Physics - Gravitational Fields

OCR A-Level Physics 2022

Created: November 18, 2021 | Read markdown | About these notes | View in context | Study these flashcards |

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Gravitational field strength

What is the equation for gravitational field strength, $g$?

field-strength-equation
\[g = \frac{F}{m}\]

What are the two possible units for gravitational field strength?

field-strength-units
\[\text{N}\text{kg}^{-1}\] \[\text{m}\text{s}^{-2}\]

What is the wordy explanation of gravitational field strength?

field-strength-wordy-definition

The gravitational force exerted per unit mass on a small object placed at a point within the field.

What simplifying assumption do we make for planets and stars when calculating gravitational fields?

point-mass-assumption

They are point masses.

What does this picture show?

uniform-field-near-surface

That the gravitational field close to a planet’s surface can be modelled as uniform.

What are the lines on a gravitational field diagram called?

field-lines-name

Field lines.

Newton’s law of gravitation

What two things does Newton’s law of gravitation state?

newtons-law-statement

The force between two point masses is:

  • Directly proportional to the product of the masses.
  • Inversely proportional to the square of their separation.

What is the equation for Newton’s law of gravitation?

newtons-law-equation
\[F = -\frac{GMm}{r^2}\]
\[F = -\frac{GMm}{r^2}\]

What is $G$ here?

gravitational-constant-symbol

The gravitational constant.

\[F = -\frac{GMm}{r^2}\]

Why is there a minus sign here?

newtons-law-minus-sign

To show that the force is attractive.

What is the approximate value of $G$, the gravitational constant?

gravitational-constant-value
\[6.67 \times 10^{-11}\]

When determining the gravitational force between multiple objects, what do you need to do?

superposition-vector-addition

Do the vector addition of all possible pairings.

Field of a planet and Earth data

What is the formula for $g$ in terms of $r$ and $M$?

field-strength-from-mass-radius
\[g = \frac{GM}{r^2}\]

What is the radius of the Earth?

earth-radius
\[6.37 \times 10^6 m\]

What is the mass of the Earth?

earth-mass
\[5.97 \times 10^{24} \text{kg}\]

What is the most common failure mode answering gravitational field questions?

common-failure-unit-conversion

Not converting distances to meters.



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