newton’s law of gravitation
gravitational force of attraction between 2 point masses is directly proportional to the product of their masses and inveresly proportional to the square of the separation between their centres.
gravitational field strength at a point g
gravitational field strength at a point g is the gravitational force per unit mass exerted on a small test mass placed at that point
gravitational potential energy
gpe of a mass m at a point in a gravitational field due to mass M is the work done by external force in brining that mass m from infinity to that point, without a change in kinetic energy.
gravitational potential at a point
gravitational potential at a point is work done per unit mass (by an external force) in bringing small test mass from infinity to that point
what is esape velocity
minimum velocity to be launched to escape planet’s gravitational field
what is the condition for a geostationary orbit (hint: there are 3)
orbital period of satellite is 24h, satellite must be direvtly above the equator, and must be orbiting in the same direction as earth’s rotation, from west to east
advantage of geostationary orbit
geostationary satellite appears stationary, used as telecommunication satellites and weather satellites, in constant line-of-sight to data receiving stations on earth surface
disadvantage of geostationary orbit (2)
significant distane from earth, resolution of photographs taken from that orbit is limited. orbits are near equator, so ability of satellites to serve customers at high latitudes is limited
why do astronatus in spacecraft feel ‘weightless’
experiencing apparent weightlessness since no normal force between astronaut and floor or walls of spacecraft. gravitational force only force acting on astronaut
if gravity acts on spacecraft in oribt, why doesn’t it fall to earth
grvaitiational force of earth on spacecraft is just sufficient to provide centripetal force to keep the spacecraft in circular motion. velocity must be perpendicular to gravitiational force, velocity just sufficient to keep circular motion
define geostationary orbits
satellites orbiting around the earth such that these satellites would appear stationary relative to an observer on earth
why must geostationary satellite be placed vertically above the equator
gravitational force which provides centripetal force must be directed towards the centre of earth. to be geostationary, axis of rotation of satellite is the same as axis of earth’s rotation and must lie on plane that contains equator
why must a geostationary satellite move from west to east
in order to appear stationary from a fixed location from earth’s surface, period of satellites in geostationary obrits must be the same as the rotational period of earth (24h)
why is the gravitational potential negative in value
the gravitational potential at infinity is zero. gravitational field is attractive in nature (external force opposite to gravitational force). work done by external force in moving the test mass from infinity to the point is negative, as such the gravitational potential is negative in value.
why is g-field strength near surface of earth constant and equal to acceleration of free fall
near the surface, height very small compared to radius of earth, field strength is almost constant. When free falling, gravitational force is the only force acting on the body, by newton’s 2nd law, acceleration of free fall numerically equal to gravitational field strength.
