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 27

Friction NotesFriction: 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

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 NotesGravity: 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 & MassMass: 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 & MotionFree 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 & MotionTerminal 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. A projectile (with horizontal motion) will fall at the same rate as any dropped object.