5.4 Gravitational Fields Flashcards
What causes gravitational fields?
Any object with mass
How do gravitational field lines represent gravitational fields? (3)
At right angles to object
Arrows show direction of force (always attractive)
Separation of lines shows strength of field
Define gravitational field strength
The gravitational force exerted per unit mass at that point in the gravitational field
How is gravitational field strength and distance related?
Gravitational field strength is inversely proportional to the distance from the centre of mass of the object
What is assumed about the Earth’s gravitational field strength?
It is constant close to the surface of the Earth as the field is considered to be uniform
What does Newton’s law of gravitation assume? (2)
Point masses
Mass is concentrated at centre of mass
Why is there a negative sign in Newton’s law of gravitation?
Gravity is always an attractive force
What is Kepler’s first law of planetary motion?
The orbit of a planet is an ellipse with the sun at one of the two foci
How is a gravitational field shown to be uniform?
Equidistant, parallel field lines
State Newton’s law of gravitation
The force between two point masses is directly proportional to the product of the masses and inversely proportional to the square of their separation
What is eccentricity?
A measure of how elongated a circle is
What is Kepler’s second law of planetary motion?
A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time
What is Kepler’s third law of planetary motion?
The square of the orbital period of a planet is directly proportional to the cube of its average distance from the Sun
How is Kepler’s third law derived? (3)
Model the planetary orbit as a circle
Centripetal force on planet = gravitational force on planet
Determine speed by dividing circumference by orbital period
What is a geostationary satellite?
A satellite that stays above the same area of Earth
