GRAVITY

Gravitational force - the attractive force possessed by all objects with mass, which exerts a pull on all other objects with mass

SI unit is Newtons (N)

Gravitational acceleration - the acceleration of an object in freefall in a vacuum, caused by gravitational force (can be used interchangeably with gravitational field strength)

Gravitational force is one of the four fundamental forces; it acts on a distance, without requiring direct contact. It causes objects to have weight and pulls all masses towards the center of mass of the source of the gravitational force. All objects with mass exert gravitational force on all other masses within their gravitational field.

Newton’s law of universal gravitation states that the force of gravity is directly proportional to the products of the masses in question, and inversely proportional to the square of the distance between the masses.

Weight - the product of an object's mass and the gravitational force being exerted on it

can be quantified with W = mg
- W - weight (N)
- m - mass (kg)
- g - gravitational acceleration (m/s^2)

The equation for weight allows for the assumption that the greater the mass of an object, the greater its weight would be.

If an object is resting on a table (or any other surface), two forces act on the object - the force of gravity pulling the object down, and the resulting normal force which is directly opposite to gravity.

GRAVITATIONAL FIELDS

Gravitational field - a field in which an object with mass experiences gravitational force; all objects with mass have a gravitational field

Gravitational fields spread in all directions, but the force of the field decreases as the distance from the object at its center increases.

Gravitational field strength - the gravitational force exerted on an object per unit mass (used interchangeably with gravitational acceleration); gravitational field strength increases as you get closer to the center of mass of the object producing the field

Earth's gravitational field strength is 9.8 m/s^2 (can be rounded up to 10)
the product of gravitational field strength and the total mass of an object is another way of calculating gravitational force

The gravitational acceleration acting on all objects in a field will be the same regardless of their masses - the mass determines the magnitude of the overall force being experienced by the object rather than its velocity. However, gravitational acceleration around a body varies depending on distance from the center of its mass. Such distances would only be significant if they were on an astronomical scale, but on and around the surface of most large/massive objects, the differences in the varying distance from their center of mass are negligible. Therefore, gravitational field strength on the surface of most massive bodies is assumed to remain constant.

Due to Newton's law of universal gravitation, mass is also a key factor in gravitational fields; the force between two pens would be much less significant than the force between the pen and the Earth. Because the Earth is much more massive, it has an enormous gravitational field compared to the gravitational field of the pen. This is essentially how all bodies in our solar system stay in orbit around the sun - because of its huge gravitational field.