Forces in Action

• When a resultant force 'F' acts on a body with mass, the body will accelerate in the direction of the resultant force. Resultant force is related to mass and acceleration by the formula

  F = ma
• Common forces and explanation:

  • Weight - the gravitational force acting on an object through it's center of mass
  • Friction - the force that arises when two surfaces rub against each other.
  • Drag - The resistive force on an object travelling through a fluid (water, air)
  • Tension - the force within a stretched cable or rope
  • Upthrust -the upward force acting on an object when it is in a fluid
  • Normal contact force - the force arising when an object rests against another object.
• Terminal velocity is when the forces acting on the falling object become balanced so the resultant force is 0, acceleration becomes 0
• Principle of moments is for an object in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments
• A moment is the turning effect of a force about some axis or point.
• A couple is a pair of equal and opposite forces that have a equal magnitude in opposite direction
• Density is the mass per unit volume of a substance.

  P = M / V Unit is kgm^-3
• Pressure is the normal force exerted on a surface per unit area, it is measured in Nm or Pascals.

  1Pa = 1Nm
• The force that an object submerged in a fluid experiences an upwards force called upthrust, because the pressure at the bottom surface of the object is greater than at it's top surface
• Archimedes principle states that the upthrust exerted on a body immersed in fluid, weather partially or submerged is equal to the weight of the fluid that the body displaces

  An object will sink if the upthrust is smaller than the weight.
• Weight of an object is defined as the gravitational force acting upon the object through its centre of mass
• One newton is defined as the force that will give a mass of 1kg an acceleration of 1
• Drag is a frictional force that opposes motion and its magnitude depends on speed, shape and texture of the object
• Terminal velocity is when drag equals thrust so there is no net force acting on the object
• centre of mass of an object is the point where the entire weight of the object appears to act