বলের ধারণা ও প্রকারভেদ

• Force is a fundamental concept in physics that describes an interaction that, when unopposed, will change the motion of an object
• A force can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate
• Force can be described intuitively as a push or a pull
• Force is a vector quantity, meaning it has both magnitude and direction
• It is measured in the SI unit of newtons (N)
• Force is represented by the symbol F

Types of Forces

• Contact Forces: These forces result from direct physical contact between objects
  • Applied Force: A force applied to an object by another object
  • Frictional Force: A force that opposes motion when two surfaces rub against each other
  • Tension Force: The force transmitted through a string, rope, cable, or wire when it is pulled tight by forces acting from opposite ends
  • Normal Force: The force exerted by a surface on an object in contact with it, perpendicular to the surface
  • Air Resistance Force: A force that opposes the motion of objects through the air
  • Spring Force: The force exerted by a compressed or stretched spring upon any object that is attached to it
• Non-Contact Forces (Action at a Distance Forces): These forces can act between objects that are not in physical contact
  • Gravitational Force: The force of attraction between objects with mass
  • Electric Force: The force between electrically charged objects
  • Magnetic Force: The force between magnetic objects

Newton's Laws of Motion

• Newton's Laws of Motion are three physical laws that describe the relationship between a body and the forces acting upon it, and its motion in response to those forces
• First Law (Law of Inertia): An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by a force
  • Inertia is the tendency of an object to resist changes in its state of motion
  • Mass is a measure of an object's inertia
• Second Law: The acceleration of an object is directly proportional to the net force acting on the object, is in the same direction as the net force, and is inversely proportional to the mass of the object (F = ma)
  • F is the net force acting on the object
  • m is the mass of the object
  • a is the acceleration of the object
• Third Law: For every action, there is an equal and opposite reaction
  • If object A exerts a force on object B, then object B exerts an equal and opposite force on object A

Net Force

• Net force is the vector sum of all the forces acting on an object
• It is the total force that affects the object's motion
• If the net force on an object is zero, the object is said to be in equilibrium (either at rest or moving with constant velocity)
• When forces are in the same direction, their magnitudes are added
• When forces are in opposite directions, their magnitudes are subtracted
• When forces are at angles to each other, vector addition is used to find the net force

Free-Body Diagrams

• A free-body diagram (FBD) is a visual representation of all the forces acting on an object
• It is a simplified diagram that shows the object as a point and the forces as vectors originating from that point
• FBDs are used to analyze the forces acting on an object and to apply Newton's Second Law to solve for unknown quantities

Units of Force

• The SI unit of force is the newton (N)
  • 1 N is the force required to accelerate a 1 kg mass at a rate of 1 m/s² (1 N = 1 kg * m/s²)
• In the Imperial system, the unit of force is the pound (lb)

Gravitational Force and Weight

• Gravitational force is the attractive force between objects with mass
• The gravitational force between two objects is proportional to the product of their masses and inversely proportional to the square of the distance between their centers
• Weight is the force of gravity acting on an object
• Weight (W) = mg, where m is the mass of the object and g is the acceleration due to gravity
• On Earth, g is approximately 9.8 m/s²

Friction

• Friction is a force that opposes motion between surfaces in contact
• Static Friction: The force that prevents an object from starting to move when a force is applied
  • It is equal in magnitude and opposite in direction to the applied force, up to a maximum value
• Kinetic Friction: The force that opposes the motion of an object that is already moving
  • It is generally less than the maximum static friction force
• The friction force is proportional to the normal force between the surfaces
• Frictional force (Ff) = μN, where μ is the coefficient of friction (static or kinetic) and N is the normal force

Tension

• Tension is the force transmitted through a string, rope, cable, or wire when it is pulled tight by forces acting from opposite ends
• Tension is a pulling force and acts along the length of the string or rope
• In an ideal (massless and unstretchable) string, the tension is the same at all points along the string

Applied Force

• An applied force is a force that is directly applied to an object by another object
• The direction of the applied force is the direction in which the object is being pushed or pulled

Air Resistance

• Air resistance is a force that opposes the motion of an object through the air
• It is caused by the collision of the object with air molecules
• Air resistance depends on the object's speed, shape, and size, as well as the density of the air
• At high speeds, air resistance can become a significant force

Spring Force

• Spring force is the force exerted by a compressed or stretched spring on any object attached to it
• It is described by Hooke's Law: F = -kx, where F is the spring force, k is the spring constant (a measure of the spring's stiffness), and x is the displacement of the spring from its equilibrium position
• The negative sign indicates that the spring force is a restoring force, meaning it acts in the opposite direction to the displacement