Download What is a Force? (PowerPoint)

What is a force?
Pick up 2 sheets in the back
 Watch
the book
 What
am I doing in all of these
demonstrations?
I
am applying a force
 Definition
Any
of FORCE
push or pull that causes an
object to change its current state of
motion or shape
 Can
forces be seen?
No–
only the result of the
application of the force can be seen.
 Watch
You
the ball:
can’t see the force I apply to the
ball.
You can only see the result of the
force
the
ball moves
What
is the unit of force?
A
Newton- named after Sir Isaac
Newton
Abbreviation – capital N
What
A
does it mean?
force of 1 N gives an
acceleration of 1 m/s/s to a 1kg
mass.
 Forces
can be used to change the
state of motion of an object or change
the shape of the object.
Forces can result in
start objects moving
ACCELERATIONS
 Can stop moving objects
 Can change the direction of an object’s
motion
 Can change the shape of an object
 Can
Crumpling
a piece of paper
 Sometimes
you can exert a force on
an object and no change in motion or
shape occurs.
 These types of forces are called.
 balanced
 Definition
forces
of balanced force:
 A force
that produces no change.
 A force that has an equal and opposing
force.
Equal
in size and opposite in direction

Example: A person sitting in a chair. (Force arrow
diagram)
100 N
100 N
 Arrows
symbolize forces. These arrows
have both size (scientists call it
magnitude) and direction. Therefore,
force is a vector quantity.
 The forces we spoke of earlier, the ones
that changed the state of motion of an
object or the shape of the object are called
UNBALANCED FORCES. This is the type
of force needed to produce motion.

Example : A person who breaks a chair by sitting on it.


Unbalanced forces produce a net force. A net force
causes a change in the current state of motion of an
object. It can also cause the shape of an object to
change.
Example: Tug of war (Force arrow diagram)
Net force = 5 N to the left
Before we go any further we need to talk about
types of forces. There are many types of forces
but we will only touch on seven in detail. There
are two others I’d like to mention:
 Nuclear force: The strong nuclear force is the
force that holds the protons and neutrons
together in the nucleus of atoms.
 Molecular force: The attraction of molecules
for each other results in two kinds of forces.
 Cohesion-force of attraction between like
molecules (ever do a belly flop?)
 Adhesion-force of attraction between unlike
molecules (tape, glue-adhesives)

Applied Force
Gravity Force “weight”
Normal Force
Balanced forcesno change in
current state of
motion
Frictional Force
•Friction opposes motion
•Must be contact between two
surfaces
Air Resistance
•Unbalanced forces
•object accelerates
Air Resistance #2
•Piece of paper
falling to the
ground
•Balanced forces
•Object falls at a
constant speed
Tensional Force
Teachers Win!
Spring Force
•Mass hanging on spring
•Stretched spring
•Spring wants to return to
rest position
Spring Force #2
•Compressed Spring
•Spring wants to return to rest position
Free Body Diagrams
Divide the front side into 6 equal boxes
 Divide
the back into 4 boxes
 Create
the 10 diagrams for
homework.
 Follow
the directions
 Read the descriptions carefully.