1643, marks the birth of Newtonian physics.

Newtonian physics introduced fundamental laws describing the motion of objects in the world around us.

Newton's First Law of Inertia states that a body will remain at rest or in motion unless acted upon by an external force.

Newton's Second Law defines force as the product of an object's mass and acceleration (F = ma).

The Third Law of Motion asserts that every action has an equal and opposite reaction.

Newton's Law of Universal Gravitation describes the gravitational force between two masses.

Newtonian mechanics assumes that all observers in different inertial frames will observe the same physical phenomena.

An inertial frame of reference is used to describe relative motion without acceleration.

James Clerk Maxwell's equations of electromagnetism showed that the form of equations can change depending on the observer's frame.

Henrik Lorentz's transformation allowed for the preservation of the form of Maxwell's equations across different inertial frames.

Lorentz transformation revealed that time and length are not absolute but change with the observer's frame of reference.

Einstein's Special Relativity, introduced in 1905, postulated that the laws of physics are absolute in all inertial frames and that the speed of light is constant.

General Relativity, proposed by Einstein in 1915, suggests that gravity is the result of motion in a curved space-time caused by mass.

Newtonian physics and relativity do not contradict but are applicable in different contexts, with relativity taking precedence at high velocities.

General Relativity provided explanations for phenomena like the orbit of Mercury, which Newtonian physics could not fully account for.

Both Newtonian physics and general relativity have limitations, such as the breakdown of known laws at singularities within black holes.

Transcripts

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january the 4th is isaac newton's

birthday

from the year 1643 and newton gave us

the gift of newtonian physics

which were some of the earliest laws

that described

how the world around us worked and how

objects around us

moved physics has of course evolved

since and today we have the wonderful

theory of general relativity from which

we're still

learning new things about our universe

in this video

let's take a very basic simplified look

at the laws newton put forth

where and why they don't apply how

relativity helps

solve some questions and where newton

and einstein

differed in their theories i'm sandhya

ramesh and this is pure science

in the 17th century newton came up with

a set of rules and equations

that describe the physical world around

us

we all know these if we've studied

newton's three laws of motion in school

the first law the law of inertia states

that a body at rest

or in motion will continue to remain at

rest or in motion

unless an external force acts upon it

the second law states that the force

acting on an object

is the product of its mass and

acceleration f is equal to m a

the third law is that for every action

there is an equal and opposite reaction

newton also gave us the famous law of

universal gravitation

the force of gravity between two objects

is directly proportional to the product

of their masses

and inversely proportional to the square

of distance between them

all these equations and laws are a part

of newtonian mechanics or

classical mechanics these laws and

equations

came with an important property which is

that

all observers no matter where they're

situated and whether they're moving

that is regardless of which inertial

frame

they are in they would see the same

things

around them happening in the same way

these laws were considered to be

universal

an inertial frame of reference is our

way of

understanding and describing relative

motion

say a person is walking in front of me

from left to right

i am stationary so the person appears to

move to me

and is of course in fact moving however

both of us are on the surface of the

earth and the earth

is revolving around the sun moving

through space

but for the purposes of this observation

we assume that the earth is stationary

so

earth is our inertial frame of reference

we've seen more examples in our school

textbooks

if a person traveling in a train throws

a ball

up and the ball falls down it will fall

straight down for the person inside the

train

but if i'm standing on a road and seeing

the train pass

by i would see the same ball taking a

path that is

parabolic for the person inside the

train

the train is the inertial frame of

reference and the ball

is moving relative to the train inertial

frames

are in inertia so either in motion with

the same velocity

or at rest they are not accelerating

then in the 19th century james clerk

maxwell came up with a set of equations

when he was studying electricity

magnetism and light

this was combined to form what we know

as electromagnetism today

but a funny thing about these equations

where that the form of these equations

changed depending

on the observer's inertial frame of

reference

then came along henrik lorenz in the

early 20th century

who with what we know as lauren's

transformation

which we're not going to go into was

able to show

that these equations could have their

form preserved

even when the inertial frame changes the

lorenz transformation

transformation of inertial frames was

different from the

standard transformation of inertial

frames that was being applied for

newtonian physics

in newtonian physics length and time

are constant they are absolute and don't

change

so an object of a certain length in one

frame

is of the same length in a different

frame as well

and this is the same with time it passes

the same way

in all frames of reference but

the lorentz transformation showed that

time and

length actually do change depending on

which frame of reference you're

in and this made who else but

einstein think he wanted to understand

if time and length

by length space were invariable

so he first came up with special

relativity in 1905.

this theory postulated that the laws of

physics are absolute in

all inertial frames of reference and

that the speed of light in vacuum is the

same for all observers

irrespective of whether the observer or

the source of light is in motion

but without going into too much details

here

einstein basically realized that gravity

changed everything

this was because gravity was basically

acceleration for earth we know the value

of

small g 9.8 meters per second square

which means that

any body that is falling towards the

surface of earth

is accelerating or increasing in speed

at the rate of 9.8 meters per second

every second the falling object would

experience the same force if it's inside

a vehicle

that is accelerating at this rate or at

one g

and when acceleration or gravity was

factored into these equations even basic

geometry changes

this led einstein to realize that

gravity was actually the result of

motion not just through space but also

through time

all of this is of course extreme

simplification of all the work that went

into it

but einstein then eventually put forth

his theory

of general relativity in 1915

with the premise that mass distorts and

bends

space-time causing it to curve and

gravity

is essentially the result of motion in

this curved space time

now where do newtonian physics and

relativity differ technically they don't

contradict each other but when energies

or velocities are approaching the speed

of light

relativity applies instead of newtonian

physics because of space-time curvature

in newtonian physics there is no

difference in space and time

no matter where you're located or how

fast you're moving

in fact theoretically you can travel as

fast as you want if you have

enough force relativity however states

that nothing can travel faster than the

speed of light

general relativity changed the field of

physics completely

it entirely transformed how we

understood the world around us

and the universe around us it offered

explanations for many lingering

questions

in physics and in astronomy such as

very famously the example of the orbit

of mercury with newton's laws

in a two body system such as the sun and

mercury

where one object is orbiting around

another

the orbit will be in the form of an

ellipse with

the bigger mass at one of the two focal

points

this is true we do know that pretty much

all orbits are

elliptical to varying degrees so it was

thought

that in this classical elliptical orbit

according to newtonian physics that

mercury was in

the perihelion or the closest point to

the sun in the orbit

was fixed with every orbit and the data

and observations

fit this theory determining the orbit of

mercury was one of the biggest

tests for general relativity but of

course

just like newtonian physics couldn't

answer everything that we observe

around us general relativity doesn't

either

black holes are predicted by general

relativity

and singularities where all known laws

of physics break down

are allowed in general relativity but

at the point of a singularity inside a

black hole

the laws of relativity also break down

similarly we have many other questions

from general relativity that are still

unanswered

which hopefully in the near or far

future

we are able to answer because time flows

in only one direction