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)
Top Related