Transcript 7 Forces and Friction Notes

Physical Science
FORCES AND FRICTION
WHAT IS A FORCE?
A push or pull on an object
 Units: Newton (N) = 1 kg x m/s2
 Net Force (Fnet) : sum of all of the forces that
are acting on an object
 Balanced Forces: Fnet = 0

 Object

is at rest or moving with constant velocity
Unbalanced Forces: Fnet is not equal to 0,
 Object
is accelerating
TYPES OF FORCES
Applied – contact force in the direction the
object is moving
 Tension - caused by a rope, cable, ect., directed
away from the object
 Friction- opposes the motion of objects, must
have contact
 Normal- caused by a surface, upward direction
 Force of gravity- force at a distance, caused by
attraction between two objects

FORCE OF GRAVITY
 Symbol:
Fg
 Units: Newtons
 Also known as weight (W)
 Definition: gravitational force exerted on
an object
 Equation: Fg (W)= mg
 g = acceleration due to gravity,
10
2
m/s
TWO TYPES OF FRICTION
1. Static
 Friction of an object at rest
 Greater than kinetic friction (harder to get
an object moving than to keep it moving)
 Friction is greatest when surfaces are rough
How can you get a car to move that is stuck
in the snow?
2. Kinetic
 Friction of a moving object
TYPES OF KINETIC FRICTION
a. Sliding
 Two
surfaces moving past each other
b. Rolling
 Movement
of a circular object on a surface
c. Fluid Friction
 Movement
of an object through a liquid or gas
 Ex. Air resistance
DRAWING FREE BODY DIAGRAMS (FBD)
1. Used to represent forces affecting an object
2. Steps:
a. Use a dot or box to represent the object
b. Identify forces affecting the object
c. Use arrows to represent the size and direction of
force (bigger arrow = greater force)
d. Connect arrows to the dot/box and label arrows
DOG WALKING AT CONSTANT SPEED
BABY BEAR RESTING
GYMNASTICS RINGS
BASE JUMPER
BOAT ACCELERATING TO THE RIGHT
DOGS ACCELERATING SLED