Friction

What is friction?
Friction is a force, affects motion. Friction acts on materials in contact with another, or acts in different direction in opposite motion.

What does the force of friction depend on?

 * Nature of the materials.
 * How hard the surfaces are pressed together

..such as Rubber vs. Concrete, and not Steel vs. Steel (Rubber vs. Concrete > Steel vs. Steel)

Static Friction :
Friction between the surfaces in contact and which are relatively at rest.
 * Opposes movement of stationary object
 * Moving furniture
 * Hardest part getting moving

Kinetic Friction

 * Acts on objects in motion
 * Once object begins moving, less force to keep in motion
 * Sliding, Rolling, Fluid

Sliding Friction

 * Two objects slide past one another
 * Basketball shoes prevent slipping

Rolling Friction

 * Objects such as wheel or ball rolls across surface
 * Easier to overcome than sliding friction
 * Rolling friction is always less than static friction, as the time period for contact of irregularities between the bodies is less in rolling friction compared to static friction.

Fluid Friction

 * Solid objects move through fluids
 * Cyclists use aerodynamic and spandex to reduce friction
 * Vehicles such as aeroplanes and cars have a special shape known as streamlined shape to reduce windshear or drag.

Air Resistance

 * Friction acting on something moving through air
 * Don't notice unless at high speed.

quiz
{What is ________? It is a force that affects motion and acts on materials in contact with another, or acts in a different direction in opposite motion. + friction - gravity - inertia - tension
 * type="[]"}
 * Correct! Friction is the force that affects motion and acts on materials in contact with another.
 * Incorrect. Gravity is a force that attracts two bodies toward each other.
 * Incorrect. Inertia is the resistance of any physical object to any change in its state of motion.
 * Incorrect. Tension is a force that is exerted equally in opposite directions.

{What does the force of friction depend on? It depends on the ________ of the materials and how hard the surfaces are ________ together. + nature | pressed - weight | pulled - volume | pushed - density | separated
 * type="[]"}
 * Correct! The force of friction depends on the nature of the materials and how hard they are pressed together.
 * Incorrect. Weight is not a direct factor in friction, and pulling is not the action described.
 * Incorrect. Volume is not a direct factor in friction.
 * Incorrect. Density is not a direct factor in friction, and separation decreases friction.

{Which type of friction opposes the movement of a stationary object and is evident when moving furniture? + static friction - kinetic friction - rolling friction - fluid friction
 * type="[]"}
 * Correct! Static friction opposes the movement of stationary objects.
 * Incorrect. Kinetic friction acts on objects in motion.
 * Incorrect. Rolling friction is when an object rolls across a surface.
 * Incorrect. Fluid friction is when solid objects move through fluids.

{Which type of friction is related to basketball shoes preventing slipping? + sliding friction - rolling friction - fluid friction - static friction
 * type="[]"}
 * Correct! Sliding friction occurs when two objects slide past one another.
 * Incorrect. Rolling friction is when an object rolls across a surface.
 * Incorrect. Fluid friction is when solid objects move through fluids.
 * Incorrect. Static friction opposes the movement of stationary objects.

{Which type of friction is always less than static friction due to the short time period for contact of irregularities between the bodies? + rolling friction - sliding friction - fluid friction - kinetic friction
 * type="[]"}
 * Correct! Rolling friction is always less than static friction.
 * Incorrect. Sliding friction occurs when two objects slide past one another.
 * Incorrect. Fluid friction is when solid objects move through fluids.
 * Incorrect. Kinetic friction acts on objects in motion.

{Which type of friction is related to a boy with a helmet on training wheels and cyclists using aerodynamic gear and spandex? + fluid friction - rolling friction - sliding friction - static friction
 * type="[]"}
 * Correct! Fluid friction is when solid objects move through fluids, like air.
 * Incorrect. Rolling friction is when an object rolls across a surface.
 * Incorrect. Sliding friction occurs when two objects slide past one another.
 * Incorrect. Static friction opposes the movement of stationary objects.

{What is the friction called that acts on something moving through air, especially noticeable at high speeds? + air resistance - fluid friction - sliding friction - static friction
 * type="[]"}
 * Correct! Air resistance is the friction acting on something moving through air.
 * Incorrect. While air resistance is a type of fluid friction, the specific term for friction in air is "air resistance".
 * Incorrect. Sliding friction occurs when two objects slide past one another.
 * Incorrect. Static friction opposes the movement of stationary objects.