P8: Forces in Balance

• Force

  A push or pull acting on an object due to interaction with another object
• Resultant Force

  The single force that has the same effect as all the original forces acting together
• Equilibrium

  When the resultant force on an object is zero, so the object remains at rest or continues to move with constant velocity
• Resolution of Forces

  Breaking a single force into components acting in different directions
• Vector

  A quantity that has both magnitude and direction
• Scalar

  A quantity that has only magnitude and no direction
• Newton's First Law of Motion

  • An object will remain at rest or continue to move at a constant velocity unless acted upon by an external force
• Newton's Second Law of Motion

  • The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass
• Newton's Third Law of Motion

  • For every action, there is an equal and opposite reaction
• Weight

  The force acting on an object due to gravity
• Normal Reaction Force

  The force exerted by a surface that supports the weight of an object resting on it
• Tension

  The force transmitted through a string, rope, cable, or similar object when it is pulled tight by forces acting from opposite ends
• Frictional Force

  The force resisting the relative motion of solid surfaces, fluid layers, or material elements sliding against each other
• Coefficient of Friction

  A dimensionless scalar value that shows the ratio of the force of friction between two bodies and the force pressing them together
• Centre of Mass

  The point at which the entire mass of an object can be considered to be concentrated
• Moments

  The turning effect of a force around a pivot or fulcrum
• Principle of Moments

  • For an object in equilibrium, the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about the same point
• Couple

  A pair of equal and opposite forces acting on a body but not along the same line
• Centre of Gravity

  The point where the entire weight of an object can be considered to act
• Stability

  The ability of an object to return to its original position after being disturbed