Term
Describe the force of gravity. 

Definition
The force of gravity is an attractive force acting between any 2 objects due to their masses. 


Term
Q1)What is a gravitational field? Q2)What is the strength of a gravitational field at a point? Q3) What do field lines tell us about a field? 

Definition
A1) A region in which an object with mass will feel a force. A2)The strength of the field at a point is the force exerted per unit mass placed in the field. A3) The arrows on the field lines show the direction of the force of a mass placed in the field. The spacing of the lines shows the strength of the field. i.e. the farther apart the field lines, the weaker the field. 


Term
What is the difference between the field of a uniform spherical mass and the field of an equal point mass at the centre of the sphere? 

Definition
There is no difference. The fields are the same. 


Term
What is Newton's law of gravitation? 

Definition
Any two point masses attract each other with a force that is proportional to each of their masses and inversly proportional to the square of the distance between them. The force between 2 point masses: F=Gm_{1}m_{2} /r^{2} G=6.67x10^{11}Nm^{2}Kg^{2} 


Term
What is the field strength at distance r from point mass M given by? 

Definition
g=GM/r^{2 } because F=gm and F=GMm/r^{2 } so gm=GMm/r^{2} so g=GMm/r^{2}m



Term
Q1)On or near the surface of the earth, how would you describe the field? Q2) What is the gravitational field strength equal to? 

Definition
A1) On or near the surface of the earth, the field is uniform.[image]
A2) g is equal to the acceleration of free fall. 

