# Gravitational and Electric Fields

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