MOTION AND FORCES
Motion - a change in position of an object,
caused by an object
Force – a push or a pull, caused by another
object
Force Can – Start Motion
Stop Motion
Change its direction
KINDS OF FORCE
TAKE NOTES!
There are many different kinds of force.
There are pushes
and pulls
electromagnetic forces
weak forces
strong forces
and gravitational forces,
Some forces are referred to as contact
forces and some are non-contact forces
TAKE NOTES!
FORCES RELATED TO BASIC PROCESSES
Blood flow in the body
 Plate movement (tectonics)

 Volcanic
eruptions
 Earthquakes
 Mountain building
Emergence of seedlings
 Erosion

A NET FORCE RESULTS IN A CHANGE OF
MOTION

The net force is the “left over” amount when all
the forces are added
(no net force)

If there is a net force, the object will change its
direction or velocity. This is called acceleration
Newton’s First Law of Motion – Law of Inertia
(Was really discovered by Galileo in 1600)
An object will remain at rest
or move in a straight line unless
it is acted on by a force.
Force - a push or a pull = Newton (N)
1 Newton = 1 kg x m/s2
Gives ENERGY to an object
Contact force - involves objects
touching each other
Long range forces - include gravity, magnetism, & electricity
Inertia - measures an object’s tendency to remain at rest or
keep moving - it is related to mass
TAKE NOTES!
Balanced forces - when the forces are equal
but in opposite directions, they will cancel
each other out. Does not cause motion.
Unbalanced forces - uneven forces acting
on an object that did not cancel each
other out. The object will move in the
direction of the larger one. Cause motion.
Friction - is a force that resists motion between surfaces
that are touching.
Static Friction - hinders a stationary
object from moving on a surface
when a force is applied to the object.
Sliding Friction- occurs when two
surfaces slides past each other
Rolling Friction - is the force that
enables a wheel to roll past on a
surface-same direction
Air Resistance - molecules in air colliding
with the forward-moving surface of an object,
slowing its motion.
Newton’s Second Law of Motion
An object acted on by an unbalanced force will accelerate
in the direction of the force, according to the formula.
Acceleration = Force (Newton) (10N) = 5N/kg or 5m/s2
Mass (Kilogram) (2kg)
Force of Gravity = Force= m x (9.8 m/s2)
9.8m/s2 = acceleration
Mass vs. Weight - Mass is the measure
of the amount of matter in an object it remains
the same.
Weight is a force = mass x (9.8 m/s2) gravity
(Mass is a measure of inertia.)
If a 50 kg person in the middle of an ice skating rink pushes
a 20 kg box with a force of 10 N, what will the acceleration be?
50 Kg
person
10 N
Force
20 Kg
box
Acceleration of the box:
Acceleration = force
mass
a = (10 N)
(20 Kg)
a = .5m/s2
Acceleration of the person:
Acceleration = force
mass
a = (10 N)
(50 Kg)
a = .2m/s2
TAKE NOTES!
WEIGHT IS A TYPE OF FORCE
Mass is a measure of how much matter an
object contains.
Weight is the result of the force of gravity
pulling on a mass.
The greater the force of gravity, the greater
the weight.
Newton’s Third Law of Motion
For every action,
TAKE NOTES!
there is an equal,
but opposite reaction.
Force always acts in equal and opposite pairs.
(Not the same as balanced forces - different objects.)
When you walk, you push backward
on the ground, and the ground pushes
forward on you.
If you put two bar magnets with opposite poles facing
one another, they will move toward each other.
TAKE NOTES!
Gravity is a force of attraction
between objects. The amount
of the force depends on the
mass of each object and the
distance between them.
GRAVITY IS A NON-CONTACT FORCE
The earth pulls on the moon while
the moon also pulls on the earth.
The sun pulls on the earth and
moon (and other planets) and
the earth and moon pull on the
sun
The earth pulls on other
planets and they also pull on
the earth
Gravity and the third law Gravity is pulling you to earth and Earth is
also pulled toward you. The same force that
keep planets in orbit, is the same force that
pulls objects down to Earth. You apply a
force to earth, but because earth is more
massive than you are, your force has little
or no effect. (While F is greater, so is m the mass.)
Newton’s laws apply to all objects, including distant
galaxies. Just as the Sun exerts a gravitational
force on Earth, Earth exerts an Equal and opposite
force on the Sun. This causes a variation
in the Sun’s rotation.
Combining the Laws
2. You leave the ground,
you accelerate in the direction
of this unbalanced force
2nd law accelerate in direction
of the unbalanced force.
3. When your feet hit the
ground, the ground exerts
an upward force on you.
When you stop
accelerating, all of the
forces are balanced.
1st law you remain at rest.
1. You push on the ground,
it pushes up on you.
3rd law -
equal/opposite reaction
Combining the Laws
1st Law - The canoe will stay until
a force moves it. This force comes
from the push of the puddles.
2nd Law - The canoe changes
speed or direction or both. The
people add mass and the paddlers
change the canoe’s acceleration by
adding a lot of force
3rd Law - The
paddlers push
water backward an action. This
backward force
produces an equal
and opposite forcea reaction in the
water - that move
the canoe forward.