Weight and Mass
Mass is the amount of matter in an object; it never changes with location.
Weight is the gravitational force on an object: W=m×gW =
Unit of weight → Newton (N); unit of mass → kilogram (kg).
Weight changes with gravity; mass does not.
Gravity
Gravity is the force of attraction between all objects with mass.
On Earth, average = 9.8m/s
It varies slightly (9.78 at equator, 9.83 at poles).
Gravity decreases with height and distance from Earth’s center.
Acts toward the center of the Earth, because all mass pulls equally inward.
Responsible for keeping planets in orbit and objects grounded.
Unit of Gravity
SI unit: m/s²
velocity increases by 9.8 m/s every second during free fall on Earth.
Variation of Weight
Weight is maximum at poles and minimum at equator.
Decreases with altitude and when moving away from Earth.
Slightly affected by Earth’s rotation and shape.
Types of Forces
Contact Forces
Frictional – opposes motion between surfaces.
Normal – support force from a surface.
Tension – in stretched ropes or strings.
Spring – in stretched or compressed springs.
Applied – push or pull by an external agent.
Air Resistance – opposes motion through air.