Download 2.2 Types of Forces

2.2 Types of Forces
gravity
law of universal
gravitation
weight
friction
static friction
elastic force
tension force
compression force
normal force
sliding friction
rolling friction
fluid friction
2.2 Types of Forces
Gravity
• Many types of forces act on objects.
• Gravity is an attractive force between all
objects that have mass.
2.2 Types of Forces
Gravity (cont.)
• The ball does
not travel in a
straight line
because of the
unbalanced
force of gravity
acting on it.
2.2 Types of Forces
The Law of Universal Gravitation
• The Law of Universal Gravitation states
that all objects with mass are attracted to
each other.
• The magnitude of attraction depends on
the mass of each object and the distance
between them.
2.2 Types of Forces
The Law of Universal Gravitation (cont.)
• The gravitational force becomes stronger
as either or both objects increase in mass
or move closer together.
• The gravitational force becomes weaker as
either or both objects decrease in mass or
move farther apart.
2.2 Types of Forces
Weight and Mass
• Mass is the amount of matter in an object
and does not change with location.
• Weight is the gravitational force on a
object and changes with location.
• Weight is a force and a vector.
• Weight changes with height above Earth.
2.2 Types of Forces
Friction
• Friction is a force that opposes the
movement between two surfaces in contact.
• A book pushed across a table slows down
because of friction.
• Friction is an unbalanced force acting on the
book to slow it down.
2.2 Types of Forces
Static Friction
• Static friction is the force between two
surfaces in contact that keeps them from
sliding when a force is applied.
• A force is applied to a heavy box, but the
box doesn’t move.
• The forces are balanced, the force pushing
the box equals the force of static friction
pushing in the opposite direction.
2.2 Types of Forces
Sliding Friction
• When the force pushing on the box is
larger than the maximum static friction
force, the box begins to slide.
• The frictional force that acts on the sliding
box is called sliding friction.
2.2 Types of Forces
Sliding Friction (cont.)
• The book pushed across the table slows
down because of sliding friction.
• Without sliding friction, the book would
continue moving without a force being
applied.
2.2 Types of Forces
Sliding Friction (cont.)
• Usually friction is present and an
unbalancing force must be applied to
keep an object moving.
• When friction is greatly reduced, objects
move with nearly constant velocity without an
applied force.
– Rolling friction
– Smoother surfaces
– Lubricating surfaces
2.2 Types of Forces
Elastic Forces
• An elastic force occurs when a material is
stretched or compressed.
• A diving board exerts an upward elastic
force on the diver when it is bent
downward.
2.2 Types of Forces
Tension
• A tension force is a pulling force exerted
by an object when it is stretched, such as a
rubber band.
2.2 Types of Forces
Compression
• A compression force is a pushing force
exerted by a material when it is squeezed
or compressed.
• The size of the compression force exerted
by a material is equal to the size of the
force that compresses the material.
2.2 Types of Forces
Normal Forces
• A normal force is the force exerted by an
object that is perpendicular to the surface
of the object.
2.2 Types of Forces
Normal Forces (cont.)
• The cup is exerting a downward force on
the table, caused by gravity.
• The table is
exerting an
upward normal
force on the cup,
caused by
compression.
2.2 Types of Forces
Normal Forces (cont.)
2.2 Types of Forces
Normal Forces (cont.)
2.2 Types of Forces
Forces in the Horizontal Direction
• Friction balances forces applied in a
horizontal direction.
• Friction equals the horizontal force on an
object that is not changing motion.
2.2 Types of Forces
Forces in the Vertical Direction
• Upward normal force balances the
downward force of gravity on an object that
is not moving vertically.
2.2 Types of Forces
Forces in the Vertical Direction (cont.)
2.2 Types of Forces
A(n) ____ force is the force exerted
by an object that is perpendicular to
the surface of the object.
A compression
B elastic
C normal
D tension
2.2 Types of Forces
Which force causes a rolling ball
to slow down?
A sliding friction
B static friction
C normal force
D gravity
2.2 Types of Forces
The gravitational force between two
objects ____ as ____ increases.
A increases; distance
B decreases; mass
C increases; velocity
D decreases; distance