PhET/C3/Gravity-and-Solar-system/English-timed
From Script | Spoken-Tutorial
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. |
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15:25 | This is Meenal Ghoderao from IIT Bombay.
Thank you for joining. |