Section 7 part 2- Gravitation Flashcards
What is affected in a gravitational field?
Any mass
What quantity are fields?
Vectors as they have a direction
What do field lines represent?
The direction of force that will act on an object when the object is put in the field
How do you draw a field diagram with a point?
Field lines equally spaced and finishing on the object
State what a field is
A volume of space where a force can act
Describe a gravitational field diagram and what the force is
Attractive force, looks like a negative radial field
Describe how to draw a uniform field
Field lines parallel and equally spaced and hit surface perpendicularly
How can you determine the field strength?
Density of field lines. Higher density = stronger field
What is the acceleration for an object when in free fall?
g, 9.81 ms^-2 when ignoring other forces such as air resistance
Define gravitational potential
Work done per unit mass to move a small object from infinity which is defined as 0, to that point. All gravitational potentials are negative
Why are gravitational potential energies negative?
Infinity is defined as 0 energy, and it takes energy to push out to r=infinity. Field loses energy as you move out, and this energy is normally transferred to kinetic
What is gravitational potential energy?
Work done per unit mass to move from the initial potential energy to the final potential energy
Describe lines of equipotential, and how you would draw them on a diagram
The lines space out as you go away from the centre, proportional to 1/r^2. They trace lines of equal voltage/electric potential and are perpendicular to field lines
What is potential gradient?
The amount of change in potential per unit length
Describe polar orbit
Low earth orbit - Earth rotates around underneath it, it will scan the whole Earth regularly as orbit goes over poles. 90 min orbit
Describe geostationary orbit
Above equator and takes 24 hours to orbit the Earth. Also in an equatorial plane. Stays above same place of the Earth
Give some examples of satellites in LEO, and a use
ISS, Hubble. Scan crop coverage or sea height
Give a use of MEO
GPS
Give a use of geostationary orbit
Communications
Define gravitational field
The force field around a mass
What is the strength of a gravitational field?
The force per unit mass on a small test mass placed in the field
Describe a radial field
Where the field lines are directed towards the center and look like spokes of a wheel
What are equipotentials?
Surfaces of constant potential
What is the equation for the total energy of a satellite in orbit?
-GMm/2r
What is Kepler’s third law equation?
r^3/T^2 was the same for all planets
What is the equation for the speed of a satellite?
v^2 = GM/r (M is mass of star)
