The energy an object possess due to its position in a gravitational field
The work done per unit mass in bringing a test mass from infinity to a defined point
Gravitational potential decreases as the satellite moves closer to the Earth
Gravitational potential increases and decreases depending on whether the object is travelling towards or against the field lines from infinity
A planet has a diameter of 7600 km and a mass of 3.5 × 1023 kg. A rock of mass 528 kg accelerates towards the planet from infinity.
Calculate the gravitational potential of the rock at a distance of 400 km above the planet's surface.
Step 1: Write the gravitational potential equationGraphical Representation of Gravitational Potential
Sketch a graph on the axes below to indicate how the gravitational potential varies with distance along a line outwards from the surface of planet A which is 80 times the mass of planet B.
The work done per unit positive charge in bringing a point test charge from infinity to a defined point
The electric field at a particular point is equal to the gradient of a potential-distance graph at that point
The rate of change of electric potential with respect to displacement in the direction of the field
The electric potential around a positive charge decreases with distance and increases with distance around a negative charge
The electric field strength E has a 1/r2 relationship
Drawing, interpreting or calculating from inverse square law graphs are common exam questions - there are lots of similarities between gravitational and electric field graphs:
Graphs of field strength against distance should start off steeper and decrease rapidly compared to that of potential graphs against distance, to distinguish it as an inverse square law (1/r2) relation instead of just an inverse relation (1/r)
There are plenty of differences too:
For example, gravitational potential always increases with respect to distance whereas electric potential can increase or decrease
One way to remember whether the electric potential increases or decreases with respect to the distance from the charge is by the direction of the electric field lines - the potential always decreases in the same direction as the field lines and vice versa.
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