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State Newton’s Universal Law of gravitation
Every single point mass attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of their separation
Define ‘gravitational field’
A region of space where a mass experiences a force because of its mass
Define ‘gravitational field strength’
The force per unit mass experienced by a small point mass placed in the field
What is gravitational field strength measured in?
N kg^-1
Is gravitational field strength a scalar or vector quantity?
Vector
When drawing field lines, how do you show the field strength?
thick lines = high field strength
Define gravitational potential
The gravitational potential is the work, per unit mass, on a small test mass in bringing it from infinity to a position
Define gravitational potential energy of a system
It is the work done to assemble the system from infinite separation of the components of the system
Define gravitational potential energy for a two-body system
Define escape speed
The minimum speed required for an object launched from the surface of a planet to reach infinity
What must be present for a body to travel in a circle?
an unbalanced force (centripetal force) acting toward the centre
State Kepler’s first law
Planetary orbits are elliptical with a star at a focus
State Kepler’s second law
The radius vector from the star to the orbiting body sweeps equal areas in equal times
What is the semi-major axis of an ellipse?
The distance from the center of the ellipse to the farthest point on the perimeter
An orbiting body gets ______ (faster/slower) as it gets closer to the star
faster
What are planets and stars?
point masses
Gravitational forces are always ____
attractive
How are equipotential lines drawn with respect to gravitational potential?
Equipotential lines are perpendicular to gravitational field lines
How do equipotential lines change as they get further away from the planet?
They get further apart from each other
What happens to the total energy as the orbital radius increases?
Total energy increases
What happens to the kinetic energy is the orbital radius of a satellite increases?
Kinetic energy decreases
What happens to the potential energy if the orbital radius of a satellite increases?
Potential energy increases
Note 
Flashcard (50)