Up Learn – A Level physics (AQA) – GRAVITATIONAL FORCE AND FIELD
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)
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
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3. Factors that Affect Gravitational Force 1 – Mass (free trial)
4. Factors that Affect Gravitational Force 1 – Distance (free trial)
5. Article – Distances Between Masses (free trial)
6. Point Masses (free trial)
7. Newton’s Equation for Gravity (free trial)
2. Gravitational Field Strength
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4. Calculating Gravitational Field Strength (free trial)
5. Gravitational Field around the Earth (free trial)
6. Gravitational Vector Fields (free trial)
7. Gravitational Field Lines
8. Comparing Gravitational Fields (free trial)
9. Combining Gravitational Fields
10. Calculating Combined Gravitational Fields
11. Finding Points with No Gravitation Field (free trial)
12. Graphs of Gravitational Field
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3. Gravitational Potential Energy – Work Done (free trial)
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5. Absolute Gravitational Potential Energy (free trial)
6. Combining Gravitational Potential Energies (free trial)
7. Moving a Mass in a Gravitational Field (free trial)
8. Two Equations for GPE (free trial)
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10. Escape Velocity (free trial)
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3. Values of Gravitational Potential (free trial)
4. Gravitational Potential Difference (free trial)
5. Work Done and Potential Difference (free trial)
6. Equipotentials Surface Around a Point Mass (free trial)
7. Equipotentials and Field Lines (free trial)
8. Work Done Along Equipotentials (free trial)
9. Finding Gradients of Tangents (Recap) – Article (free trial)
10. Potential Graphs and Potential Gradient (free trial)
11. Gravitational Fiend Strength and Graphs of Gravitational Potential (free trial)
12. Finding Areas Under Curves – Article (free trial)
13. Gravitational Potential and Graphs of Gravitational Field Strength (free trial)
14. Worked Example – Finding Potential Difference from a Field Strength Graph – Article (free trial)
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16. Combining Potentials (free trial)
17. Combining Potential Graphs (free trial)
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4. Proving Kepler’s Third Law (free trial)
5. Recap of Log Laws – Article (free trial)
6. Graphing Kepler’s Third Law (free trial)
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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.