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Gravitational Fields

- Astrophysics
- Absolute Magnitude
- Astronomical Objects
- Astronomical Telescopes
- Black Body Radiation
- Classification by Luminosity
- Classification of Stars
- Cosmology
- Doppler Effect
- Exoplanet Detection
- Hertzsprung-Russell Diagrams
- Hubble’s Law
- Large Diameter Telescopes
- Quasars
- Radio Telescopes
- Reflecting Telescopes
- Stellar Spectral Classes
- Telescopes
- Atoms and Radioactivity
- Fission and Fusion
- Medical Tracers
- Nuclear Reactors
- Radiotherapy
- Random Nature of Radioactive Decay
- Thickness Monitoring
- Circular Motion and Gravitation
- Applications of Circular Motion
- Centripetal and Centrifugal Force
- Circular Motion and Free-Body Diagrams
- Fundamental Forces
- Gravitational and Electric Forces
- Inertial and Gravitational Mass
- Vector Fields
- Electricity
- Attraction and Repulsion
- Basics of Electricity
- Batteries
- Circuit Symbols
- Circuits
- Current-Voltage Characteristics
- Electric Current
- Electric Motor
- Electrical Power
- Electricity Generation
- Emf and Internal Resistance
- National Grid Physics
- Ohm's Law
- Potential Difference
- Power Rating
- Resistivity
- Series and Parallel Circuits
- Static Electricity
- Superconductivity
- Transformer
- Voltage Divider
- Electricity and Magnetism
- Energy Physics
- Big Energy Issues
- Conservative and Non Conservative Forces
- Efficiency in Physics
- Elastic Potential Energy
- Electrical Energy
- Energy and the Environment
- Forms of Energy
- Geothermal Energy
- Gravitational Potential Energy
- Heat Engines
- Heat Transfer Efficiency
- Kinetic Energy
- Potential Energy
- Potential Energy and Energy Conservation
- Pulling Force
- Renewable Energy Sources
- Wind Energy
- Engineering Physics
- Angular Momentum
- Angular Work and Power
- Engine Cycles
- First Law of Thermodynamics
- Moment of Inertia
- Non-Flow Processes
- PV Diagrams
- Reversed Heat Engines
- Rotational Kinetic Energy
- Second Law and Engines
- Thermodynamics and Engines
- Torque and Angular Acceleration
- Fields in Physics
- Alternating Currents
- Capacitance
- Capacitor Charge
- Capacitor Discharge
- Coulomb’s Law
- Electric Field Strength
- Electric Fields
- Electric Potential
- Electromagnetic Induction
- Energy Stored by a Capacitor
- Escape Velocity
- Gravitational Field Strength
- Gravitational Fields
- Gravitational Potential
- Magnetic Fields
- Magnetic Flux Density
- Magnetic Flux and Magnetic Flux Linkage
- Moving Charges in a Magnetic Field
- Newton’s Laws
- Operation of a Transformer
- Parallel Plate Capacitor
- Planetary Orbits
- Synchronous Orbits
- Force
- Air resistance and friction
- Conservation of Momentum
- Contact Forces
- Elastic Forces
- Force and Motion
- Gravity
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- Moment Physics
- Moments and Equilibrium
- Moments, Levers and Gears
- Pressure
- Resultant Force
- Safety First
- Time Speed and Distance
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- Work Done
- Further Mechanics and Thermal Physics
- Bottle Rocket
- Charles law
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- Temperature
- Thermal Physics
- Volume
- Kinematics Physics
- Magnetism
- Ampere force
- Earth's Magnetic Field
- Fleming's Left Hand Rule
- Induced Potential
- Motor Effect
- Particles in Magnetic Fields
- Measurements
- Mechanics and Materials
- Acceleration Due to Gravity
- Bouncing Ball Example
- Bulk Properties of Solids
- Centre of Mass
- Collisions and Momentum Conservation
- Conservation of Energy
- Density
- Elastic Collisions
- Force Energy
- Friction
- Graphs of Motion
- Linear Motion
- Materials
- Materials Energy
- Moments
- Momentum
- Power and Efficiency
- Projectile Motion
- Scalar and Vector
- Terminal Velocity
- Vector Problems
- Work and Energy
- Young's Modulus
- Medical Physics
- Absorption of X-Rays
- CT Scanners
- Defects of Vision
- Defects of Vision and Their Correction
- Diagnostic X-Rays
- Effective Half Life
- Electrocardiography
- Fibre Optics and Endoscopy
- Gamma Camera
- Hearing Defects
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- Lenses
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- Noise Sensitivity
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- Physics of Vision
- Physics of the Ear
- Physics of the Eye
- Radioactive Implants
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- Structure of the Ear
- Ultrasound Imaging
- X-Ray Image Processing
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- Modern Physics
- Nuclear Physics
- Alpha Beta and Gamma Radiation
- Binding Energy
- Half Life
- Induced Fission
- Mass and Energy
- Nuclear Instability
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- Safety of Nuclear Reactors
- Particle Model of Matter
- Physical Quantities and Units
- Converting Units
- Physical Quantities
- SI Prefixes
- Standard Form Physics
- Units Physics
- Use of SI Units
- Physics of Motion
- Acceleration
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- Angular Velocity
- Centrifugal Force
- Centripetal Force
- Displacement
- Equilibrium
- Forces of Nature Physics
- Galileo's Leaning Tower of Pisa Experiment
- Mass in Physics
- Static Equilibrium
- Radiation
- Antiparticles
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- Atomic Model
- Classification of Particles
- Collisions of Electrons with Atoms
- Conservation Laws
- Electromagnetic Radiation and Quantum Phenomena
- Isotopes
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- Particles
- Photons
- Protons
- Quark Physics
- Specific Charge
- The Photoelectric Effect
- Wave-Particle Duality
- Scientific Method Physics
- Data Collection
- Data Representation
- Drawing Conclusions
- Equations in Physics
- Uncertainties and Evaluations
- Space Physics
- Torque and Rotational Motion
- Turning Points in Physics
- Cathode Rays
- Discovery of the Electron
- Einstein's Theory of Special Relativity
- Electromagnetic Waves
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- Electron Specific Charge
- Length Contraction
- Michelson-Morley Experiment
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- Newton’s and Huygens’ Theories of Light
- Photoelectricity
- Relativistic Mass and Energy
- Special Relativity
- Thermionic Electron Emission
- Time Dilation
- Wave Particle Duality of Light
- Waves Physics
- Acoustics
- Applications of Ultrasound
- Applications of Waves
- Diffraction
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- Earthquake Shock Waves
- Echolocation
- Image Formation by Lenses
- Interference
- Light
- Longitudinal Wave
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- Mirror
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- Properties of Waves
- Ray Diagrams
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- Reflection
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- Refraction at a Plane Surface
- Resonance in Sound Waves
- Seismic Waves
- Snell's law
- Standing Waves
- Stationary Waves
- Total Internal Reflection in Optical Fibre
- Transverse Wave
- Ultrasound
- Wave Speed
- Waves in Communication
- X-rays

You must have heard the phrase ‘what goes up must come down’. In physics terms, as Sir Isaac Newton discovered, what goes away from the earth will be pushed back towards it. So, when you throw a ball in the air, whether it goes straight up, to the left, or to the right, it eventually falls back to the ground. And this is true regardless of the height from which the ball is released.

In fact, it takes a significant amount of force, such as the engines of an aeroplane and the lift force produced by the wings, to keep pushing an object away from the earth. Without these forces, it would fall out of the sky.

Gravity is a force that attracts all objects that have a mass to each other. As the earth has a mass, it attracts other objects towards it. The same is true for other objects, which similarly attract each other towards themselves, including the earth. Even we attract the earth towards ourselves with the force of gravity.

But why isn’t this obvious? Why don’t we see other objects attract each other, given that they all have mass? We will consider this in what follows.

A force field is a region in which an object experiences a non-contact force.

Force fields cause an interaction between objects and particles without the objects touching each other. In the case of gravity, that interaction happens between masses. Any object will experience an attractive force if you put it in the gravitational field of another object.

Force fields can be represented as a system of vectors, as in this diagram, in which the arrows represent the gravitational field on the earth.

The earth’s gravitational field is radial, which means that the lines of force intersect at the centre of the earth.

As the diagram shows, the field lines are closer together at the surface of the earth. This indicates that the gravitational force is stronger here. Where the lines move further apart from each other, the force decreases.

Have a look at the equation below, which represents **Newton’s law of gravitation**:

*F*= magnitude of the gravitational force.

*G*= gravitational constant.*r*= distance between the centres of two masses.- = mass of one of the objects.
- = mass of the other object.

Newton’s gravitational field: when two bodies are placed in a gravitational field, they experience a force that is the product of the two masses and the inverse square of the distance from the centre of both masses.

The constant G is a gravitational constant, which has a very small value:

Calculate the gravitational force between two 3kg spheres that are 2m apart.

The mass of both objects is 3kg. So m1 and m2 are 3kg, while r is 2m, with G being 6.67 * 10 ^ -11 Nm ^ 2 / kg ^ 2. Putting in all the values gives us:

The gravitational constant G, which, as we said, has a very small value, is the reason why objects don’t fly and collide with each other. It is also the reason why the earth is not attracted to us but we to it. After all, our mass is negligible compared to that of the earth.

The distance between the two objects has more impact than their masses because Newton’s gravitational equation follows an inverse square law. This means that if the distance doubles, the force is one-quarter of the strength of the original force.

The force of a single mass is its gravitational field strength, which is defined as force per unit mass when it is placed in a gravitational field.

*g*is measured in units of newtons per kilogram ().*F*is the force experienced by mass m when it is placed in a gravitational field.

As the gravitational field on the earth’s surface is almost uniform, we can assume g to be constant. Hence, g is just the acceleration of mass m in a gravitational field.

Point masses are objects that behave as if all mass is concentrated at their centre. Uniform shapes have a point mass.

The significance of point masses is that they have a radial gravitational field. In this, the field lines radiate from its centre. For point masses, our earlier equation becomes:

- g = gravitational field strength (N/kg).

- m = mass of the object (kg).
- G = gravitational constant ().
- r = distance from the centre (m).

The gravitational force depends on the mass of the planet. Mars, for instance, has a gravitational field strength of 3.71 N/kg because it is only about half the diameter of the earth. But, and here comes the interesting part, your weight also depends on the gravitational force g.

Your mass is the same wherever you go in the universe. What differs is your weight, which depends not only on your mass but also on gravity. So, for instance, if you weigh 99.8kg on earth, you would only weigh 37.74kg on Mars.

The moon has a gravitational force of 1.62 N/kg. This is why on the moon, it is easier to fly than to walk. On Mars, walking becomes a bit easier but is still a challenge because of the low gravitational pull.

The tides that form on the surface of the earth show how both mass and distance affect the gravitational force.

We get tides on the earth’s surface because of the gravitational pull of the moon and the sun. And although the sun has far more mass than the earth, the distance between the two plays a significant role due to the inverse square proportionality. As the moon is much closer to the earth, the earth’s oceans respond to the moon revolving around the earth, which causes the tides. The sun does have an impact, too, but the tides produced by the sun are much smaller.

- Gravity is all about masses attracting one another.
- A gravitational field is a force field in which an object experiences a force.
- Only large masses, such as the sun, the moon, and other planets, have a significant gravitational force.
- Newton’s law of gravitation is:
The law of gravitation is an inverse square law, which says that the gravitational force decreases when the distance between the objects increases.

Gravitational field strength is force per unit mass acting on an object placed in a gravitational field.

In a radial field, the gravitational field can be represented as:

The gravitational field strength on earth is 10 N/kg.

Gravitational field strength is calculated as follows:

g=F/m

It is measured in Newtons per kilogram (N/kg).

This can be calculated using the equation below:

weight = mass * gravitational field strength

w=m*g

More about Gravitational Fields

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