Physics

• A force is a physical cause that changes or tends to change the state of rest or uniform motion of a body
• Effects of force on a body:

  • It can change the speed of a moving body
  • It can change the direction of motion of a moving body
  • It can make a body move or stop a moving body
  • It can change the shape and size of a body
• Contact forces act on bodies in direct contact, examples include frictional force, normal reaction force, tension force, collision force, and the force applied as a push or pull
• Noncontact forces act on bodies without being in contact, examples include gravitational force, electrical force, and magnetic force
• Magnitude of noncontact forces depends on the distance of separation of bodies, increasing as the separation decreases and vice versa
• SI unit of force is newton (N), where 1N is the force that acts on a body of mass 1kg and produces an acceleration of 1m/s^2 in the direction of the force
• CGS unit of force is dyne, where 1 dyne is the force that acts on a body of mass 1g and produces an acceleration of 1cm/s^2 in the direction of the force
• Gravitational units of force are kgf and gf, where 1 kgf = 1000 gf = 9.8 N and 1 gf = 980 dyne
• Frictional force opposes the relative motion between two surfaces in contact, arising due to the interlocking of irregular projections on the surfaces
• Types of frictional force: static friction, kinetic friction, and rolling friction
• Factors affecting force of friction:

  • Materials of bodies
  • Roughness of surfaces
  • Weights of bodies
• Disadvantages of friction:

  • Energy dissipates in the form of heat and sound
  • Causes wear and tear of machine parts
  • Reduces machine efficiency
  • May seize moving parts due to excessive heat
• Ways to reduce unwanted friction:

  • Using lubricants
  • Polishing
  • Using roller or ball bearings
  • Streamlining
• Advantages of friction:

  • Enables walking on roads or ground
  • Allows vehicles to run on roads
  • Helps in gripping, climbing, sitting, and writing
  • Essential for rotation of machine parts
  • Necessary for tying knots and holding objects
  • Important for billiard shots
• Friction can be increased by:

  • Making surfaces rough
  • Using dry surfaces
  • Increasing weight
• Translational motion is the motion of a body moving in a straight line in the direction of force
• Rotational motion occurs when a body is pivoted at a point and the applied force rotates it about a certain axis
• Turning force is the force applied at a point of a fixed body that rotates the body about the fixed point
• Moment of force or torque is the turning effect of a force acting on a body about an axis, measured as the product of force and the perpendicular distance from the axis of rotation
• SI unit of moment of force (torque) is newton metre (N m), and its CGS unit is dyne cm
• Principle of moments states that in equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments about any turning point
• Couple is formed by two equal and opposite parallel forces not acting along the same line, creating a turning effect called the moment of couple
• Centre of gravity is a point where the entire weight of a body is assumed to act, depending on the body's shape and mass distribution
• Uniform circular motion occurs when a body moves on a circular path with constant speed, under the action of a centripetal force directed towards the center of the circle
• Centrifugal force is an apparent force that acts outwards on a body moving about a center, caused by the body's inertia and assumed equal and opposite to the centripetal force
• Work is done when a force produces a displacement of a body
• The amount of work done by a force is equal to the product of the force and the displacement of the point of application of the force in the direction of force
• If there is no motion produced in the body even if a force acts on it, the work done is zero
• If a force F acts on a body and displaces it at an angle θ to the direction of force, then:

  • Work done = Force × Component of displacement in the direction of force
• Work done by the force of gravity is W = mgh, where m = mass, g = acceleration due to gravity, and h = height from the earth's surface
• Work is a scalar quantity and the SI unit of work is joule (J)
• Power is the rate of doing work
• Power is measured as the amount of work done in one second
• Power is a scalar quantity and the SI unit of power is watt (W)
• Energy is the capacity of a body to do work
• The SI unit of energy is joule and its CGS unit is erg
• Kinetic energy is the energy possessed by a body due to its state of motion
• Potential energy is the energy possessed by a body due to its position or configuration
• The law of conservation of mechanical energy states that potential energy is equal to kinetic energy
• Different types of energy include:

  • Heat energy
  • Chemical energy
  • Light energy
  • Sound energy
  • Magnetic energy
  • Electrical energy
  • Nuclear energy
  • Geothermal energy
  • Hydroelectricity
  • Tidal energy
  • Kinetic energy
  • Biomass energy