12p2 Gravitational Fields Flashcards
What is a gravitational field
It is a region where objects with a mass experience a force
What is gravitational field strength
The force per unit mass exerted by a gravitational field on an object
What is the formula for gravitational field strength
g = F/m where F is the force exerted on the object and m is the mass of the object
What is Newton’s law of universal gravitation
The gravitational force between two masses is directly proportional to the product of the masses and inversely proportional to the square distance between them F = Gm1m2 / r2 where G is the gravitational constant, m1 and m2 are masses and r is the distance between the centre of the masses
How to derive the equation for gravitational field due to point mass
Sub F = mg into F = Gm1m2 / r2 to get g = Gm/r2
What is gravitational potential
Gravitational potential at a point is the work done per unit mass when moving an object from infinity to that point - the gravitational potential at infinity is zero and as the object moves closer, energy is released so gravitational potential is always negative
What’s the equation for gravitational potential
V = -GM/r where M is the mass and r is the distance between centres
What is gravitational potential difference
The energy needed to move a unite mass between two points given by work done = mV where m is the mass and V is the gravitational potential difference
Compare electric and gravitational fields
The similarities are that both forces follow the inverse square law, the field lines are used to represent both uniform and radial fields and the equations are of similar form - the differences is that gravitational fields will always be attractive whereas electric field can be attractive or repulsive and electric force acts on charged objects whereas gravitational force acts on objects with mass
What is Kepler’s third law
The sqaure of the orbital period is directly proportional to the cube of the radius T2 ∝ r^3
