Gravitational Field Flashcards
What is Newton’s law of gravitation?
Newton’s law of gravitation states that gravitational force is directly proportional to the product of two masses and inversely proportional to the square of their separation. Their separation is much greater than their diameter.
What is gravitational field strength?
Gravitational field strength is the gravitational force per unit mass acting on a small mass placed at that point
What is gravitational potential energy?
Work done by an external agent on a mass in bringing the mass from infinity to that point without a change in kinetic energy
What is gravitational potential?
Work done by an external agent in moving unit mass from infinity to that point without a change in kinetic energy
Why is acceleration of free fall near Earth’s surface constant?
- Near the surface, height is negligible as compared to the radius of the earth
- gravitational field strength g is approximately constant and uniform near the surface of Earth g= GM/R² ≈ GM/(R+h)² if h «< R
- By newton’s second law, acceleration of free fall equals to gravitational field strength
- Thus, acceleration of free fall near Earth’s surface is constant
Why is gravitational field strength g different at different parts of the earth in reality?
- Non uniform earth crust
- not a perfect sphere
- rotating earth, g measured is smaller
What does weightless mean?
Weightless implies an object experiences only its own weight, and no contact forces, N=0.
What are some examples of weightless?
-Object free falling in a frictionless environment
- geostationary satellite orbiting the earth
What is weight defined as?
gravitational force acting on a mass placed in a gravitational field, W=mg
When is an object truly weightless?
- W=0 when g=0
- object is truly weightless when it experiences no gravitational field
What are some examples of true weightlessness?
- When an object is infinitely far away from any body
- an object is placed as a point between earth and moon such that their gravitational fields cancel each other out
What are some characteristics of geostationary orbit?
- directly above the equator
- same period as earth, T=24h
- rotate in same direction as earth, west to east
What is escape velocity of earth?
The minimum velocity that a body must have at the Earth’s surface in order to escape the influence of Earth’s gravitational field
What is a geostationary satellite?
A satellite in geostationary orbit appears to be fixed over one spot above the equator. It orbits the earth in exactly one day, lies in the plane containing the equator and moves from West to East
