Gravity and the Rules of Gravity and the Rules of AttractionAttraction

Newton vs. Einstein

Mass Vs. WeightMass Vs. Weight

Mass is the amount of matter that makes up an object.Mass of an object does not change (ex. A bar of gold will always have the same mass.)

Weight is the measurement of the force of gravity on an object (gravitational pull on the mass).Ex. 1- scales measure the force that Earth exerts on the object.Ex. 2 – the weight of a bar of gold will change on different planets.

How is mass different from weight?How is mass different from weight?

mass – the amount of matter in an objectweight – the force that acts upon an object

You are weightless in free-fall!

GravityGravity – the force of attraction – the force of attraction between any 2 masses, any 2 bodies, between any 2 masses, any 2 bodies,

or any 2 particles.or any 2 particles.

Gravity exists between all objects in Gravity exists between all objects in the universethe universe

Gravitational pull is dependent on Mass- Small mass = small gravitational pull Large mass = big gravitational pull Small gravitational pull = small weight Large gravitational pull = large weight

Ex. The Moon is 1/6th the sixth the size of the Earth. So an object on the Moon would weigh 1/6th as much.

Thought QuestionThought QuestionOn the Moon: On the Moon:

A. My weight is the same, my mass is less.

B. My weight is less, my mass is the same.

C. My weight is more, my mass is the same.

D. My weight is more, my mass is less.

On the Moon…On the Moon…

A. My weight is the same, my mass is less.

B. My weight is less, my mass is the same.

C. My weight is more, my mass is the same.

D. My weight is more, my mass is less.

Gravity on EarthGravity on Earth

Acceleration due to gravity on Earth = 9.8 meters/ second2

Free falling objects increase in speed 9.8 meters per second for every second they fall. Rate of acceleration is NOT dependent on mass. Ex. A golf ball and a shot put dropped at the same time from the same height will reach Earth at the same time.For this to be true- what must we leave out?

The Acceleration of GravityThe Acceleration of Gravity

All falling objects accelerate at the same rate (not counting friction of air resistance).

On Earth, g ≈ 9.8 m/s2: speed increases 9.8 m/s with each second of falling.

One Exception for Gravity on One Exception for Gravity on Earth……Earth……

Earth has an atmosphere- so, Gravity is:

NOT independent of air resistance

Air Resistance slows down acceleration

In vacuum, all objects fall at the same rate.

Without a vacuum- objects fall at rates depending on their surface areas.

Acceleration of Gravity of an Acceleration of Gravity of an object on Earth is independent object on Earth is independent

of…of…1. The mass of the object

2. Velocity of the object parallel to the ground (I.e. horizontal velocity)

3. Then this means…

If an object …If an object …

..is traveling at a certain velocity parallel to the Earth’s surface,it will fall to the Earth at the same rate as a stationary object (falling straight to Earth) dropped at the same height.

Ex. Simultaneously shoot a bullet from a gun and drop a bullet straight from the same height- both bullets will hit at the same time.

The Effect of Gravity on Earth The Effect of Gravity on Earth

Keeps our Earth’s atmosphere, oceans, and inhabitants from drifting into space

Pulls rain into rivers and eventually into the oceans

Effects the way our muscles and bones develop and function. (ie. bench pressing, dunking a basketball.)

Realized the same physical laws that operate on Earth also operate in the heavens one universe

Discovered laws of motion and gravity

Much more: experiments with light; first reflecting telescope, electromagnetic spectrum, calculus…

Is most famous for his work- “Principia” which was two years of thought and scribbling, but was only a recounting of what he could remember.

How did Newton change our view of the Universe?

Sir Isaac Newton (1642-1727)

Newton was a neat guy….Newton was a neat guy…. Described as “odd, brilliant beyond measure, solitary,

joyless, prickly to the point of paranoia, famously distracted.”

Capable of riveting strangeness Once inserted a “bodkin” – a long needle used for

sewing leather- into his eye socket and rubbed it around “betwixt my eye and the bone as near to the backside of my eye as I could” just to see what would happen.

A hair sample analyzed in the 1970s found a high level of mercury – 40 times the natural level found for most people.

Newton: Ideas About GravityNewton: Ideas About Gravity

Gravity is apparent everywhere on Earth from the mountains to the valleys

He wondered – Does gravity…

Extend to the Moon? Account for Earth and

Moon movement? Motions of other

planets?

Variables

Two variables can change the force of gravity:

1. The mass of the objects

2. The distance between the objects

Universal Law of GravitationUniversal Law of Gravitation• Every mass attracts other mass through the

force of gravity. Anything with a mass has its own gravity, although it may be very small *: note that gravity obeys the inverse square rule

Breaking down the equation…

Fg = force of gravity

G = gravitational constant = 6.67 x 10-11 N.m2/kg2

M1 = mass of the first object

M2 = mass of the second object

d = distance between the centers of each object

This means that:This means that:

As objects get farther apart, the effect of gravity drops.Ex. An object 1 km from Earth is pulled much more strongly than an object 3km away. This drop is an “inverse proportion”

Questions to consider!Questions to consider!

1. Why do tides occur in the lakes and oceans on Earth?

2. How do planets in our solar system stay in orbit?

3. How does the Sun’s force travel through so much empty space?

4. What would happen if a person stepped out into space and opened a package of Skittles? M&Ms?

Einstein and Relativity That Einstein and Relativity That Anyone Can UnderstandAnyone Can Understand

First things first – to understand where Al was coming from, we must remember the following:

The speed of light is the universal speed limit (299,792.458 km/ sec.)

The flow of time is dependent upon the state of the clock

Space and time are interconnected. (adding a fourth dimension)

The speed of light in empty space can not be reached or exceeded by any massive object in the universe.

Einstein’s New Theory of Einstein’s New Theory of GravityGravity

Einstein felt that Newton’s view of gravity worked well on Earth, but not so well in space.Einstein felt that gravity should be described as a field in space rather than a strange property of matter.Any object that has mass must have gravity.Gravity is the result of the interaction between matter and space – between the Earth and the space immediately surrounding the Earth.

Spacetime and Einstein's Spacetime and Einstein's GravityGravity

The mass of an object creates a “warp” or “distortion” of space time.

The greater the mass, the greater the distortion.

The size of the distortion determines the motion of the objects around it.

Gravity is Curved SpaceGravity is Curved Space

For planets orbiting the Sun – they are effected by the largest warp in space time.

The Sun is the most massive, so it has the most gravity.

This ‘gravity’ tells that planets how to move.

If Spacetime was a If Spacetime was a TrampolineTrampoline

Picture Spacetime as a trampoline holding 100 people of equal weight.

If everyone has their own space, the trampoline should remain evenly distributed. (with no large lumps.)

What would happen if everyone walked into the middle, creating a large warp in spacetime?

As the people move towards the As the people move towards the center- the “warp” grows larger. center- the “warp” grows larger.

Eventually, even the furthest person Eventually, even the furthest person is effected by the warped spacetimeis effected by the warped spacetime

Gravity, Escape Velocity, and Gravity, Escape Velocity, and Black HolesBlack Holes

Now that we understand a little more about gravity: ponder these questions-

How fast would an object have to go to escape the gravity of Earth?

Is it possible to have an object so massive that the escape velocity is beyond the speed of light?

What about a “Theory of Everything?”