Force and Laws of Motion

• Force enables us to do work by either pulling or pushing an object
• Force can make a stationary body move, stop a moving body, change the direction of a moving object, change the speed of a moving body, and change the shape and size of an object
• Forces are mainly of two types: balanced forces and unbalanced forces
• Balanced forces have a resultant of zero and do not cause any change of state of an object
• Balanced forces can change the shape and size of an object
• Unbalanced forces have a resultant greater than zero and can move a stationary object, increase or decrease the speed of a moving object, stop a moving object, and change the shape and size of an object
• Galileo Galilei stated that objects move with a constant speed when no forces act on them, but practically, this is not possible due to forces like friction and air resistance
• Newton's Laws of Motion:

  • Newton's First Law of Motion (Law of Inertia) states that an object remains at rest or in uniform motion along a straight line unless acted upon by an external force
  • Examples of Newton's First Law of Motion in everyday life
• Inertia is the property of an object that resists changes in its state of motion or rest and is measured by its mass
• Momentum is the power of motion of an object and is the product of velocity and mass (p = m × v)
• Examples to understand momentum:

  • A person gets injured when hit by a moving object due to the object's momentum
  • Even a small bullet can kill a person due to its momentum from great velocity
  • A person gets severely injured when hit by a moving vehicle due to the vehicle's momentum from mass and velocity
• Momentum of an object in the state of rest is equal to zero
• SI unit of momentum is kgm/s
• Momentum = mass × velocity
• Second Law of Motion:

  • Rate of change of momentum of an object is proportional to applied unbalanced force in the direction of force
• Third Law of Motion:

  • For every action there is an equal and opposite reaction
• Law of Conservation of Momentum:

  • When two (or more) bodies act upon one another, their total momentum remains constant provided no external forces are acting