Transcript Forces and Motion

Forces and
Motion
Why do objects move?
A force acts on them
A FORCE is a push or a
pull, in any direction,that
may cause a change in
an object’s motion
Will a force always cause an object
to move?
NO
Every object has several forces
always acting on them.
Gravity
Air Pressure
Friction
Air Pressure
Friction
Normal
The sum of all the forces acting on
an object is called NET FORCE
If an object is motionless, the
Net Force = 0 , The forces
are said to be Balanced.
With Balanced Forces, the
forces are equal but in
opposite directions
Since the applied force is not
The forces are said to be
stronger than the force of friction
Balanced…
the object does not move
Gravity
Air Pressure
Applied Force
Air Pressure
Friction
Normal
If a force is exerted on an object
causing it to move, this is
called an UNBALANCED
FORCE, the net force is
greater than zero and the
object moves.
If the applied
force is
strong
enough than
to over
The applied
force
is stronger
come the
existing
forces,
objectofwill
friction…
this
is an the
example
an
move
Unbalanced
force
Gravity
Air Pressure
Air Pressure
Friction
Applied Force
Normal
Some Common Forces
Friction
The force exerted when two
objects rub up against each
other.
Friction opposes motion, it
causes objects to slow down
What affects the Friction between
objects?
• Mass of the Object
• Type of Surface
• Amount of surface area
touching
Sliding Friction
Motion
Friction
Rolling Friction
The amount of friction between the two
objects is less than sliding friction
The object is easier to
move
Liquid Friction
A lubricant, such as oil, makes a thin
layer between the two objects.
Which one will move farther if an
equal force is applied
200 kg
1000 kg
Which one will move farther if an
equal force is applied
On ICE
200 kg
On Carpet
200 kg
Which one will move farther if an
equal force is applied
200 kg
200 kg
Gravity
• The force that pulls objects towards
each other
• Every object has gravity, meaning
that all objects are being pulled
toward each other.
• So why are we not being pulled
together right now?
The larger the object is, the more
we are effected by its gravitational
pull.
We are more attracted to the Earth’s
gravity than we are to gravity of the
things in the room
Where will the red ball move
Since the green ball is
bigger, its gravity effects
the red ball more than
the white ball does, so
the red ball moves
towards the green ball
Why do the two objects not hit the
ground at the same time?
Gravity is acting more
on the elephant than
on the feather. And a
heavier object
overcomes the
upward force of wind
resistance (friction)
more easily thus
falling faster than the
light object
What happens if we
can eliminate the wind
resistance?
The two objects hit the ground at
the same time
Gravity is still
acting more on
the elephant
than the feather,
but the inertia of
the elephant
keeps it from
accelerating
faster
All objects will
accelerate the
same when
the force of
gravity is the
only force
action on it.
Sir Isaac Newton and the 3 Laws of
Motion
Inertia
The resistance of an object to
changes in motion
Basically Stated… its harder to alter the
motion of a heavier object than a lighter
object
Newton’s First Law
An object in motion will stay in motion
and an object at rest will stay at rest
until acted on by a force.
Basically stated… objects keep moving until
something slows them down (friction) and
objects will stay still until something causes them
to move (force)
Newton’s First Law Applied:
As the wall stops the car… the guy
keeps going, there is nothing to
stop his forward motion
Newton’s First Law Applied:
as the truck stops, there is nothing
keeping the ladder from stopping; it
continues to move forward until
gravity and wind resistance stops it
Newton’s Second Law
Shows the relationship between an
objects mass its acceleration and
the applied force.
Basically stated… it takes a stronger force to
move a heavier object that a lighter object
and a stronger force to get an object to
move faster
Newton’s Second Law Applied:
If an equal force is applied, the less
massive object moves farther
200 kg
1000 kg
Newton’s 2nd Law Applied:
In order to move the more massive
object the same distance at, it will
take a much larger force
200 kg
1000 kg
Newton’s Third Law
For every action, there is an
opposite and equal reaction
Basically stated… apply a force in one
direction, there is the same force being
applied right back at you
Action: Thrust
Reaction: Jet
moves forward
As the swimmer pushes against
the water, the water pushes
back and the swimmer moves
forward
Which Law Applies
If you step off
a boat, the
boat is
moved
backward
THIRD
LAW
Which Law Applies
Second Law;
its harder to
throw a
heavy
object than
a light one
Which Law Applies?
Third Law: the
downward
force causes
the space ship
to go up
Which Law Applies?
nd
2
law: it takes a big force
to mover the heavy object
First Law: The object will not move
until something causes it to move
Would this cart be able
to make the loop on
this roller coaster?
Newton’s 3rd law says
every action has an
equal reaction…
Here is the
action
force…
Remember.. Equal… not
greater…
So the reaction force can
only be this high…
Here is the
action
force…
The cart would only go
this high then fall back