PhET/C3/Gravity-and-Solar-system/English-timed

Time	Narration
00:01	Welcome to this tutorial on Gravity and Solar System.
00:06	In this tutorial, we will demonstrate Gravity and Orbits and My Solar System, PhET simulations.
00:16	Here I am using- Ubuntu Linux OS version 14.04
00:23	Java version 1.7.0 and
00:27	Firefox Web Browser version 53.02.2
00:34	To follow this tutorial, learner should be familiar with topics in high-school science.
00:42	Using these simulations, we will - 1. Describe the relation between Sun, Earth, Moon and satellite.
00:51	2. Study the effect of mass and distance on gravitational force.
00:56	3. Explain how gravity controls the motion of our solar system.
01:02	4. Identify the variables that affect the strength of gravity.
01:08	5. And, determine the gravitational force.
01:12	In our solar system, all the celestial objects revolve around the Sun.
01:18	These objects are planets, moons, comets, asteroids, meteors and meteorites.
01:27	There exists a force of attraction between the Sun and the celestial objects.
01:34	This force of attraction is gravitational force.
01:39	Let us begin the demonstration.
01:43	Use the given link to download the simulation.
01:48	I have already downloaded Gravity and Orbits simulation to my Downloads folder.
01:55	To open the simulation, right click on gravity-and-orbits_en.html file.
02:01	Select Open With Firefox Web Browser option.
02:06	Simulation opens in the browser.
02:10	This is the interface of Gravity and Orbits simulation.
02:16	The interface has two screens- Model, To Scale.
02:22	Let us begin our demonstration with Model screen.
02:26	Click on Model screen to open it.
02:29	On the right side of the screen you can see a box.
02:34	It has four solar system like models.
02:38	Next to models, there is a gray colored Reset button.
02:43	This button sets the solar system to its default state.
02:48	We can select Gravity, using on and off radio buttons.
02:54	Below Gravity, we have check-boxes for- Gravity Force, Velocity, Path and Grid .
03:03	Click on all the check-boxes.
03:06	Below this box, we have another box. It consists of sliders to change the mass of Star and Planet.
03:15	Bottom of the screen, we have Fast Forward, Normal and Slow motion radio buttons to change the animation speed.
03:25	By default, Normal speed is selected.
03:29	Also, there are Rewind, Play/Pause and Step buttons,
03:35	Clear button to reset the Earth Days count,
03:39	Reset button to reset the simulation.
03:43	By default, Sun and Earth system is selected.
03:48	Now click on Play button.
03:51	Notice that Earth revolves around the sun along a circular path.
03:57	This circular motion is due to centripetal force.
04:02	Centripetal force causes change in acceleration and keeps the body moving along the circular path.
04:11	This force acts towards the center.
04:15	This circular path is its orbit.
04:19	Earth changes its direction of revolution at every point on the orbit.
04:25	Notice that direction of Earth's velocity is perpendicular to Sun's gravitational pull.
04:32	Now, let us count Earth Days.
04:35	Click on Reset arrow to bring the sun and earth to its default position.
04:42	Observe the changes in the Earth Days as earth orbits the sun.
04:48	Now we will change the animation to slow, to count the days precisely.
05:00	Click on Pause to pause the simulation.
05:04	Earth takes 365 days to complete one revolution.
05:09	Next we will see what happens to earth in the absence of gravity.
05:14	Click on off radio button.
05:17	Now we will change the animation to normal.
05:21	Then click on Play button.
05:24	Observe that in the absence of Gravity, Earth files off along a straight line.
05:31	This motion is tangential to the circular path.
05:35	Click on Return Objects button.
05:38	Earth will return to its default position.
05:42	Now we will see the effect of change in mass on an orbit.
05:48	By default, the Star Mass slider is at Our Sun.
05:53	Let's drag the Star Mass slider towards 1.5.
05:58	As you drag, observe the increase in size of the star.
06:03	Next, click Gravity's on radio button and then Play button.
06:10	Observe the path of the orbit.
06:13	Earth now moves in an elliptical path.
06:17	Size of the orbit also becomes small.
06:21	Here, sun is not at the centre of the orbit.
06:26	Note that Earth Days decrease with the increase in the mass of the sun.
06:32	Drag the Planet Mass slider towards 1.5.
06:37	Notice that force of gravity between them increases.
06:42	Click on Pause button to pause the simulation.
06:46	Click on the planet and drag it away from the sun.
06:51	Click on the Play button.
06:53	Observe that gravitational force decreases with increase in the distance between planet and sun.
07:01	Click on Pause button. Click on Reset button to reset the system.
07:08	Now select Sun, Earth and Moon system.
07:12	Drag the slider towards plus sign (+) to zoom in the view.
07:17	Then click on Play button.
07:20	Notice that moon is in spiral orbit with earth while earth is in circular orbit with sun.
07:29	Here moon is a satellite of the earth.
07:34	As an assignment, using Model screen, explore earth, moon and earth, satellite systems.
07:43	Now we will move on to To Scale screen.
07:47	Click on To Scale screen at the bottom of the interface.
07:52	To Scale screen has same tools as that of Model screen.
07:57	This screen has two additional check-boxes- Mass and Measuring Tape.
08:04	Click on Mass, Path and Grid check-boxes.
08:09	By default, sun and earth system is selected.
08:14	Here, star's mass is 333 thousand Earth masses and planet's mass is 1 Earth mass.
08:24	Click on Play button to show the path of revolution.
08:28	Then click on pause button.
08:31	Let's measure the distance between star and Earth.
08:35	Check against Measuring Tape check-box.
08:39	Uncheck Mass check-box.
08:42	This will enable us to measure the distance precisely.
08:47	Drag the zoom in slider towards plus sign (+) to zoom in the view.
08:52	Place the Measuring Tape on star and drag the other end to the planet.
09:00	Note the distance between star and planet.
09:04	It is 91503 thousand miles.
09:10	This value may vary a little in your case because sun is also in motion.
09:17	Let us calculate gravitational force between Earth and sun.
09:22	Universal law of gravitation- Force of attraction between any two objects is proportional to the product of their masses.
09:33	It is inversely proportional to the square of the distance between them.
09:38	This force is along the line joining the centers of two objects.
09:44	Gravitational force is calculated by using following formula where G is universal gravitation constant,
09:53	capital M is mass of sun,
09:58	small m is mass of earth
10:02	and d is distance between earth and planet.
10:07	We substitute the values of G, capital M, small m and d in this formula.
10:15	This will give us the value of the Gravitational force between sun and Earth.
10:21	The value is 3.6 x1022 N(newton).
10:28	As an assignment, using To Scale screen, determine the gravitational force between Earth and satellite.
10:37	Now we will move on to My Solar System PhET simulation.
10:43	I have already downloaded My Solar System simulation to my Downloads folder.
10:50	To run the simulation, open the terminal. At the prompt, type: cd Downloads and press Enter.
11:01	Then type: java space hyphen jar space my-solar-system_en.jar and press Enter.
11:17	My Solar System simulation opens.
11:21	This is the interface of My Solar System simulation.
11:26	Screen has a system drop-down box on the right side.
11:30	Here, we can select a pair of solar systems of our choice.
11:36	Below the drop-down box there is another box.
11:40	It consists of Start, Stop and Reset buttons.
11:45	We have check-boxes for System Centered, Show Traces, Show Grid and Tape Measure.
11:55	Use these check-boxes as and when required.
11:59	There is a slider to control the speed of animation.
12:03	Screen is provided with Initial Settings at the bottom.
12:08	Here we can input the mass, position and velocity values in their respective boxes.
12:16	We can also use radio-buttons to select a number of bodies.
12:20	Now click on drop down arrow.
12:24	Scroll to Sun, planet, comet and click on it.
12:28	We see 3 coloured objects planet, sun and comet.
12:37	Red coloured arrow indicates the velocity.
12:41	It is a vector quantity indicated by V in circle.
12:46	Click on Start button and observe the orbits. Comet moves around the sun in an elliptical orbit.
12:55	Click on Stop button.
12:57	Hover the mouse over Sun, Planet and comet to get their mass, current position and velocity.
13:09	Click on start button.
13:12	After a few revolutions the comet collides with the Sun and disappears.
13:19	Select Four star ballet and click on Start button.
13:25	Observe the orbits. Then click on Stop button.
13:31	Hover the mouse on the bodies to get their mass, position and velocity.
13:39	As an assignment, select various systems and observe the orbits.
13:46	Change the initial settings and observe the changes in the orbits and explain the observation.
13:54	Let us Summarise.
13:57	In this tutorial, we have demonstrated how to use Gravity and Orbits and My Solar System, PhET simulations,
14:07	Using this simulations, we have described the relation between Sun, Earth, Moon and Satellite,
04:15	studied the effect of mass and distance on gravitational force,
14:20	explained how gravity controls the motion of our solar system,
14:25	identified the variables that affect the strength of gravity,
14:30	and determined the gravitational force.
14:35	The video at the following link summarizes the Spoken Tutorial project. Please download and watch it.
14:44	The Spoken Tutorial Project team conducts workshops using spoken tutorials and gives certificates on passing online tests.
14:54	For more details, please write to us.
14:58	Please post your timed queries on this forum.
15:03	This project is partially funded by Pandit Madan Mohan Malaviya National Mission on Teachers and Teaching.
15:12	Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India. More information on this mission is available at this link.
15:25	This is Meenal Ghoderao from IIT Bombay. Thank you for joining.

Contributors and Content Editors

Madhurig, PoojaMoolya, Sandhya.np14