- the law of action & reaction - for every action, there is an equal & opposite reaction - when one object exerts a force on another object, the second object will also exert an equal force in the opposite direction - Newton's third law focuses on separate objects & their forces (action & reaction), not just a single object like in [[Equilibrium]] ![[CleanShot 2024-06-02 at 17.56.41.png|400]] ![[CleanShot 2024-06-02 at 17.51.07.png|400]] - when you lower tennis ball, it feels lighter momentarily, because the opposite force has briefly become lighter (you exert less force on the ball) ![[CleanShot 2024-06-02 at 18.13.00.png|400]] - conversely, it will feel heavier momentarily when you move hand up (opposite force becomes greater) - while you are moving, you must exert a force more than gravity, but once you reach peak you can lower the upward exerted force to exactly gravity again - note to move ball upwards, you have to exert a force on the ball greater than the natural downward force of gravity - that's the only way to have the resultant force move it up ![[CleanShot 2024-06-02 at 18.15.33.png|400]] - personal observation: - gravity & your hand holding up the ball so it doesn't fall are forces that act on the ball, & keep it static - however, when you lift your hand to hold it up to enact that upward force on the ball, the 3rd law comes into play by enacting the equal opposite force on your hand - NOT the ball