{"id":10234,"date":"2026-07-03T17:39:42","date_gmt":"2026-07-03T17:39:42","guid":{"rendered":"https:\/\/kapdec.com\/help\/?p=10234"},"modified":"2026-07-03T17:39:42","modified_gmt":"2026-07-03T17:39:42","slug":"newton-laws","status":"publish","type":"post","link":"https:\/\/kapdec.com\/help\/newton-laws\/","title":{"rendered":"Newton Laws"},"content":{"rendered":"
\n
\n

KAPDEC® | Elite STEM Learning Platform | https:\/\/kapdec.com<\/a><\/p>\n

\n

Unit: <\/strong>Dynamics<\/strong><\/h2>\n

Chapter: <\/strong>Newton\u2019s laws<\/strong><\/h3>\n

Reference: AP Physics Algebra, <\/em>Dynamics, <\/em>Newton\u2019s laws, <\/em>Force, Newton\u2019s First Law of Motion, Concept of Momentum, Newton\u2019s Second Law of Motion, Newton\u2019s Third Law of Motion<\/em><\/p>\n

After studying this chapter, you should be able to:<\/strong><\/p>\n

    \n
  • state Newton\u2019s laws<\/li>\n
  • solve the problem related to Newton\u2019s laws<\/li>\n<\/ul>\n

    Force:<\/strong><\/p>\n

    A force is a push or pull acting on a body. It is a vector quantity i.e.; it has both magnitude and direction.<\/p>\n

    Unit of Force: <\/strong>Its unit is Newton in the SI system and Dyne in the CGS system.<\/p>\n

    Dimension<\/strong>: MLT <\/sub>–<\/sup>2<\/sup><\/p>\n

    \u00a0(a)Contact Forces:<\/strong> Tension, Normal Reaction, Friction etc. Forces that act between bodies in contact.<\/p>\n

    (b)Field forces (non-contact forces):<\/strong> Weight, electrostatic forces, etc.\u00a0 Forces that act between bodies separated by a distance without any actual contact.<\/p>\n

    Newton\u2019s First Law of Motion:<\/strong><\/p>\n

    Isaac Newton generalized Galileo\u2019s conclusions in the form of a law known as Newton\u2019s first law of motion, which states that a body continues to be in a state of rest or of uniform motion in a straight line unless it is acted upon by a net external force.<\/p>\n

    The first law, also known as the law of inertia, states that an object at rest will remain at rest, and an object in motion will continue to move in a straight line at a constant speed unless acted upon by an external force. In other words, objects tend to resist changes in their state of motion.<\/strong><\/p>\n

    Concept of Momentum<\/strong><\/p>\n

    You must have seen that a fielder finds it difficult to stop a cricket ball moving with a large velocity although its mass is small. Similarly, it is difficult to stop a truck from moving with a small velocity because its mass is large. These examples suggest that both, the mass and velocity of a body, are important when we study the effect of force on the motion of the body. The product of mass m of a body and its velocity v is called its linear momentum p. Mathematically,<\/p>\n

    \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 we, write p = mv<\/strong><\/p>\n

    In SI units, momentum is measured in kg ms\u20131<\/sup>. Momentum is a vector quantity. The direction of the momentum vector is the same as the direction of the velocity vector. The momentum of an object, therefore, can change on account of a change in its magnitude or direction or both. The following examples illustrate this point.<\/p>\n

    \u00a0<\/p>\n

    Newton\u2019s Second Law of Motion:<\/strong><\/p>\n

    Newton\u2019s second law states that the rate of change of momentum of a body is directly proportional to the applied force.<\/p>\n

    \"\"<\/p>\n

    Source: Kapdec.com<\/p>\n<\/div>\n

    \u00a0<\/p>\n

    Where k is the constant of proportionality.<\/p>\n

    Unit force is now defined as that force which produces a unit rate of change of momentum in a body<\/p>\n

    \u00a0<\/p>\n

    \"\"<\/p>\n

    Source: Kapdec.com<\/p>\n<\/div>\n

    Note that the second law of motion gives us a unit for measuring force. The SI unit of force i.e., a newton may thus, be defined as the force which will produce an acceleration of 1 ms\u20132<\/sup> in a mass of 1 kg.<\/p>\n

    Newton\u2019s Third Law of Motion:<\/strong><\/p>\n

    The third law states that for every action, there is an equal and opposite reaction. This means that whenever one object exerts a force on another object, the second object exerts an equal and opposite force back on the first object. Every action has an equal and opposite reaction<\/p>\n

    If F12<\/sub> is the force which object 1 experiences due to object 2 and F21<\/sub> is the force which object 2 experiences due to object 1, then according to Newton\u2019s third law of motion, we can write<\/p>\n

    \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 F12<\/sub> = \u2013F21<\/sub><\/p>\n

    Example 1:\u00a0 A block of mass m = 10 kg is pulled by a force F = 100 N at an angle q = 30o<\/sup> with the horizontal along a smooth horizontal surface. What is the acceleration of the block? (g = 10 m\/s2<\/sup>)<\/em><\/p>\n

    \u00a0<\/p>\n

    \u00a0<\/p>\n

    \"\"<\/p>\n

    Source: Kapdec.com<\/p>\n<\/div>\n

    \u00a0<\/p>\n

    Solution:<\/strong>\u00a0\u00a0 The forces that act on the body can be decomposed along x and y axis.<\/p>\n

    As there is no acceleration along y-axis, the net force acting along the vertical or y-axis should be zero i.e.<\/p>\n

    \u00a0 \u00e5FY<\/sub> = N + Fsinq \u2013 mg = 0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 . . . (1)<\/em><\/p>\n

    \u00a0The body accelerates along the x-axis. Therefore\u00a0 \u00a0 \u00a0 \u00a0<\/em><\/p>\n

    \u00a0 \u00a0 \u00a0 \u00a0 The acceleration of the block is 53\u2004m\/s2<\/sup><\/em><\/p>\n

    Directed towards right. Since F sinq < mg & the surface is rigid, the block remains in equilibrium along y-axis.<\/em><\/p>\n

    \u00a0<\/p>\n

    \u00a0<\/p>\n

    Key points:<\/strong><\/p>\n

    \u00a0<\/p>\n

    Isaac Newton’s laws of motion are the foundation of classical mechanics and describe the behaviour of objects in motion. They are as follows:<\/p>\n

      \n
    • The first law, also known as the law of inertia, states that an object at rest will remain at rest, and an object in motion will continue to move in a straight line at a constant speed unless acted upon by an external force. In other words, objects tend to resist changes in their state of motion.<\/li>\n
    • The second law states that the force applied to an object is directly proportional to its mass and acceleration. This law is expressed mathematically as F=ma, where F is the force, m is the mass of the object, and a is the acceleration.<\/li>\n
    • The third law states that for every action, there is an equal and opposite reaction. This means that whenever one object exerts a force on another object, the second object exerts an equal and opposite force back on the first object.<\/li>\n<\/ul>\n

      \u00a0<\/p>\n

      Together, these laws provide a framework for understanding the motion of objects and the forces that affect them.<\/p>\n

      \u00a0<\/p>\n

      <\/p>\n