rigid bodies Flashcards
(9 cards)
rigid bodies take into account…
rotation of the body, size of the object
moments in equilibrium
clockwise moment = anti-clockwise
what is the moment of a force
measures the turning effect of the force on the body on which it is acting
moment of a force =
force x distance ( PERPENDICULAR DISTANCE)
if a rigid body is in equilibrium,
- the resultant force in any direction = 0 , so forces up = forces down (y1)
- the resultant moment about any point is 0 ( clockwise moment = anti-clockwise moment)
what does uniform mean?
where does weight act on a uniform body
- mass spread evenly
- weight acts on the centre
when a rigid body is on the point of tilting about a pivot…
the reaction at any other support, or tension in any other wire/string, is zero
when to use R and mew R or X and Y
🧱 1. When to Use “R” and “μR”
You use R and μR when dealing with contact forces between surfaces — like a rod resting on a rough or smooth floor, wall, or peg.
R = Normal Reaction Force (acts perpendicular to the surface)
μR = Friction Force (acts parallel to the surface, max value is μR)
Example:
A uniform ladder leans against a rough wall:
The wall provides a horizontal reaction R₁ (could be friction or normal).
The ground gives a vertical reaction R₂, and a horizontal friction μR₂ (if rough).
🧭 2. When to Use “X” and “Y”
Use X and Y when you’re resolving a general unknown force into components. This is usually:
A tension, pull, or diagonal force at an angle.
Something that doesn’t involve normal contact with a surface.
You’re saying:
“I don’t know exactly what this force is, but I can break it into:
A horizontal component (X = F cosθ)
A vertical component (Y = F sinθ)”
if a rope is not modelled as light, how would that affect the tension along the rope
the tension in the rope will not be constant throughout its length , because ropes own weight will contribute to the tension
