Gravity Flashcards
State Newton’s Law of Gravitation
The force of attraction between two masses is directly proportional to the product of the masses and inversely proportional to the square of their separation.
Define gravitational field strength
Gravitational force per unit mass
Why do planets orbit the sun?
The force of gravity of the Sun on the planet provides a centripetal force.
State Kepler’s First Law
The orbit of a planet is an ellipse with the sun at one of the foci.
State Kepler’s Second Law
A line segment joining a planet to the Sun, sweeps out equal areas in equal time intervals.
Why does a planet travel faster when closer to the Sun?
Due to Kepler’s Second Law, when the planet is closer to the Sun, loss in GPE = gain in KE.
State Kepler’s Third Law
For the planets, the time period squared is directly proportional to the orbital radius cubed.
What are features of a geo-stationary satellite?
They stay at a point on the Earth’s surface
Has a time period of 24 hours
Orbits around the equator
Rotates from west to east like earth
What are features of a polar satellite?
They orbit at a low height
Pass over north and south poles
Have a short time period
Between successive orbits the Earth rotates
Define gravitational potential
Gravitational potential at a point is the work done per unit mass from infinity to that point, with potential defined as zero to infinity.
Define escape velocity
The minimum velocity needed to escape the gravitational force of a mass.
What do gravitational field lines show?
The arrows show the direction of the gravitational field
Density of field lines give an indication of field strength
Describe the gravitational field close to the Earth
Virtually uniform with constant strength and direction.
Describe the field lines for a mass in the Earth’s local field
Field lines are straight, parallel, equally spaced and point vertically downwards.
