_{Up Learn – A Level physics (AQA) – GRAVITATIONAL FORCE AND FIELD}

_{Up Learn – A Level physics (AQA) – GRAVITATIONAL FORCE AND FIELD}

**Gravitational Field Lines**

**Gravitational Field Lines****How we use gravitational field lines to represent gravitational field strength in uniform and radial fields.**

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### More videos on Gravitational Force and Field:

^{Introduction to Gravitational Fields (free trial)}

^{Gravitational Field Strength}

^{Test Masses (free trial)}

^{Calculating Gravitational Field Strength (free trial)}

^{Gravitational Field around the Earth (free trial)}

^{Gravitational Vector Fields (free trial)}

^{Comparing Gravitational Fields (free trial)}

^{Combining Gravitational Fields}

^{Calculating Combined Gravitational Fields}

^{Finding Points with No Gravitation Field (free trial)}

## Gravitational Force and Field

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2. Reminder About Gravity

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3. Factors that Affect Gravitational Force 1 – Mass

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4. Factors that Affect Gravitational Force 1 – Distance

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5. Article – Distances Between Masses

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6. Point Masses

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7. Newton’s Equation for Gravity

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2. Gravitational Field Strength

3. Test Masses

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4. Calculating Gravitational Field Strength

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5. Gravitational Field around the Earth

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6. Gravitational Vector Fields

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7. Gravitational Field Lines

8. Comparing Gravitational Fields

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9. Combining Gravitational Fields

10. Calculating Combined Gravitational Fields

11. Finding Points with No Gravitation Field

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12. Graphs of Gravitational Field

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2. Changes in Gravitational Potential Energy in a Uniform Field

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3. Gravitational Potential Energy – Work Done

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4. Gravitational Potential Energy at Infinity

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5. Absolute Gravitational Potential Energy

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6. Combining Gravitational Potential Energies

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7. Moving a Mass in a Gravitational Field

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8. Two Equations for GPE

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9. Deriving Two Equations for Ep – Article

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10. Escape Velocity

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2. The Gravitational Potential

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3. Values of Gravitational Potential

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4. Gravitational Potential Difference

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5. Work Done and Potential Difference

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6. Equipotentials Surface Around a Point Mass

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7. Equipotentials and Field Lines

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8. Work Done Along Equipotentials

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9. Finding Gradients of Tangents (Recap) – Article

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10. Potential Graphs and Potential Gradient

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11. Gravitational Fiend Strength and Graphs of Gravitational Potential

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12. Finding Areas Under Curves – Article

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13. Gravitational Potential and Graphs of Gravitational Field Strength

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14. Worked Example – Finding Potential Difference from a Field Strength Graph – Article

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15. Equipotentials and Potential Gradient

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16. Combining Potentials

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17. Combining Potential Graphs

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2. Recap of Circular Motion – Article

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3. Kepler’s Third Law

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4. Proving Kepler’s Third Law

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5. Recap of Log Laws – Article

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6. Graphing Kepler’s Third Law

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7. Graphing Kepler’s Third Law – Article

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8. What are Satellites?

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9. Geostationary Satellites

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10. Polar and Geosynchronous Orbits – Article

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11. Energy of Orbiting Satellites

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12. Escape Velocity for Satellites

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Previously, we’ve seen that the gravitational field of a point mass or a spherical mass looks like this.

Now, here is the Earth and here are its gravitational field lines.

It’s a radial field because the Earth is approximately spherical.

The field lines are closer together here than here.

And we’ve seen that this means the gravitational field is stronger here than here.

Next, if we zoom in until the ground looks pretty much flat, we can see that the field lines look almost parallel to each other!

And the lines are the same distance apart here as they are here!

So when we’re zoomed in this much, the field looks pretty much uniform…

…and this makes sense, because we’ve seen that near the surface of a large mass like a planet, gravitational field strength doesn’t change significantly with height.

On the other hand, over larger distances, the field is radial and g varies with distance!

So, in summary…

The field around a spherical mass like a planet is…

The field around a spherical mass like a planet is radial so the gravitational field strength depends on distance.

But close to the surface of the planet, the gravitational field appears…

Close to the surface of the planet, the gravitational field appears uniform so using a constant value for g is pretty accurate.