# Gravitational and Electric Fields

- Created by: Sagaana
- Created on: 01-06-18 19:54

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- Gravitational and Electric fields
- Gravitational field
- What is Gravitational Field
- Object with mass will experience an attractive force when put in to a gravitational field of another object
- Only objects with a large mass have a significant effect
- When mass moves further away from earths surface the weaker the force is on the object
- Earth gravitational field is radial but closer to the surface it becomes uniform
- You can calculate the force on the object using Newton's Law of Gravitation
- It is an inverse square law as radius increase the force decreases

- Gravitational Field Strength
- It is the force per unit mass
- It is a vector Quantity it points towards the center of mass
- It is constant in a Uniform Field
- In a radial Field 'g' is inversely proportional to the r^2
- This is a Inverse Square Law, as r increase the g decreases

- Gravitational potential
- It is Potential energy per unit mass
- It is negative on the surface but as the distance increases it becomes less negative.
- At infinite distance it will be Zero
- Gravitational potential energy will also be negative

- It is the work done by bringing a unit mass from infinity to that point within the field.
- Mass must travel as Escape Velocity to escape the gravitational Field. Where the mass's kinetic energy must equal its gravitational potential energy
- Gravitational Potential difference is the work done done to move an object against the force of gravity
- Equipotential lines (2D) and surface (3D) joins all the point with the same potential
- u dont lose or gain energy when u travel along an equipotential
- Gravitational Potential difference = 0
- Work done = 0
- Equipotential and Field Lines are perpendicular to each other

- Orbits and gravity
- Keplers's Law
- 1st -All planets move in elliptical orbits, with the sun at one focus.
- 2nd -A line that connects a planet to the sun covers equal areas in equal times.
- Total Energy is conserved
- In a Circular Orbit the Speed is constant as the distance from the focus doesn't change
- In a elliptical Orbit as the height increases the satellite slows down and as height decrease the satellite speeds

- 3rd - t^s =k * r^3 The square of the period of any planet is proportional to thecube of the semi-major axis of its orbit.

- Orbit types
- Geostationary orbit
- directly above the equator
- time period same as earth's rotation period
- remains at the same point on earth
- useful for communications, weather and TV

- Geosynchronous orbit
- Same angular velocity as the earth turns
- remain on the same longitude not latitude
- time period is the same as the earths rotational period
- useful for TV phone sisgnals

- Polar Orbit
- satellite passes through both poles
- inclination of 90 degrees to the equator
- Passes over the equator at different longitude on each of its orbit

- Geostationary orbit

- Keplers's Law

- What is Gravitational Field
- Electric Fields
- What is Electric Fields
- It is around a Charged Object
- Charge measured in Coulombs and it can be both negative and positive
- opposite attract and like repel
- if Object is sphere then you can assume that the charge is all at the center
- Can be represented using field lines
- You can calculate the force using Coulombs law
- The force ion Q1 equal and opposite to the force on Q2 .The direction depends on the charge
- it is an inverse square law.The further away the charges the weaker the force.

- Electric Field Strength
- Force per unit positive charge
- It is a vector that points in the direction that a positve charge would move
- Unit: newtons per coulomb
- positive charge will have the fields pointing outwards
- Negative charge will have the field pointing inwards

- Electric Potential
- It is the electrical potential energy a unit positive charge would have.
- When V is positive then Q is positive so force is repulsive. When V is negative Q is also negative so the force is attractive.
- magnitude of V is greatest when on the surface of the charge.
- It decrease as as the distance increases.
- V will be 0 when at infinite distance

- It decrease as as the distance increases.
- Electrical Potential Difference
- It is defined as zero when at infinite distance
- It is the work done on a charge from infinity to the point
- This depends on the size of the charge and the pd that you want it to move across

- Equipotentials show all the points of the Equal Potential in a field
- Point charge -> spherical surfaces
- Parallel plates -> flat planes
- No Work done when travelling along an equipotential

- What is Electric Fields
- Fields
- A reigon in which a body experiences a non-contact force.
- causes interactions between objects
- force fields can be represented as vectors

- Comparisons
- Difference
- Gravitational force is always attractive
- Electric can be both attractive and repulsive

- Similarities
- Field Strengths
- Gravitational involves unit mass
- Electric involves positive unit charge

- Field lines
- Potential (both 0 at infinity)
- Equipotential
- uniform spherical mass and point charge form a spherical surface

- Work Done

- Field Strengths
- Subatomic level
- Gravity is small because the mass is also very small.
- weaker than electrostatic
- The nucleus doesn't break apart as there is strong force holding it together

- weaker than electrostatic

- Gravity is small because the mass is also very small.

- Difference

- Gravitational field

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