2. Friction, Gravity, and Pressure

3. Friction Friction - The force that one surface exerts on another when the two rub against each other. Acts in a direction opposite to the objects direction of motion. Opposes motion, eventually will cause object to stop. Strength depends on 2 factors; type of surface and how hard the surfaces push together.

4. Types of Friction 1)Sliding – solid surfaces slide over each other. (more force needed to overcome than rolling) 2)Rolling – object rolls over a surface. (Less force needed than sliding) 3)Fluid – occurs when an object moves through a fluid. (less force needed to overcome than sliding) Fluid keeps surfaces from making direct contact; reduces friction.

5. Gravity Isaac Newton realized that a force acts to pull objects straight down toward the center of Earth. Gravity – force that pulls objects toward each other. The acceleration due to gravity is 9.8m/s 2

6. Free Fall Free Fall – is when the only force acting on a falling object is gravity. In free fall; gravity is an unbalanced force Near surface of earth force of gravity is 9.8 m/s 2 ; every sec increases by 9.8m/s. All objects in free fall accelerate at the same pace regardless of mass.

7. Air Resistance All objects are supposed to fall at same rate, not always the case. Air resistance – objects falling though air experience type of fluid friction. Not the same for all objects Air resistance increases with velocity, eventually equals force of gravity and is balanced; no acceleration Terminal velocity- the greatest velocity an object reaches

8. Growth of Seedlings Plants grow vertically; response to gravity – Gravitropism Stem grows up (opposite of gravity), roots grow down (direction of gravity)

9. Weight Weight - measure of the force of gravity on an object. Mass – amount of matter in an object.