MEDI 11002 Lecture Notes - Lecture 2: Gravitational Field, Net Force, Weightlessness
CHAPTER 2 – APPLYING FORCES
- Gravitation is a force of attraction that acts on all bodies
o The gravitational forces acts equally but oppositely on each of the two
bodies
o Isaac newton proposed an idea that the gravity from the earth acted
through space and exerted a force on the moon
o The gravitational force is directly related to their masses
o The gravitational force is weaker when the bodies are further apart.
There is an inverse square relationship between the force and the
distance of separation of the bodies
o The separation of the bodies is measured from the centre of mass of each
object
o Newton’s law of gravitation is:
This is the Law of Universal Gravitation and states: any two bodies
attract each other with a force which is proportional to the product of
their masses and inversely proportional to the square of their distance
apart
o The constant of universal gravitation is:
Terms to consider:
- Mass – the amount of matter in a body and is measured in kilograms. The mass
of a body does not vary with its position
- Weight – weight is a force and is measured in Newtons. The weight of an object
is the measure of the gravitational attraction between the earth and that object
- Centre of mass – single point in a body about which the mass is evenly
distributed. It is also the point at which objects will smoothly rotate
- Centre of gravity – the point at which all of the body’s weight may be
considered to act. In most cases it is the same point as the centre of mass
Gravitational fields and diagrams
- A gravitational field is a region in which any object with mass will experience a
force
- The gravitational field strength, is greater than around more massive central
objects, and becomes weaker at greater distances from the central body
- Gravitational field strength is given by:
o At the surface of the earth, the gravitational field strength is 9.8 N kg-1
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Document Summary
Gravitation is a force of attraction that acts on all bodies: the gravitational forces acts equally but oppositely on each of the two bodies object, the gravitational force is directly related to their masses. Mass the amount of matter in a body and is measured in kilograms. The mass of a body does not vary with its position. Weight weight is a force and is measured in newtons. The weight of an object is the measure of the gravitational attraction between the earth and that object. Centre of mass single point in a body about which the mass is evenly distributed. It is also the point at which objects will smoothly rotate. Centre of gravity the point at which all of the body"s weight may be considered to act. In most cases it is the same point as the centre of mass. A gravitational field is a region in which any object with mass will experience a force.
