1. Gravity (Act III, Scene II)
Michael Lea, Noah Chun, Amber Kim, Annalise Evans, Lauren Scoville, Luka Jovanovic

2. Concepts What Is Gravity?
Universal Gravitation and Newton’s Law of Universal Gravitation
Gravity and Distance: The Inverse Square Law
Gravitational Fields and Fields Inside a Planet
Weight and Weightlessness
Ocean Tides: Tides in Earth and the Atmosphere
Black Holes
Earth Satellites
Circular Orbits/Elliptical Orbits
Escape Speed
Common Misconceptions

3. What is Gravity?
Gravity is a natural force pulling objects together. As long as a object has mass than it means that there is a force pulling things to it and vice versa. We do not feel this force from other people because it is so small/weak, but it is the reason our universe doesn’t fall apart and the reason the moon doesn’t crash into the Earth. Gravity on Earth can be measured by approximately 9.8 m/s2. However, it varies drastically depending on where you are. The gravity of the moon is appr m/s2, whereas the gravity of the Sun is appr. 274 m/s2.

4. Universal Gravitation
In the early 20th Century, it was discovered by Albert Einstein that gravity is the warping of spacetime. This means that when you feel gravity, what you are really experiencing is this distortion of space and time.
Newton’s Law of Universal Gravitation states that every mass in the universe attracts every other mass. These masses all feel an attraction to each other, but this attraction is often too small to feel.
If you recall, we measured the attraction between Adam and Michael and the number was barely over zero Newtons. THERE IS NO SUCH THING AS ZERO GRAVITY. Even if you were very far away from Earth, you would still have a gravitational attraction to it. It would just be so small it would become insignificant.

5. Inverse Square Law Fg∝m1m2/r2
The force of gravity is proportional to the product of the masses divided by the distance between the centers of the two objects squared.
Example:
The centers of two spheres in space are 500 meters apart. Both of the spheres have masses of 100 grams.
100x100/5002
10000/250000=0.04
This would mean that the gravitational force between the two spheres are 0.04 Newtons.
Gravity gets weaker as distance gets farther or the mass becomes smaller.

6. Gravitational Fields and Fields Inside a Planet
It is a kind of force field that surrounds a massive object.
The gravitational field is equal to the free fall acceleration experienced when a force of gravity is acting on something.
Fields Inside a Planet
The gravitational field of a planet is in the inside of a planet as well as the outside.
If you started from the North pole, and fell through the earth it would take around 45 minutes to get from the north pole to the south pole.

7. Weight and Weightlessness
WEIGHT AND MASS ARE NOT THE SAME THING!!!
Weight is the force of gravity pulling you on a certain planet.
Mass is the amount of matter that makes you up. Your mass NEVER changes. You could be on Mars, jupiter, or the moon and your mass would still the same. But your weight will diffrent on each one of those planets.
The word Weightlessness is a misleading word. When you think Weightlessness you think of no gravity but that's true, it is actually just the the lack of a support force.

8. Ocean Tides: Tides in Earth and the Atmosphere
Tides are caused from the gravitational pull of both sun and moon.
Moon has about twice as much of an impact as the sun even though the sun is 175 times greater.
Moon has a greater impact because its gravitational difference is bigger meaning that it is closer to Earth.

9. Black Holes
Black holes occur when giant stars (2-3 times bigger than our sun) reach the end of their lives and collapse.
Because a star no longer has enough fuel to allow it to not collapse, it collapses.
The star keeps infinitely collapsing in on itself, compressing it.
This results in a huge amount of gravity around the black hole.
The black hole also sucks in stuff, which adds mass to it, which increases its gravitational pull, which sucks in more stuff which adds mass to it etc.
Black holes are called black holes because their gravitational pull is so strong that light cannot escape it.
Our eyes can see things when light reflects off it, but if there is not light, it is impossible to see.

10. Earth Satellites
A satellite is a moon, planet, or man-made machine that orbits a planet or a star. Earth is a satellite that orbits the Sun. Earth’s satellites include the moon, along with many other man-created machines that are put into orbit around our planet.
The reason these satellites are able to stay in orbit around Earth is because they are perpetually falling toward Earth because gravity is pulling on them, but they keep missing.
They miss Earth every time they get close to it because they are in constant motion and Newton’s First Law of Motion tells us that an object in motion will stay in motion unless acted upon by an outside force.
These satellites stay in motion around Earth in an elliptical or circular orbit, always falling toward Earth, but always missing.

11. Circular Orbits and Elliptical Orbits
Circular Orbits: A perfect circular orbit is very rare in the space world. Earth is off by 3 degrees of a perfect circular orbit. Most kids on earth recognize planets orbit as a circular, but actually, its elliptical. The only way for a planet to achieve the Circular Orbit is if it has perfect eccentricity.
Elliptical Orbits: This Orbit is what most planets follow. For an example, when a too slow or small object enters the sun's gravitational pull, it starts to orbit in a non- circular orbit because of its energy and trajectory when it enters.

12. Escape Speed
If there was no such thing as air resistance, an object would be able to leave the Earth if it was shot at a speed of 11.2 km/s or more.
However, since air resistance pushes heavily in the downward direction on an object, the escape speed needed to leave Earth’s atmosphere is actually much greater, depending on the mass of the rocket.
Since there is more gravity the nearer you are to Earth, the most speed needed is the speed necessary to lift the rocket off the ground.
An additional boost in speed in required in order to change the rocket’s path from vertical to horizontal. This boost in speed knocks the rocket into orbit.

13. How Was it Discovered and By Who?
Discoverer: Sir Isaac Newton
English mathematician and physicist
Lived from
How: When he saw an apple fall while thinking of forces of nature

14. Common Misconceptions
0 gravity exists.
There’s gravity everywhere it is just not as strong in some areas of space. The inverse square law (1/r2, where r is the distance between the objects) can never equal 0.
2. Heavier objects fall faster than lighter ones.
Gravity accelerates all objects at the same rate. The reason a flat sheet of paper falls slower than a rock is because of air resistance.
3. Gravity only pulls humans towards earth.
Gravity also pulls all objects toward each other, it's just so insignificant (because the objects are so small) that we can’t feel it.

15. Common misconceptions (Continued)
4. The further away 2 objects are, the stronger the gravitational pull.
The gravitational pull gets stronger the closer the objects are together - which is proven in the formula (Fg=Gmm/r^2) because if the r is smaller, the force of gravity will be greater.
5. The gravitational pull on an object only depends on the mass of the object.
The gravitational pull on an object also depends on the distance between the objects. Which is also shown in the formula and represented by “r.”
6. In the formula for gravity the G is referring to the gravity on earth (9.81 m/s^2)
The “G” is referring to the gravitational constant, (approximately 7 x 10^-11.) And this “G” is universally true and doesn’t just refer to how fast and object accelerated towards earth.

16. Questions
Kahoot