Lecture3 part1 video

Summary

In this lecture, the focus is on gravity and motion, highlighting Galileo's and Newton's contributions. Galileo introduced the concept of inertia, challenging Greek beliefs that motion naturally ceased. Newton built upon this, formulating the first law of motion, which states that an object will remain at rest or in uniform motion unless acted upon by an external force. He also identified gravity as the force causing planets to move in elliptical orbits, explaining the structure of the universe. The lecture also touches on the idea of orbits as a state of constant freefall towards Earth, illustrating why astronauts appear weightless in space.

Takeaways

• 🌟 Galileo's observations of the night sky and his studies on motion led to the concept of gravity.
• 🏃‍♂️ Inertia, as introduced by Galileo, states that a body at rest stays at rest, and a body in motion stays in motion unless acted upon by a force.
• ❌ Galileo's concept of inertia contradicted the ancient Greek belief that motion naturally comes to rest.
• 🔧 Friction is identified as a force that can slow down motion, which was not fully understood in Galileo's time but later incorporated into Newton's laws.
• 🎓 Isaac Newton, building on Galileo's work, formulated the first law of motion, which describes the behavior of objects under the influence of forces.
• 📘 Newton's first law of motion states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.
• 🌌 Newton recognized that the force causing objects to move in elliptical orbits, which is not a straight line, is gravity.
• 🌐 Gravity is the fundamental force that shapes the universe, holding galaxies, solar systems, and other celestial bodies together.
• 🚀 Newton's laws of motion and his equations for gravity explain why planets move in elliptical orbits and the nature of orbits in general.
• 🧭 Newton's work also explains the concept of an orbit as a state of constant falling towards the Earth while moving at sufficient velocity to not hit the surface.
• 🔭 Newton's contributions to physics include the invention of calculus, the development of the laws of motion, and advancements in optics and telescope design.

Q & A

What significant concept did Galileo observe that was foundational to the idea of gravity?

Galileo observed the concept of inertia, which states that a body at rest tends to remain at rest, and a body in motion tends to remain in motion unless acted upon by an external force.

How did Galileo's observations of motion contradict the beliefs of Greek physicists?

Greek physicists believed that objects in motion tended to come to rest, while Galileo demonstrated that objects continue in motion unless a force acts upon them to change their state.

What was the significance of the year Galileo died in the context of scientific history?

The year Galileo died, 1642, is significant because it was the same year Isaac Newton was born, marking the transition from Galileo's work on motion and inertia to Newton's advancements in physics.

What did Newton's first law of motion state, and how did it relate to the concept of inertia?

Newton's first law of motion states that a body continues in a state of rest or uniform motion in a straight line unless acted upon by an external force. This law is an extension of Galileo's concept of inertia.

How did Newton's understanding of gravity explain the motion of celestial bodies?

Newton realized that gravity is the force that causes planets to move in curved orbits rather than in straight lines, as inertia would otherwise dictate.

What is the relationship between gravity and the structure of the universe as described in the script?

Gravity is the fundamental force that holds the universe together, forming structures like galaxies, solar systems, and clusters of galaxies.

What is an orbit, as explained in the context of gravity and motion?

An orbit is a path where one object goes around another due to gravity. Objects in orbit are constantly falling towards the center of the Earth but moving forward fast enough that they do not hit the Earth.

Why do astronauts appear weightless while in orbit, according to the script?

Astronauts appear weightless because they are in freefall, experiencing gravity but falling towards the Earth in a way that they continuously orbit without touching the surface.

What did Newton's work on gravity allow him to explain about the motion of the moon?

Newton's work on gravity allowed him to explain the moon's motion by demonstrating that the same force that causes objects to fall on Earth also influences the moon's orbit around the Earth.

What are the implications of Newton's laws of motion for our understanding of physics today?

Newton's laws of motion are still in use today and form the basis for our understanding of classical mechanics, including the behavior of objects and celestial bodies under the influence of forces.

Outlines

00:00

🌌 Introduction to Gravity and Motion

This segment introduces the topic of gravity and motion, highlighting the historical context of Galileo's observations and the concept of inertia. Galileo's work contradicted the Greek physicists' belief that motion naturally ceased, instead showing that objects in motion tend to stay in motion unless acted upon by a force, such as friction. The lecture sets the stage for discussing the laws of motion and the pivotal role of gravity in the universe.

05:02

📚 Newton's Laws of Motion and the Role of Gravity

This paragraph delves into Newton's first law of motion, which builds upon Galileo's concept of inertia, stating that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. The discussion then transitions to the concept of orbits, explaining how planets move in elliptical paths due to the force of gravity. Newton's realization that gravity is the force that causes celestial bodies to move in curved orbits is a fundamental principle that shapes our understanding of the universe's structure.

10:03

🚀 Understanding Orbits and the Experience of Weightlessness

The final paragraph explores the concept of orbits, explaining that objects in orbit are in a state of continuous freefall around the Earth, never actually hitting it due to their velocity. This discussion clarifies the misconception of weightlessness in space, emphasizing that astronauts experience gravity but in a state of freefall, which gives the appearance of weightlessness. The lecture concludes with a teaser for upcoming topics, including further exploration of Newton's laws of motion.

Keywords

💡Gravity

Gravity is the force that attracts two objects with mass towards each other. In the context of the video, gravity is the central force that governs the motion of celestial bodies, including the Earth and the planets. It is the reason why objects fall towards the Earth and why planets orbit the Sun in elliptical paths. The video explains that gravity is a universal force that holds the universe together, forming structures like galaxies and solar systems.

💡Motion

Motion refers to the movement or change in position of an object. The video discusses how the study of motion led to the concept of gravity. It explains that objects in motion tend to stay in motion, and objects at rest tend to stay at rest, a principle that was later formalized by Newton as his first law of motion.

💡Inertia

Inertia is the resistance of any physical object to a change in its state of motion or rest unless acted upon by an external force. Galileo's observations about inertia contradicted the Greek physicists' beliefs and laid the groundwork for Newton's first law of motion. In the video, inertia is used to explain why objects continue in their state of rest or uniform motion unless acted upon by a force.

💡Galileo

Galileo Galilei was an Italian astronomer, physicist, and engineer who is often referred to as the 'father of modern science'. In the video, Galileo is credited with establishing the concept of inertia and making significant observations about motion and celestial bodies, which were foundational to the development of the theory of gravity.

💡Newton

Sir Isaac Newton was an English mathematician, physicist, and astronomer who is best known for his laws of motion and universal law of gravitation. The video discusses how Newton built upon Galileo's work to codify the laws of motion and to articulate the mathematical principles of gravity, which are essential for understanding the structure of the universe.

💡First Law of Motion

Newton's first law of motion, also known as the law of inertia, 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 a net external force. The video explains how this law challenges the earlier Greek belief that motion naturally comes to rest and instead shows that motion continues unless a force, like friction, acts to stop it.

💡Friction

Friction is a force that opposes the relative motion or tendency of such motion of two surfaces in contact. In the video, friction is explained as a force that can slow down an object in motion, illustrating how it is an external force that can change the state of motion of an object, as described by Newton's first law of motion.

💡Orbit

An orbit is the curved path of an object moving around another object, typically under the influence of gravity. The video uses the concept of orbit to explain how planets move around the Sun and how gravity is the force that causes this curved motion. It also describes how objects in orbit are in a state of freefall, always falling towards the Earth but moving sideways fast enough to miss it.

💡Freefall

Freefall is the state in which an object moves under the influence of gravity alone, without any other forces acting upon it. The video describes how astronauts in orbit are in a state of freefall, experiencing weightlessness because they are falling towards the Earth but moving horizontally at a speed that keeps them in orbit.

💡Weightlessness

Weightlessness is the condition in which an object or person experiences no force of gravity. In the video, it is explained that astronauts in orbit appear weightless because they are in freefall, constantly falling towards the Earth but moving horizontally at a speed that keeps them from hitting the surface, creating the illusion of weightlessness.

Highlights

Galileo's observations of the night sky and his studies on motion led to the concept of gravity.

Galileo established the idea of inertia, contradicting Greek physicists who believed motion tended to stop.

Galileo demonstrated that forces, like friction, are what cause objects to stop moving, not a natural tendency to rest.

Isaac Newton, born the year Galileo died, is considered a genius and contributed significantly to physics and optics.

Newton developed calculus, laws of motion, and a new type of telescope during the plague years in London.

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

Balanced forces result in no net force, causing an object to remain at rest or in uniform motion.

Velocity is defined as the speed and direction of an object's movement.

Galileo and Kepler showed that orbits are elliptical, not straight lines, contradicting the idea of uniform straight-line motion.

Newton identified gravity as the force that causes planets to move in elliptical orbits.

Gravity is the fundamental force that structures the universe, holding galaxies and solar systems together.

Newton's equations for gravity and motion explained the moon's motion and the concept of orbits.

Orbits occur because objects in orbit are constantly falling towards the Earth but moving fast enough to miss it.

Astronauts in the space station experience weightlessness because they are in freefall, not because of zero gravity.

The concept of weightlessness can be experienced in an elevator freefall, though it is not recommended.

Upcoming lectures will cover Newton's other laws of motion and their practical applications.

Transcripts

okay class welcome to part 1 of lecture

3 now in this class were to be talking

about gravity and motion now last time

we left off leading up to or through the

observations of the Renaissance

Europeans and the word Galileo now

Galileo observed lots of things in the

night sky but he also studied motion and

motion the study of motion turns out to

lead us to the idea of gravity itself

and this comes through Galileo and then

new so inertia now Galileo

working in southern Italy established

the idea of inertia now what this means

is that if a body now by me my body is

any kind of object that has mass the

body is at rest it tends to remain at

rest now if that means if then you have

a ball and just sitting on the ground

it's gonna keep doing that it's gonna

remain at rest however a body in motion

tends to remain in motion and this idea

of Galileo is actually directly

contradicted the ideas of the Greek the

Greek physicists we call them physicists

today they believe that objects in

motion tended to come to rest now if

you're actually watching things in

nature this idea actually kind of makes

sense the idea of you you push something

it moves for a little bit but then it

slides to a stop and the Greeks believed

that all motion eventually ended at rest

but Galileo demonstrated that in fact

what's going on here the reason why

certain things come to a stop is because

of forces now he wouldn't I call them

forces but Newton would codify this idea

and in particular friction

so if you start something moving

friction will slow it down but that is

something that's making it slow down

without any force things will continue

in motion

and this is actually so Galileo dies the

same year Isaac Newton is born Isaac

Newton well he is considered and in all

I see we considered Isaac Newton was a

genius and Isaac Newton during the

plague years in London went back to his

estate and over a couple of years came

up with lots of stuff he invented

calculus he invented our ideas of how

well modern physics you know laws of

motion he does work on optics he invents

a new kind of telescope the mirrored

telescope which we'll talk about later

and during this time Newton takes

Galileo's ideas and codifies the first

law of motion and that says that a body

continues in a state of rest or uniform

motion in a straight line unless made

change that state by forces acting on it

so an object at rest something it's not

moving will continue not to move unless

some forces apply so unless you push it

if an object is moving it will continue

to move in a straight line unless some

kind of force is applied change that

velocity now there are various ways to

think about this okay balanced forces

first of all if an object is sitting on

a table and one person is pushing this a

box one person is pushing on it another

person is pushing on it and they are

pushing with exactly the same amount of

force such that US forces balance they

equal out

well that's zero force and if zero force

is being applied to the box it doesn't

move but if one person like goes away

and stops pushing well now you have a

force in one direction and the box is

going to move gave velocity velocity is

a speed of an object and the direction

it's moving now this idea the idea that

objects will move in a straight line a

straight line unless some kind of force

interacts with them to make them move in

a not straight line or to make them move

at all well Galileo investigated this a

Kepler and Galileo were able to

demonstrate that in fact orbits are

elliptical that's not a straight line

the Galileo was not quite able to codify

this into an a law but Newton realized

that hey wait a second my first law says

that objects will move in a straight

line without changing their velocity

unless some force is applied but if you

look at orbits well sure enough orbits

they're definitely not straight lines

right there ellipses they curve and if

an object is not moving in a straight

line if it's curving well there has to

be a force and in particular Newton and

called this force gravity and realize

it's the same kind of force that makes

things here on the earth fall that same

force that makes things here on the

earth fall to the ground can also

explain why planets move in a elliptical

orbit a gravity is the force that makes

planets move in curved orbits so

normally a planet would want or because

of inertia

should go off in a straight line but

gravity pulls it so that it goes in a

curved orbit which is an ellipse and

gravity as it turns out is the

fundamental force that defines the

structure of our universe it's why the

universe looks the way it does is why we

have things like clusters of galaxies

and galaxies themselves is why we have

solar systems it's what holds the

universe together the parts of the

universe that make up things like

galaxies so let's hold them together

it's hugely important we're talk a lot

about it in this class how gravity holds

things together it pulls things together

it makes things like planets and stars

form it is why we have galaxies etc and

now while Newton was not the first

person to suggest the idea that there

was some kind of force holding things

together Newton did actually come up

with an equation so the properties for

gravity and he came out with equations

for motion so how gravity influenced

motion and he was able to explain why

the moon's motion moved or why the moon

moved the way it did he also is able to

explain based on this idea of a force of

gravity why a while you have orbits what

exactly an orbit is because this is

actually a kind of an important idea

think about what an orbit means in orbit

is one thing going around another but

why well it's because of gravity so

think about this let's say you have a

cannon and you fire the cannon off with

a relatively small amount of gunpowder

and the ball goes out and it falls down

here now if you put more gunpowder in

it's gonna go further

and further and even further the more

and more gunpowder you put into it but

right now what we're magining is a

ground that's flat wait to remember the

earth is not flat the earth is round and

so the ball while you know you shoot it

out further and further faster and

faster it goes further and further it's

always curving back down towards the

ground well remember the earth is round

so she'd the ball out it curves towards

the ground

well shooter that with more and more

force and it goes further and further

before it hits the ground you shoot it

with enough force it should while always

falling towards the earth right it's

always falling towards the earth but it

will go all the way around the earth and

never actually hit it

that's an orbit that's what an orbit is

things that are in orbit are always

falling towards the center of the earth

they're just moving away from the center

of the earth in enough velocity such

that they never actually hit the earth

this is why astronauts and the space

station it's why they seem they look

like they're weightless right they float

around they are in fact weightless what

they are not experiencing is zero

gravity

they're definitely experiencing gravity

it's why they're in orbit around the

Earth but they are falling towards the

Earth while always going around the

earth fast enough they never actually

hit it which means they're in freefall

they are in freefall not zero gravity

they are definitely experiencing gravity

but they're falling towards the earth in

freefall which is why they appeared to

be weightless okay if you want to

experience what astronauts experience in

the space station well you

could do that I don't recommend this but

you could get into an elevator at the

very top of a very tall building and

then cut the cord okay as the elevator

falls towards the ground

well you in the elevator for a little

bit of time you are going to experience

weightlessness it won't end well don't

do that but that is what's happening

with astronauts all right now in the

next couple of parts of this lecture

we're going to talk about the other laws

of motion that Newton came up with

during this time that are still in use

today so stay tuned