# Physics - Recall for Chapter 18: Gravitational Fields

> Source: https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-18-gravitational-fields/ · Updated: 2022-04-20 · Tags: physics, a-level, school, recall-questions

## Flashcards
### 2022-04-23
##### What is a gravitational field??
A region in which a mass will experience a gravitational force.

##### What is gravitational field strength??
The force per unit mass exerted on a test mass at that point in the field.

##### What are the units of gravitational field strength??
$$
N\text{kg}^{-1}
$$

##### What does the direction of a gravitational field line show??
The direction of force on a test mass at that point in the field.

##### What is represented by the spacing of field lines in a field line diagram??
Field strength.

##### What is a radial gravitational field??
A gravitational field produced by a point mass.

##### What does a radial gravitational field look like??
Many lines all pointing towards the centre of mass.

##### What is a uniform gravitational field??
A region in which the gravitational field strength is constant.

##### How is a uniform gravitational field shown in a field line diagram??
Parallel, equally spaced field lines.

##### What is a point mass??
An idealised mass with zero size.

##### What is Newton's Law of Gravitation??
The gravitational attraction between two objects is proportional to the product of their masses and inversely proportional to the square of their separation

##### What is Kepler's 1st law??
A planet's orbits is an ellipse with the Sun at one of the two foci.

##### What is Kepler's 2nd law??
The line segment joining a planet to the sun sweeps out equal areas in equal times.

##### What is Kepler's 3rd law??
The square of orbital period is proportional to the cube of the average radius.

##### How does gravitational field strength vary with distance from a point mass??
It follows an inverse square law.

##### What are the three conditions for a satellite to be in a geostationary orbit??
* There's a period of 24 hours
* It is above the equator
* It moves in the same direction as the Earth's rotation

##### What is gravitational potential??
The work done per unit mass to move an object from infinity to a point in the field.

##### How does gravitational potential vary with distance from a point mass??
It is inversely proportional.

##### What is gravitational potential energy??
The work done to move an object from infinity to a point in the gravitational field.

##### What does the negative sign mean in the gravitational potential equation??
The force is attractive.

##### What does a plot of gravitational potential against distance show??
A negative hyperbola.

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