Newton’s Second Law Physical Science 3.1

Force and Acceleration Greater force = greater acceleration Greater force = greater acceleration Applying force causes change in velocity Applying force causes change in velocity Velocity change over a shorter period of time = more acceleration change Velocity change over a shorter period of time = more acceleration change Same force on different object may result in different acceleration Same force on different object may result in different acceleration More mass = less acceleration More mass = less acceleration Newton’s 2 nd law: The net force acting on an object causes the object to accelerate in the direction of the net force Newton’s 2 nd law: The net force acting on an object causes the object to accelerate in the direction of the net force a = F/m a = F/m

Force and Acceleration Units Units Mass: kg Mass: kg Acceleration: m/s 2 Acceleration: m/s 2 Force: N = kg*m/s 2 Force: N = kg*m/s 2 a = F/m also written as F = ma a = F/m also written as F = ma Friction: The force that opposes motion between two surfaces that are touching each other Friction: The force that opposes motion between two surfaces that are touching each other 2 Factors influencing amount of friction 2 Factors influencing amount of friction Kinds of surfaces and the force pressing the surfaces together Kinds of surfaces and the force pressing the surfaces together

Friction Surfaces of objects are rough microscopically Surfaces of objects are rough microscopically Cause of friction: microwelds- when highest bumps from each surface stick together Cause of friction: microwelds- when highest bumps from each surface stick together Stronger forces pushing surfaces together = stronger microwelds Stronger forces pushing surfaces together = stronger microwelds Static friction: - the friction between two surfaces that are not moving past each other Static friction: - the friction between two surfaces that are not moving past each other

Friction Sliding friction- the reason you must continue to apply force after starting motion Sliding friction- the reason you must continue to apply force after starting motion Acts against your push Acts against your push Microwelds constantly break and reform Microwelds constantly break and reform Lack of friction = lack of motion for us and vehicles Lack of friction = lack of motion for us and vehicles Rolling friction- Friction between rolling object and surface- due to microwelds between wheel and surface it rolls over Rolling friction- Friction between rolling object and surface- due to microwelds between wheel and surface it rolls over Weakest form of friction Weakest form of friction

Air Resistance On earth- feather falls slower than tennis ball due to air resistance On earth- feather falls slower than tennis ball due to air resistance Air resistance- force acting opposite to motion of falling object Air resistance- force acting opposite to motion of falling object Depends on Speed, size, and shape of falling object Depends on Speed, size, and shape of falling object In vacuum (no air) - feather and tennis ball fall at the same rate- no air resistance In vacuum (no air) - feather and tennis ball fall at the same rate- no air resistance Terminal velocity- highest velocity a falling object can reach Terminal velocity- highest velocity a falling object can reach When the forces on a falling object are balanced When the forces on a falling object are balanced