Quiz 5

• gravitational field strength


  A point in a gravitational field is the gravitational force per unit mass experienced by a body at that point.
• uniform (gravitational) fields


  The direction and strength of the field is constant throughout the considered region of space, (e.g. to a good approximation the gravitational field on the surface of the Earth is uniform when distances considered are small relative to the Earth’s radius (6400 km)).
• geostationary orbit


  An orbit with a period of 24 hours. Orbiting body is above the equator and rotates around the Earth’s centre of mass in the same sense as the Earth does, leading to the satellite remaining in a fixed position above a given point on the Earth’s surface.
• newton's law of gravitation


  The force of attraction between two given particles is inversely proportional to the square of their separation and directly proportional to the product of their masses, (and acts along a line joining their centres of mass).
• couple


  “A pair of equal and opposite force (with their lines of action separated by a distance)”
• principle of conservation of energy


  “Energy cannot be created or destroyed; it can only be transferred” “The total energy (of a system) remains constant”
• line of action of a force


  A straight line parallel to the force considered and passing through the point of application of the force, (i.e. the point where the force acts on the extended body).
• moment of a force

  “Moment = force x perpendicular distance from pivot/point”
• centre of gravity


  The point where the weight (appears) to act.
• condition for mechanical equilibrium


  Net force = 0 and Net moment = 0