Kireeti Gudipalli

gravitational field at a point is the force experienced by a unit mass placed at that point. Its direction is  towards the center of the mass causing the gravitational field.  units are newtons per kilogram (N/kg) in the International System of Units (SI)

it is a vector quantity

Gravitational potential

It is defined as the amount of work done to move an object from a reference point (often infinity) to a specific point in the gravitational field

it is a scalar quantity 

• Friction is a force that opposes the relative motion or tendency of such motion of two surfaces in contact
• types of friction
• Static friction-This type of friction occurs when there is no relative motion between the surfaces in contact. It prevents an object from starting to move when a force is applied to it parallel to the surface.
• Sliding friction-Kinetic friction occurs between surfaces in motion relative to each other. Once an object overcomes static friction and starts moving, kinetic friction opposes its motion.
• Rolling friction-Rolling friction occurs when an object rolls over a surface. It's generally lower than sliding friction because rolling involves less contact area and deformation of the surfaces