AIM: What factors affect friction and gravity and why acceleration during free fall? OBJ: Given notes and activity sheet SWBAT explain the factors affecting friction and gravity and why acceleration during free fall with 70% accuracy. DN: Distribute Friction and Gravity Packet ACT: Introduction to Friction (Factors Affecting Friction, Types) and Gravity (free fall, air resistance, terminal velocity, projectile motion). HW: Text, read p. 42-50, Complete Friction and Gravity Packet; SFFG Exam, April 28

Friction Notes Friction: the force that two surfaces exert on each other when they rub against each other. Factors Affecting Friction: 1) surfaces pushing together 2) rough versus smooth surfaces 3) lubricants (oils, grease) Example: Press (rub) forcefully ~ high friction Rough surface ~ high friction Press (rub) lightly ~ low friction Smooth surface ~ low friction

Sliding Friction: friction when two surfaces slide over each other. Friction: a force that acts in a direction opposite to the direction of the object’s motion. Four (4) types: Static Friction: friction that acts on objects that are not moving. Static greater than sliding, rolling, fluid friction. Sliding Friction: friction when two surfaces slide over each other. Rolling Friction: friction when an object rolls across a surface. To reduce friction, use wheels or ball bearings. Fluid Friction: Friction when an object moves through a fluid. To reduce friction, use oils & lubricants; streamline. most friction least friction static sliding rolling, fluid

Types of Friction Fluid friction

Gravity Notes Gravity: is an attractive force between objects containing mass. Factors Affecting Gravity: Mass - amount of matter (atoms) in an object Distance - length between two points increase mass ~ increase gravity increase distance ~ decrease gravity

Weight & Mass Weight = gravity x mass So: Mass: the amount of matter (atoms) in an object. Weight: the gravitational force exerted on an object’s mass. Weight = gravity x mass So: more weight(person) = more gravity(earth) x same mass(person) less weight(person) = less gravity(moon) x same mass(person) Why? Moon ~ less mass, less gravity Earth ~ more mass, more gravity (10x Moon)

Gravity & Motion Free Fall: only gravity acting on a falling object. Objects accelerate as they free fall because gravity is an unbalanced force. In a vacuum, all objects in free fall accelerate at the same rate regardless of their masses. Gravitational acceleration near Earth is 9.8 m/s2. Bowling Ball Feather drop (start at 2:35 minutes) https://www.youtube.com/watch?v=E43-CfukEgs

Air Resistance: is a type of fluid friction as an object falls through the air. Greater surface area of object ~ increase in air resistance ~ slower the object falls. Air resistance increases as velocity increases.

Gravity & Motion Terminal Velocity: maximum velocity of a free falling object occurs when the force of air resistance equals the weight of the object. Terminal velocity represents balanced forces where upward air resistance equals downward gravity.

Projectile Motion: Projectile: an object that is thrown Projectile Motion: Projectile: an object that is thrown. A projectile (with horizontal motion) will fall at the same rate as any dropped object. Trajectory: path projectile takes (curve, arc)