Friction, Gravity, and Pressure

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.

Types of Friction1) 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.

Gravity Force acts to pull objects straight

down toward the center of Earth Gravity – force that pulls objects

toward each other.

Free Fall Free Fall – when the only force acting on a

falling object is gravity. In free fall; unbalanced force Near surface of earth force of gravity is

9.8 m/s2; every sec increases by 9.8. All objects in free fall accelerate at the

same pace regardless of mass Projectile – object is thrown

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

Growth of Seedlings Plants grow vertically; response to

gravity – Gravitropism Stem grows up (opposite of gravity),

roots grow down (direction of gravity)

Weight Weight - measure of the force of

gravity on an object. Mass – amount of matter in an

object. Weight measured in Newtons

Newton’s Third Law For every action there is an equal

and opposite reaction States that if one object exerts a

force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object.

Pressure Equal to the force exerted on a

surface divided by the total area over which the force is exerted.

Force and pressure closely related by not the same.

Calculate Pressure Pressure=force/area

Measured as pascal

Pressure in a Volcano Volcano is in equilibrium as long as

the force exerted by the built-up fluid is not greater than the rock’s strength.

Fluid in volcano exerts a pressure (force); causes it to explode.

Force Pumps and Blood Flow

Heart is a force pump Blood fluid in heart, pumped through

circulatory system by heart When force is applied to a confined fluid,

an increase in pressure is transmitted equally to all parts of the fluid – Pascal’s Principle (explains how heart pumps blood through body)