1. 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 , Complete Friction and Gravity Packet; SFFG Exam, April 27

2. 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

3. 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

4. Types of Friction
Fluid friction

5. 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

7. 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)

8. 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)

9. 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.

10. 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.

11. 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.