Chapter 18 - Gravitational Fields Flashcards
How is a uniform gravitational field shown?
Field lines are parallel and equidistant, gravitational field strength does not change.
Newton’s law of gravitation
F ∝ Mm
F ∝ 1/r squared
What does the negative sign indicate for gravitational fields?
They are attractive.
Kepler’s first law
The orbit of a planet is an ellipse with the Sun at one of the two foci.
Why are orbits usually modelled as circles?
Orbits have low eccentricity.
Kepler’s second law
A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time
Kepler’s third law
T squared ∝ r cubed
T is the orbital period of a planet, r is the distance from the Sun.
Satellite uses
- Communication - TV, radio.
- Military reconnaissance.
- Scientific research e.g. monitoring pollution and studying the Universe.
- Monitoring weather and climate.
- GPS.
Polar orbit
Circles poles, low Earth orbit.
Geostationary orbit
Orbit above the equator.
Geostationary satellite
Remains in same place above Earth while it rotates.
Orbits above the equator.
Rotates in same direction as Earth’s rotation.
T is 24 hours.
Gravitational potential
Work done per unit mass to move an object to that point from infinity. It is zero at infinity.
Scalar quantity.
What happens to the gravitational potential when moving towards a point mass?
Gravitational potential decreases.
What is the area under a force-distance graph?
Work done to move mass (e.g. from point B to A).
Escape velocity
Minimum velocity at which an object has enough energy to leave a specified gravitational field.
