Download FRICTION

FRICTION
Friction = a force that opposes the motion of
objects that touch as they move past each other.
ALL moving objects are affected by friction.
Without friction…the world would be a very
different place.
4 Main Types of Friction
Static Friction
Static friction = the friction force that acts on
objects that are not moving.
Always act in the direction OPPOSITE to the
applied force.
APPLIED FORCE
STATIC
FRICTION
Sliding Friction
Sliding Friction = a force that opposes the
direction of motion of an object as it slides over
a surface.
Sliding friction is less than static friction…less
force is needed to keep an object moving that to
start it moving.
Rolling Friction
Rolling Friction = the friction force that acts on
rolling objects. (100 to 1000 times less than
sliding friction)
Ball bearings in these wheels greatly reduce
friction by replacing sliding friction with rolling
friction.
Fluid Friction
Fluid Friction = the force that opposes motion of
an object through a fluid. (water, air)
Fluid friction INCREASES as speed of object
INCREASES.
Fluid friction on an object moving through the
air is known as AIR RESISTANCE
Gravity
Gravity is a force that acts between any two
masses.
Gravity is an attractive force…it pulls objects
together.
Gravity can act over large distances.
Earth’s Gravity
Earth’s gravity acts
downward toward the
center of the Earth.
Fortunately, an upward
force usually balances the
downward force of gravity.
Falling Objects
Gravity causes objects to accelerate downward,
whereas air resistance acts in the direction
opposite to the motion and reduces
acceleration.
A flying squirrel takes
advantage of air
resistance to slow its fall
and increase the
distance covered in its
jump.
Terminal Velocity
Terminal velocity = the constant velocity of a
falling object when the force of air resistance
equals the force of gravity.
http://www.youtube.com/watch?v=p0IZsfzDS4s
Projectile motion
Projectile motion = the motion of a falling
object after it is given an initial forward velocity.
The combination of an initial forward velocity
and the downward force of gravity causes the
ball to follow a curved path.
Review
1.) You push on a box and are unable to move it.
What force opposes your push?
a. static friction
b. rolling friction
c. sliding friction
d. air resistance
Review
2.) Air resistance depends on
a. the velocity of a moving object
b. the weight of a moving object
c. the mass of a moving object
d. the inertia of a moving object
Review
3.) What force besides gravity acts on a
projectile?
a. weak nuclear
b. electrical
c. magnetic
d. air resistance