Gravitation 1 Flashcards
what are kepler’s laws of planetary motion
(i) Law of orbits: All planets move in elliptical
orbits with the Sun situated at one of the foci of the ellipse.
The closest point of approach of the planet to the sun is called perihelion while farthest point is called aphelion.
(ii) Law of Areas: The line that joins any planet
to the sun sweeps equal areas in equal intervals
of time
(iii) Law of Periods:
The square of time period of revolution of any planet around the sun is directly proportional to the cube of the semimajor axis of ellipse traced out by planet.
what is another application of laws of areas
- it is a consequence of conservation of angular momentum.
- gravitational force acts as central force
- the direction and magnitude of angular momentum is conserved.
what is the universal law of gravitation
Every body in the universe attracts every other
body with a force which is directly proportional
to the product of their masses and inversely
proportional to the square of the distance
between them.
properties of gravitational force
- it is always attracive in nature
- it is independent of the medium
-it is the weakest force in nature - it forms an action reaction pair
- it is a long range force
2 imp points to keep in mind abt grav field
The force of attraction between a hollow
spherical shell of uniform density and a
point mass situated outside is just as if
the entire mass of the shell is
concentrated at the centre of the shell.
The force of attraction due to a hollow
spherical shell of uniform density, on a
point mass situated inside it is zero.
what is G (universal gravitational constant)
-scalar quanity
G=Fd2/m1m2
Nm2/kg2
G= 6.67 x 10-11
Its value is same throughout the universe; G does not depend on the nature and size of the bodies; it does
not depend even upon the nature of the medium between the bodies.
Its value was first found out by the scientist “Henry Cavendish” with the help of “Torsion Balance” experiment.
what is acceleration due to gravity
the acceleration experienced by a body due to the gravitational force of the earth.
what is gravitational potential energy
the grav potetnial energy of a body at a pointis the amount of work done in moving a particle from infinity to that point,w/o changing its speed.
PE at infinity is max and =0.
as long as the body is bound to a system, it i will have -ve poential energy.
what is gravitational potential
the gravitational potential at a point is the amount of work done in bringing a body of unit mass from inifnity to that point, wtihout changing its kinetic energy or w/o acceleration.
what is escape speed
the minimum speed with which a body is projected so that it never returns to the surface of the earth is called escape speed. A body thrown with escape speed is free of the gravitational pull of the earth.
approx 11.2 km/s
why does moon not have an atmosphere while earth does.
the gas molecules of the earth atmosphere have thermal speeds much less than the escape velocity of earth and remain bound to the earth.
moon is small and has a smaller escape velocity. so the gas molecules have thermal speeds greater than theescape velocity of moon so moon has no atmosphere.
what si orbital velocity of earth
It is the velocity required to put a satellite into orbit around earth.. A satellite moves around earth with orbital velocity
why does an astronaut feel weightless in a space ship
In a satellite around the earth, every part
and parcel of the satellite has an acceleration
towards the centre of the earth which is exactly the value of earth’s acceleration due to gravity
at that position. Thus in the satellite everything
inside it is in a state of free fall. This is just as
if we were falling towards the earth from a height.
Thus, in a manned satellite, people inside
experience no gravity.
