https://www.khanacademy.org/science/highschool-physics/x6679aa2c65c01e53:motion-and-forces/x6679aa2c65c01e53:newtons-first-and-second-laws/v/newtons_first_law 2025-07-03T01:09:24.317391432Z Newton's first law Newton's first law states than an object at rest remains at rest, and an object in motion remains in motion with constant velocity, until acted on by an unbalanced force. The tendency of objects to maintain their state of motion is called inertia. On Earth, moving objects commonly come to rest without continued application of a force due to the unbalanced forces of friction and air resistance. Mahesh Shenoy video https://cdn.kastatic.org/ka_thumbnails_cache/1b446d2b-dde2-43fb-b2c6-c423050b1e00_1280_720_base.png Newton's first law Newton's first law states than an object at rest remains at rest, and an object in motion remains in motion with constant velocity, until acted on by an unbalanced force. The tendency of objects to maintain their state of motion is called inertia. On Earth, moving objects commonly come to rest without continued application of a force due to the unbalanced forces of friction and air resistance. https://cdn.kastatic.org/ka-youtube-converted/rjkQcfw5fkM.mp4/rjkQcfw5fkM.mp4 538 Newton's laws of motion https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:forces/x0e04e0cb682fb793:untitled-lesson-144newton-s-first-law-of-motion/a/what-is-newtons-first-law 2025-03-07T16:50:49.734868403Z What is Newton's first law? Also called the law of inertia, this is the most important thing to realize about motion. article https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:mass-weight-and-density/x0e04e0cb682fb793:mass-and-weight/a/what-is-weight 2025-02-28T00:12:11.735240474Z What is weight? Weight is another word for the force of gravity. article https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:forces/x0e04e0cb682fb793:newton-s-nd-law-of-motion/v/newtons_second_law 2024-06-30T23:53:54.560474813Z Newton's second law Newton's second law states than an object's acceleration is equal to the net force acting on the object, divided by its mass. Newton's first law is a special case of the second law when the net force on an object is zero. Newton's second law applies to macroscopic objects moving much slower than the speed of light. Mahesh Shenoy video https://cdn.kastatic.org/ka_thumbnails_cache/623858f6-5003-4ee9-96e9-197f9c6eb168_1280_720_base.png Newton's second law Newton's second law states than an object's acceleration is equal to the net force acting on the object, divided by its mass. Newton's first law is a special case of the second law when the net force on an object is zero. Newton's second law applies to macroscopic objects moving much slower than the speed of light. https://cdn.kastatic.org/ka-youtube-converted/EwGGh1dC3kQ.mp4/EwGGh1dC3kQ.mp4 684 Newton's laws of motion https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:forces/x0e04e0cb682fb793:newton-s-nd-law-of-motion/e/understand-newton-s-second-law 2026-06-20T14:19:59.261588707Z Understand: Newton's first and second laws Check your understanding of Newton's second law in this set of free practice questions. Emily Cizmas exercise https://www.khanacademy.org/science/cambridge-o-level-physics-cie/x0e04e0cb682fb793:forces/x0e04e0cb682fb793:newton-s-nd-law-of-motion/e/apply-newton-s-second-law 2026-01-23T20:00:36.154127952Z Apply: Newton's first and second laws Apply your knowledge of Newton's second law in this set of free practice questions. Emily Cizmas exercise https://www.khanacademy.org/science/ap-physics-c-mechanics/x077f5683c1428fac:force-and-translational-dynamics/x077f5683c1428fac:forces-and-acceleration/a/what-is-newtons-second-law 2026-05-01T14:10:52.97313295Z Learn and try: Newton's first and second laws Learn how to predict the translational motion of objects using Newton's first and second laws. article https://www.khanacademy.org/science/highschool-physics/x6679aa2c65c01e53:motion-and-forces/x6679aa2c65c01e53:newtons-first-and-second-laws/v/newtons_second_law_calculations 2024-07-01T11:54:52.194339821Z Newton's second law calculations Newton's second law can be used to calculate the acceleration that an object will experience, if the net force acting on the object and its mass are known. The law can also be used to determine the net force required to produce a certain acceleration for a known mass. Remember that the force term in Newton's second law refers to the net force on the object. Mahesh Shenoy video https://cdn.kastatic.org/ka_thumbnails_cache/2c25a321-d139-4a9b-b26c-a7f9a5ec0251_1280_720_base.png Newton's second law calculations Newton's second law can be used to calculate the acceleration that an object will experience, if the net force acting on the object and its mass are known. The law can also be used to determine the net force required to produce a certain acceleration for a known mass. Remember that the force term in Newton's second law refers to the net force on the object. https://cdn.kastatic.org/ka-youtube-converted/O5G4uHe-qc4.mp4/O5G4uHe-qc4.mp4 595 Newton's laws of motion https://www.khanacademy.org/science/highschool-physics/x6679aa2c65c01e53:motion-and-forces/x6679aa2c65c01e53:newtons-first-and-second-laws/e/apply-newton-s-second-law-calculations 2026-05-22T02:50:56.444203687Z Apply: Newton's second law calculations Apply your knowledge of Newton's second law calculations in this set of free practice questions. Emily Cizmas exercise https://www.khanacademy.org/science/in-in-class11th-physics/in-in-class11th-physics-laws-of-motion/in-in-class11-newtons-third-law/v/newton-s-third-law-of-motion 2023-04-30T21:01:15.828786566Z Newton's third law of motion Newton's third law states that for every action there is an equal and opposite reaction. The "action" and "reaction" refer to forces; if Object A exerts a force on Object B, then Object B exerts an equal amount of force on Object A in the opposite direction. Examples include pushing an object, stepping on the ground, and rockets. Sal Khan video https://cdn.kastatic.org/googleusercontent/Z6-bO4W7OJb9wSIOyD061O5-5nPNlcTxduwQL99ftRoES7Z8Ae2JbDHZ0y3Eb7BkGvedAzae1Y0PQJyx7OS-r9c Newton's third law of motion Newton's third law states that for every action there is an equal and opposite reaction. The "action" and "reaction" refer to forces; if Object A exerts a force on Object B, then Object B exerts an equal amount of force on Object A in the opposite direction. Examples include pushing an object, stepping on the ground, and rockets. https://cdn.kastatic.org/ka-youtube-converted/By-ggTfeuJU.mp4/By-ggTfeuJU.mp4 480 Newton's laws of motion https://www.khanacademy.org/science/in-in-class11th-physics/in-in-class11th-physics-laws-of-motion/in-in-class11-newtons-third-law/e/newton-s-third-law 2026-03-25T13:20:47.939559562Z Identifying equal and opposite forces Practice identifying the correct reaction to an action using Newton's third law.  Sean Boston exercise https://www.khanacademy.org/science/physics/forces-newtons-laws/newtons-laws-of-motion/v/more-on-newtons-third-law 2023-04-30T21:01:15.828786566Z More on Newton's third law Newton's third law states that objects exert equal and opposite forces on each other in every interaction. However, these forces do not cancel out because they act on two different objects. The magnitudes of the forces on both objects will be always be equal, but their resulting accelerations will not be equal if the objects have different masses. David SantoPietro video https://cdn.kastatic.org/googleusercontent/6U1crxkR7IThstBtIjjX6GEQ1kN7KtxHqaK4pF4B3NaemzOrPv1LoeWFLASk15ytuflAJCeTjcEkOubGICF4jzrbsA More on Newton's third law Newton's third law states that objects exert equal and opposite forces on each other in every interaction. However, these forces do not cancel out because they act on two different objects. The magnitudes of the forces on both objects will be always be equal, but their resulting accelerations will not be equal if the objects have different masses. https://cdn.kastatic.org/ka-youtube-converted/VfpKzwrhmqQ.mp4/VfpKzwrhmqQ.mp4 786 Newton's laws of motion https://www.khanacademy.org/science/in-in-class11th-physics/in-in-class11th-physics-laws-of-motion/in-in-class11-newtons-third-law/e/newtons-third-law 2026-03-25T13:20:47.939559562Z Newton's third law of motion Conceptual question testing understanding of Newton's Third Law of Motion Sal Khan exercise