Download unbalanced versus balanced

FORCE is any push or pull which
causes something to move or change
its speed or direction
What is Force?
• Force is the capacity to do work or cause
physical change
• Forces have both size and direction
• Force = mass x acceleration
• Force is measured in Newtons (N)
– N = (kg . m/s2).
• Forces are measured using a spring scale.
Types of Forces
1. Contact Forces: a push or a pull on one
object by another object that is touching it.
Ex. friction, air resistance, tension, normal,
applied, spring
2. At a Distance/Noncontact Force: a force
that one object can apply to another object
without touching it.
Ex. Gravity, Electric, Magnetic
What is friction?
• A force that resists the motion of two
surfaces that are touching. It causes heat,
damage, wear, and slowing.
What is friction?
• Types of friction:
– Static Friction: static means
having no motion.
– Sliding Friction: occurs
when a force is great enough
to overcome the static
friction.
What is rolling friction?
• Rolling friction is the
friction which enables
wheels to turn,
helping objects to
move.
• If there were no
rolling friction, turning
wheels would not
enable an object to
move.
What is fluid friction?
• Fluid friction is friction
between a surface and a
fluid.
• A fluid is any material that
flows therefore, water and
air are both fluids.
• Fluid friction between air
and a surface is air
resistance.
What causes friction?
• There are two factors which affect friction
between two surfaces:
– Kind of surfaces in contact (rough or smooth)
– Amount of force pressing the surfaces
together.
The rougher the surface and the stronger the
force between the surfaces, the greater the
amount of friction.
Reducing Friction
• Lubricant: oils, grease,
and soap
• Streamlining
(aerodynamics)
• Making surfaces rougher
·Smoothing surfaces
Friction … Pros and Cons
PROS
• Enables us to stand
and move without
falling
• Makes a pencil work
• Need friction for tires
to move a car
CONS
• Causes engine parts
to wear out
• Causes holes in your
socks
• Causes wind and
water erosion
What is tensional force?
• A force that is transmitted through a string,
rope, cable or wire when it is pulled tight
by forces acting from opposite ends.
What is normal force?
Normal force is the support
force exerted upon an
object which is in contact
with another stable
object.
Example: If a book is resting
on a table, the table is
exerting a normal force
on the book in order to
support the weight of the
book.
What is applied force?
An applied force is a force which is applied
to an object by a person or another object.
What is spring force?
Spring force is the force exerted by a
compressed or stretched spring upon any
object which is attached to it.
What is Gravitational force?
• Gravity is a force of attraction between two objects.
• Gravity is an “at a distance” force
• Law of Gravitation – any
two objects exert an
attractive force on each
other. The amount of
attraction depends upon
two things: the mass of the
objects and the distance
between the objects.
What is electrical force?
Electrical force is created by attraction of
positive and negatively charged particles
What is magnetic force?
Magnetic force is the attraction or repulsion
between electrically charged particles
because of their motion.
Forces can be BALANCED or
UNBALANCED
Balanced forces are equal in size and
opposite in direction
Unbalanced forces are not equal in size
and/or opposite in direction. If the forces
on an object are UNBALANCED, we say a
NET force results. This will result in a
change in motion!!
Net Force
Net Force =
Combination of all forces acting on an
object.
Fnet
Ffriction
Fpull
N
N
W
Balanced Forces
Net force = 0
No change in
motion
No change in
direction.
Object either at rest
or moving at a
constant velocity.
Unbalanced Forces
Net force is ≠ 0
Change in motion
Change in
direction.
Object’s motion
or direction of
motion changing.
Determine the NET FORCE:
FN
Fg
unbalanced versus balanced
test yourself
Net Force Problems
Need to know amount
of forces and their
direction.
Use free-body diagrams
to calculate net force.
Net force = the sum of
all the forces acting
on an object.
Practice Problems
Problem 1
Problem 2
A book is at rest on a
table top.
An egg is falling from a
nest in a tree.