# Chapter 7: Forces in Equilibrium

• Created by: Alice
• Created on: 05-04-13 15:24
• Chapter 7
• Vectors and Scalars
• A vector is any physical quantity that has a direction and magnitude
• A scalar is any physical quantity that is not directional e.g distance
• Balanced  Forces
• The combined effect of three forces  is only zero if the resultant of any two forces is equal and opposite to the third
• The principle of Moments
• Moment = F * d
• the sum of the clockwise moments = the sum of the anticlockwise moments
• The center of mass of a body is the point through which a single force on the body has not turning effect
• Moments (Extra)
• A couple is a pair of equal and opposite forces acting on a body
• The moment of a couple = torque
• Stablility
• Titling to occur: Fd > Wb/2
• If the line of action lies within the wheelbase = will not topple
• 1) Parallel to the slope F = W sin theta 2) Perpendicular to the slope Sx + Sy = Wcostheta
• Equilibrium Rules
• The triangle of forces have the vector sum F1 + F2 + F3 = 0
• A bpdy in eqilibrium acted on by three forces = libnes of actions must intersect at the same point
• For a body in equilibrium 1) the resultant force must be zero 2) the principle of moments must apply