Upcoming SlideShare
×

# Gravitation

1,745 views

Published on

Tis ppt gives u a brief glance on the following topics:
Escape Speed
Earth Satellites
Geostationary And Polar Satellites
Weightlessness

Published in: Education
0 Likes
Statistics
Notes
• Full Name
Comment goes here.

Are you sure you want to Yes No
• Great work...interesting!

Are you sure you want to  Yes  No
• hey !! nice work !! that was very useful!

Are you sure you want to  Yes  No
• Be the first to like this

Views
Total views
1,745
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
0
2
Likes
0
Embeds 0
No embeds

No notes for slide

### Gravitation

1. 1. Escape SpeedEarth SatellitesGeostationary And Polar SatellitesWeightlessness
2. 2. ESCAPE SPEED Escape speed on earth (or any other planet) is defined as the minimum speed with which the body has to be projected vertically upwards from the surface of the earth(or any other planet) so that it just crosses the gravitational field of earth(or of that planet) and never returns on its own. For a spherically-symmetric body, escape velocity is calculated by the formula : Where G is the universal gravitational constant G=6.67×10−11 m3 kg−1 s−2 . M the mass of the planet, star or other body, and r the distance from the center of gravity
3. 3. Important points :  The value of escape speed does not depend on the mass (m) of the body and its angle of projection from the surface of earth or a planet.  It depends on the radius of the planet from the surface of which the body is projected.  If a body is projected from a planet with a speed v which is smaller than the escape speed ve (i.e., v < ve), the body will reach a certain height and may either move in an orbit around the planet or may fall back to the planet .  The escape velocity from the surface of the Earth is about 11.2 km/s or 25,055 miles per hour.
4. 4. Problems With Equation Near Earth The calculated escape velocity from gravity near the Earths surface of 11.2 km/s or 26,000 miles per hour is too high to be practical. Also, the effect of the Sun is not taken into account.Assumes extremely high acceleration : A major problem with the escape velocity from gravity value is that the velocity is calculated at or near the Earths surface. An infinite acceleration would be required to project an object at 11.2 km/s from the Earths surface. Also, it would be very difficult—if not impossible—for a rocket to attain a velocity of 11.2 km/s relatively close to the Earths surface. The Saturn rocket that was used to go to the Moon did not reach that speed until it was over 193 km (180 miles) from the Earths surface.Rocket would burn up Also, in order to reach the escape velocity at lower altitudes, the rocket would be traveling at hypersonic speed, which would be so far above the speed of sound that it could cause the burn-up of a rocket exterior before it left the Earths atmosphere. Realistically, a rocket would have to build up its speed until it reached the extreme upper atmosphere, where air resistance is negligible at high speeds.
5. 5. Earth Satellites Earth satellites are the objects which revolve around the earth. Their orbits around the earth are circular or elliptic. Moon is the only natural satellite of the earth with a near circular orbit with a time period of approximately 27.3 days which is roughly equal to the rotational period of the moon about its own axis. With the advancements of science and technology, since 1957, many man made satellites have been put in different orbits around the earth. Russians were the first to launch the artificial satellite Sputnik I, on Oct 4, 1957. India launched its first artificial satellite,Aryabhatta in 1957. Since the Indi has put many satellites in various orbits around the earth e.g., Bhaskara, Rohini, Apple, IA, IB, Insat, IRS etc.
6. 6. Orbital Speed : Orbital speed of a satellite is the minimum speed required to put the satellite into a given orbit around earth. Expression - v = sqrt(Re.g) Where, g=9.8 m/s & Re = radius o of earth. The value for orbital velocity was found to be 7.9 km/s. It is independent of mass of the satellite. Decrease with an increase in the radius in the radius in the height of satellite. Depends upon the mass and radius of the earth/planet around which the revolution of satellite is talking place. The direction of orbital speed of a satellite at an instant is along the tangent to the orbital path of satellite at that instant.
7. 7. Time Period And Height Of A Satellite Time period of a satellite is the time taken by satellite to complete one revolution around the earth and is denoted by T. By substituting the values we get, T = 84.6 minutes. It means that a satellite orbiting close to the surface of the earth has a time period of revolution about 84.6 minutes. The height of a satellite is given by the exp. By substituting the values, h=36000m
8. 8. Geostationary And Polar Satellites:  A satellite whose period of revolution is 24 hours, is a geostationary satellite.  It always appears to be at a fixed point in space, because the period of rotation of the Earth about its own axis is also equal to 24 hours.  Knowing T = 24 hours, g = 9.8 ms-1, the height of a geostationary satellite is calculated to be 36000km.Its orbital velocity is 3.1 km/s.  Its plane of orbit is the equatorial plane.  It revolves from west to east which is similar to the Earths movement.  It is very useful in telecommunication.
9. 9.  Polar orbiting weather satellites circle the Earth at a typical altitude of 850 km (530 miles) in a north to south (or vice versa) path, passing over the poles in their continuous flight. Polar satellites are in sun- synchronous orbits, which means they are able to observe any place on Earth and will view every location twice each day with the same general lighting conditions due to the near- constant local solar time. Polar orbiting weather satellites offer a much better resolution than their geostationary counterparts due their closeness to the Earth. Satellites in polar orbits are used for environmental and earth resources survey
10. 10. Different types of satellites :Astronomy satellites - Hubble Space TelescopeAtmospheric Studies satellites - PolarCommunications satellites - Anik ENavigation satellites - NavstarReconaissance satellites - Kennan, Big Bird,LacrosseRemote Sensing satellites - RadarsatSearch and Rescue satellites - Cospas-SarsatSpace Exploration satellites - GalileoWeather satellites - Meteosat
11. 11. Weightlessness When the astronaut in the spaceship is orbiting the Earth, then both, the astronaut and the spaceship are in a state of free fall towards the Earth. During a free fall, both travel downwards with the same acceleration, equal to the acceleration due to gravity. As a result, the astronaut does not exert any force on the sides or floor of the spaceship, and the sides and floor of the spaceship do not push the astronaut up. The astronaut therefore experiences weightlessness while orbiting around the Earth in a spaceship.