Forces

• The four fundamental interactions in the universe are:

  • Gravitational Force
  • Electromagnetic Force
  • Strong Nuclear Force
  • Weak Nuclear Force
• Force is defined as the rate of change of momentum of an object which is free to move. The direction of the force is in the direction of change in momentum.
• A force is conservative if the work it does on an object moving between two points is independent of the path the object takes.
• A force is non-conservative if the work it does on an object depends on the path taken by the object between its initial and final points.
• Non-contact forces include:

  • Gravitational force
  • Electric force
  • Magnetic force
• Contact forces include:

  • Normal Reaction force
  • Friction force
  • Tension force
• Friction and drag force are known as dissipative forces as objects that experiences these forces would have their energy dissipated as heat to the surroundings.
• Frictional force is the force exerted by one body on another body when two bodies slide over one another.
• Drag force is the frictional force experienced either by an object as it moves through a fluid or by a fluid as it moves over a surface.
• The magnitude of the drag force increases with increase in speed of the object.
• The entire weight of a body may be taken as acting at a single point known as its centre of gravity.
• The centre of gravity of a homogenous, symmetric body must lie on its axis of symmetry.
• Hooke's Law states that force is directly proportional to the extension of a spring, provided that the elastic limit has not been reached.
• By Hooke's Law,

  F = k * x
• Elastic potential energy is the energy stored in a body due to its elastic deformation.
• Elastic potential energy is equal to the area under the force-extension curve.

  
• Upthrust is the vertical upward force exerted by the surrounding fluid when a body is submerged partially or fully in a fluid. It is equal in magnitude and opposite in direction to the weight of the fluid displaced by the body.
• Upthrust is the resultant force due to the difference in pressure exerted by the fluid at the top and bottom surfaces of the body.
• $P =$$\frac{F}{A}$ (in units)


  P = Pa

  F = N

  A = m^2
• $U=$$m_fg$ (by name)


  U = Upthrust force

  $m_f$= Mass of fluid displaced

  g = Acceleration of free fall
• Archimedes' Principle states that for any object immersed partially or fully in a fluid, the upthrust is equal in magnitude and opposite in direction to the weight of fluid displaced by the object.
• Principle of Floatation states that when an object is floating in equilibrium in a fluid, the weight of the object is equal to the weight of fluid displaced by the object.
• When a body is in equilibrium,

  • Resultant force on it must be zero in any direction
  • Resultant torque on it must be zero about any axis of rotation
• Translational equilibrium occurs when resultant force on a body is zero in any direction.
• Rotational equilibrium occurs when resultant torque on a body is zero about any axis of rotation.
• The moment of a force about a pivot is the product of the magnitude of the force and the perpendicular distance of the force from the pivot.
• The torque of a couple is the product of one of the forces and the perpendicular distance between the forces.
• A couple consists of a pair of forces of equal magnitude but acting in opposite directions whose line of action are parallel but separate.
• The Principle of Moments states that when a system is in equilibrium, the sum of clockwise moments about any axis must be equal to the sum of anticlockwise moments about the same axis.
• The elastic limit is defined as the point beyond which the spring does not return to its original length when the load is removed.
• Hydrostatic pressure is the pressure at a certain depth or at a point in the liquid.
• $\rho=$$\frac{m}{V}$ (by name)


  $\rho$ = Density

  m = Mass

  V = Volume
• What is a region of space where a force is felt?

  Field of Force
• Tensile forces is defined as two forces acting in opposite directions on an object so as to tend to increase its length along the direction of the forces.
• Compressive forces is defined as two forces acting in opposite directions on an object so as to tend to reduce its length along the direction of the forces.
• The centre of mass is the mean location of all the mass in a system. It is the point through which a single force must act for the object to accelerate linearly without rotation.
• Terminal velocity is the constant velocity achieved by an object when it is falling under gravity through a viscous fluid.