force physics

• Force


  F = ma (mass m is constant)
• Force


  • F = mv
  • F = mp
• Newton's second law of motion states that F = ma
• Linear motion


  Motion of an object in a straight line
• Rotational motion


  Motion of a body that rotates about a fixed axis or point
• The motion of a door when a force is applied on its handle is rotational motion
• Moment of force


  The product of the magnitude of the force applied and the perpendicular distance of the line of action of the force from the axis of rotation
• The moment of force depends on both the magnitude of the force and its perpendicular distance from the axis
• To produce the maximum turning effect, the perpendicular distance of the line of force from the axis of rotation should be maximum
• 10^7 dyne cm is equal to 1 Nm
• The direction of rotation of a pivoted body can be changed by changing the direction of force and the point of application of force
• Couple


  Two equal and opposite parallel forces not acting along the same line
• According to the principle of moments in equilibrium, the sum of anticlockwise moments is equal to the sum of clockwise moments
• When a body is acted upon by two unequal forces in opposite directions, but not in the same line, the body will have rotational as well as translational motion
• Examples of dynamic equilibrium

  • Moon revolving around the earth
  • A pebble fixed at the end of a string whirling in a circular path
  • An aeroplane moving at a constant height
• Translational motion is produced when a body is free to move
• Rotational motion is produced when the body is fixed at a point
• The moment of force is a vector quantity
• The moment of force can be reduced by decreasing the perpendicular distance of force from the axis of rotation
• The moment of force can be increased by increasing the perpendicular distance of force from the axis of rotation
• Completed sentences


  • The S.I. unit of moment of force is Newton metre (Nm)
  • In equilibrium, the algebraic sum of moments of all forces about the point of rotation is zero
  • In a beam balance when the beam is balanced in a horizontal position, it is in static equilibrium
  • The moon revolving around the earth is in dynamic equilibrium
• Factors affecting the turning effect of a force

  • The magnitude of the force applied
  • The distance of the line of action of the force from the axis of rotation
• The direction of rotation can be changed by changing the direction of force
• It is easier to open a door by applying the force at the free end because the perpendicular distance is larger, requiring less force to turn the body
• The stone of a hand flour grinder is provided with a handle near its rim so that by applying small force at the handle it can be rotated easily about the fixed point at its centre
• It is easier to turn the steering wheel of a large diameter in comparison to the wheel of a smaller diameter as less force is required in the first case due to the larger distance from the centre of the rim
• A spanner is provided with a long handle so as to create a larger turning moment with less force
• A jack screw which is used to lift a heavy vehicle has a long arm so that less force is needed to rotate it to raise or lower the vehicle
• If a heavy roller with its axle at O is to be raised on a pavement XY, the force should be applied as shown in the diagram, but if pivoted at O, it will not go up
• Moment of couple


  The product of either force and the perpendicular distance between the two forces
• Spanner (or wrench)


  A tool with a long handle
• Jack screw


  A tool used to lift heavy vehicles, with a long arm
• A jack screw has a long arm so that less force is needed to rotate it to raise or lower the vehicle
• If a heavy roller with its axle at O is to be raised on a pavement XY, and there is friction between the roller and pavement, the point of application and direction of force to be applied is shown in the diagram. If pivoted at O, it will not go up
• Moment of a couple


  The product of either force and the perpendicular distance between the two forces
• Equilibrium of a body

  When a number of forces acting on a body produce no change in its state of rest or of linear or rotational motion
• Static equilibrium


  When a body remains in the state of rest under the influence of several forces
• Static equilibrium


  • A toy lying on a floor
• Dynamic equilibrium


  When a body remains in the same state of motion (translation or rotational), under the influence of several forces
• Dynamic equilibrium


  • An apple falling from a tree with a constant velocity