Gravitational Fields Flashcards
(20 cards)
What are field lines?
- A line representing the path that a mass would take when placed within the field
What is a geostationary satellite?
- A satellite that orbits above above the equator with a 24 hour period
- Hence why it will always remain above the same position on the Earth
- They orbit approximately 36,000 km above the surface of the Earth
What is a Gravitational Field?
- A region of space where objects with mass experience an attractive force due to gravity
What is Gravitational Field Strength?
- The gravitational force on a object divided by its mass
- it is the acceleration due to the gravitational field
What is Gravitational Potential?
- Defined at a point
- the amount of work done in moving a unit mass from an infinite distance to that point
What is Gravitational potential Energy?
The component of an object’s energy due to its position in a gravitational field.
What are Synchronous Orbits?
- An orbit with a time period of one day, which means the orbiting body will return to the same point in the sky each day
What is gravity?
- Universal attractive force that acts between all mass-possessing matter
What is G?
- The universal gravitational constant
- approx. G = 6.67 x 10^-11 N m^2/kg^2
What is the magnitude of the average gravitational field strength on the surface of the Earth?
- 9.81 ms^-2 OR 9.81 Nkg^-1
- this means a force of attraction of 9.82 N is experienced between an object and the Earth’s surface for every kilogram that the object weighs
- F= ma explains why both units are acceptable
What can field lines tell you about a field?
- The direction of the field
- the strength of the field, which depends on the number of the field lines per unit area
What is g?
- is the force per unit mass in a uniform gravitational field
- In a radial field:
- the magnitude of g is the proportionality constant at that point between force and mass
- g = GM/r^2
What is Newton’s law of gravitation?
- states that the gravitational force acting between two point masses is directly proportional to the product of their masses and inversely proportional to the square of the distance between them
- F = GMm/ r ^2
Derive the equation for the gravitational field strength of a radial field
- starting with g = F/m
- sub in F= GMm/r^2
- get g = GMm/(r^2m)
- g = Gm/r^2
What are satellites and what are they used for?
- bodies that orbit significantly more massive bodies
- include natural ones like the moon as well as artificial ones that humans have sent into space
- Uses:
- communications
- scientific research
- Global Positioning System (GPS)
What are geostationary satellites? What are they used for?
- have an orbital period that is exactly one day.
- Means they appear stationary above the Earth
- orbit 36,000 km above the equator
- Useful for communications and surveying since they can provide continuous coverage
What is gravitational potential energy at a point in the field?
- The work done in moving an object from infinity to that point in the field
Give an equation that describes the gravitational field exerted by a body
- Φ = -GM/r
- where:
- ‘Φ’ is the gravitational potential
- ‘G’ is the universal gravitational constant
- ‘M’ is the mass of the body
- ‘r’ is the distance of the body to the object that is subject to its field
- ‘Φ’ has the units Jkg^-1 so the potential energy between two bodies depends on the mass of the second
Give an equation that describes the gravitational potential energy between two point masses?
- E(p) = -GMm/r
- where:
- ‘E(p)’ is the GPE
- ‘G’ universal gravitational constant
- ‘M’ is the mass of the more massive body
- ‘r’ is the distance between the centre of masses of the two bodies
True or False?
At the Earth’s surface, the value of g is approximately constant
- True
- at the Earth’s surface the field is relatively uniformly so ‘g’ is approximately constant
