Physics 5.4 Gravitational fields Flashcards
Define gravitational fields and what do gravitational field lines show?
-Gravitational fields: a vector quantity, it is the region around a body in which other bodies will feel a force due to the mass of the body
-Gravitational field lines show the shape of the field and direction
What is gravitational field strength?
-Gravitational field strength at any point is the force per unit mass at that point. Units are Nkg^-1
Why does the gravitational field strength of the earth vary at the surface?
-Matter is not evenly distributed across the earth, for example water is less dense than rock, so gravitational force can vary slightly
What is the value of the gravitational field strength of the earth at its surface?
9.81 NKg^-1
Define Newtons law of gravitation?
-Newton’s law of gravitation: states that the gravitational force of attraction between two point masses is directly proportional to the product of their masses and inversely proportional to the square of separation
What is the equation for Newtons law of gravitation?
-Where M and m are the masses of the bodies
-R is the separation of their centres
-G is the universal gravitational constant
What is the value of the universal gravitational constant?
Describe the gravitational field lines of a spherically symmetric mass?
-The gravitational field lines act radially towards the centre
What is the equation for gravitational force of a spherical or point object?
Where G is universal gravitational constant, M is mass of body and r is the radius of the mass
What is an equation for the gravitational field strength of the earth as height(h) above the earths surface increases
G-universal gravitational constant
R-radius of earth
H- height above earths surface
M-mass of earth
What are the definitions of Keplers third law and geostationary orbirt?
-Keplers third law: states that the square of the time period of a planet orbiting a sun is proportional to the mean radius of its orbit cubed
-Geostationary orbit: a sattelite that has the same time period and orbital rotation as the earth (24hours) so is in equatorial plane
What are keplers three laws describing planetary motion?
- Planets travel around the sun in elliptical orbits
- A line joining the sun to a planet will sweep out equal areas in equal times (explained in picture)
- The time period of the orbit squared is proportional to the mean radius of the orbit cubed
What is the equations for Keplers third law?
T-time period
R-mean radius of orbit
G-universal gravitational constant
M-mass of larger mass
What is an example of what geostationary satellites are used for?
-Monitiring air traffic, weather and changes in environment
Define gravitational potential and escape velocity?
-Gravitational potential: at a point in a gravitational field, is defined as the work done in moving unit mass from infinity to that point. Unit is Jkg^-1
-Escape velocity: from a point in a gravitational field, is the minimum launch velocity required to move the object from that point to infinity
What is the equation for escape velocity?
V-escape velocity
G-universal gravitational constant
M-mass of body
r-radius
