force

a push or a pull
has magnitude and direction
 arrows represent the magnitude
 arrowhead represents the direction


shown in Free Body Diagrams
common types of forces
Force
Symbol
Definition
Direction
Friction
Ff
The contact that
acts to oppose
sliding motion
between surfaces
Parallel to the
surface and
opposite the
direction of sliding
Normal
FN
The constant force
exerted by a
surface on an
object
Perpendicular to
and away from the
surface
Tension
FT
The pull exerted by
a string, rope, or
cable when
attached to a body
and pulled taut
Away from the
object and parallel
to the string, rope,
or cable at the point
of attachment
finding net force

Two horizontal forces, 225 N and 165 N
are exerted in the same direction on a
crate. Find the net horizontal force on
the crate.

If the same two forces are exerted in
opposite directions, what is the net force
on the crate? Be sure to indicate the
direction of the net force.
defining systems

draw a picture that defines each system:
 a piano hanging from a pulley at rest
 a book on top of a table being pushed to the
left
 a ball resting in your hand
newton’s second law of motion
Fnet
a
m

a shopping cart full of groceries has a mass
of 150 kg. if you push the cart to the right
with 1500 N, what will the acceleration of
the cart be?

a semi-truck accelerates at 6 m/s2. if the
mass of the truck is 5000 kg, what force on
the truck must the engine produce?
mass and weight

mass is the measure of matter in an
object; a fundamental property of an
object that is not affected by the forces
that act upon it

weight is a measure of the gravitational
force exerted on an object
acceleration due to gravity

the rate at which an object accelerates
towards the center of the Earth

on Earth g= 9.8 m/s2

On Earth, a scale shows that you weigh 585
N, what is your mass?

What would the scale read on the moon if
g=1.6 m/s2?
newton’s first law of motion

an object at rest will remain at rest

an object in motion will remain in motion

unless acted upon by an unbalanced
force
inertia

a property of mass

the tendency an object has to resist a
change in motion
newton’s third law of motion

all forces come in pairs

for every action there is an equal and
opposite reaction

force pairs do not cancel because they
act upon different surfaces

a physics textbook is motionless on the top of a
table. If you give it a hard push with your hand,
it slides across the table and slowly comes to a
stop. Use Newton’s 3 Laws to answer the
following questions.
1.
why does the book remain motionless before the force of the
hand is applied?
2.
why does the book begin to move when your hand pushes
hard enough on it?
3.
why does the book eventually come to a stop?