Transcript force and motion unit

FORCE AND MOTION UNIT
WHY
DO SOME CARS GO FASTER THAN
OTHERS?
Forces
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Have you ever wondered why and how
objects begin to move and why objects
stop all of a sudden?
An object starts to move, stops
moving, or changes directions ONLY
when a force acts on it.
Some forces act on objects directly and
some forces act on objects indirectly.
For example, when you push on a door,
you directly apply the force that makes
the door open. Other forces, such as
gravity, act on objects at a distance.
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FORCE IS THE PUSH OR PULL OF AN
OBJECT. FORCES CAUSES OBJECTS TO
MOVE OR STOP MOVING.
THERE ARE MANY KINDS OF FORCES.
THE MOTION OF ANY OBJECT CAN BE
UNDERSTOOD BY LOOKING AT ALL THE
FORCES THAT ARE ACTING UPON IT.
THE STRONGER THE FORCE (push or
pull), THE MORE AN OBJECT WILL MOVE.
THE HEAVIER THE OBJECT, THE MORE
FORCE YOU MUST USE IN ORDER TO
MOVE THE OBJECT.
IF YOU PUSH AN OBJECT
A LITTLE THE OBJECT
WILL ONLY MOVE A
SHORT DISTANCE BUT IF
YOU PUSH AN OBJECT
WITH A LOT OF FORCE
THAN THE OBJECT WILL
TRAVEL FARTHER
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IF YOU PUSH AN OBJECT A LITTLE THE
OBJECT WILL ONLY MOVE A SHORT
DISTANCE BUT IF YOU PUSH AN OBJECT
WITH A LOT OF FORCE THAN THE
OBJECT WILL TRAVEL FARTHER.
FORCE AND MOTION
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LETS SAY YOU WANT
TO MOVE A CHAIR,
YOU ARE APPLYING
FORCE TO IT. YOU
PULL OR PUSH IT IN
THE DIRECTION YOU
WANT TO MOVE IT
AND WHERE YOU
WANT YOUR FINAL
POSITION TO BE.
NOTHING CAN MOVE
WITHOUT A FORCE
BEING APPLIED TO
IT!!!
MOTION can be described
Determining Motion by its position and how that
position changes over time.
If an object is moving slowly,
its position will also change
 Imagine that you are
watching an object move, if slowly.
the object suddenly
Motion can be described
changes direction, then a
using the directions north,
force has acted on it. What
south, east, and west.
if the object stops moving?
You can describe motion
 If an objects motion
as the ball moved 20 feet
changes suddenly, then
new force has acted upon
east of the goal.
it.
A compass will measure
motion.
Position
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Position is the location of an object.
For example, when a soccer ball is kicked, it moves
from its original position to another position and
you can say the soccer ball was kicked from the
sideline to the goal. The sideline and goal are the
position.
Position and direction are very helpful when
describing the motion of an object!!!
A meter stick or ruler will measure position.
Speed
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Speed is a measurement
of distance over time
such as seconds,
minutes, hours, days,
weeks, years, etc.
You can measure speed
with a clock or stopwatch
will measure time and
speed.
Scientist can calculate
speed by dividing
distance over time.
DETERMINING SPEED
SPEED = DISTANCE
Time
Speed equals the total distance divided by the
amount of time it took
QUESTION:
What is the speed of a train traveling 100
miles in 2 hours?
Answer: 50 mph
What is the speed of a car traveling
225 miles in 3 hours?
Answer: 75 mph
QUESTION
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Is it reasonable to say that because
a cheetah can run 60 miles per
hour, it will be able to run 240 miles
in 4 hours?
Why or why not?
Velocity
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Velocity measures distance over
time like speed but it also includes
direction.
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For example, the soccer ball moves
20 meters per second across the
field.
Factors that Affect Motion
Objects that are in motion or are
moving have inertia and
momentum.
INERTIA is when an object at rest or
that is not moving will stay at rest
and an object in motion will stay
in motion at the same rate,
speed, and direction unless
another force acts upon.
The force may also change the
direction of the object that was in
motion.
All objects have inertia whether they
are moving or at rest.
Hard to move objects, have a lot of
inertia an easy to move objects
have less inertia. For example, a
box of books will have more
inertia then a box of feathers.
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A SOCCER BALL AT REST
WILL REMAIN AT REST,
UNLESS A FORCE (LIKE A
KICK)IS APPLIED TO IT.
ONCE THE BALL IS
KICKED, THE BALL WILL
CONTINUE TO MOVE
UNTIL ANOTHER FORCE
STOPS IT.
Example of inertia
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HAVE YOU EVER SEEN A MAGICAN PULL
A TALBECLOTH OUT FROM UNDER
DISHES AND THE DISHES STAY PUT?
SINCE THE DISHES HAVE INERTIA, THEY
STAY PUT AND ONLY THE TABLECLOTH
MOVES BECAUSE THE FORCE (PULL) IS
ONLY APPLIED TO THE TABLECLOTH, NOT
THE DISHES!!!
A moving object also has
momentum.
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momentum: is the force of speed and
movement and it occurs when an object is
already moving. It can increased or
degrease an objects speed. It also measure
how difficult it is to slow down or stop an
object
Momentum is changed by how fast an object
is moving and how much mass (the amount
of matter in an object) that object has.
If two objects have the same velocity, the
one with the greater mass has more
momentum.
For example: a moving train has more
momentum than a moving soccer ball.
Question for Momentum
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Which would be harder to stop?
A toy truck moving in a straight line
at 50 mph or a real truck with the
same velocity?
The real truck would be harder to
stop because its greater mass gives
it more momentum then the toy
truck.
Question for Momentum
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Which would have more
momentum, a baseball thrown soft
and gently or a baseball thrown
hard and with a lot of force?
The baseball thrown with a lot of
force will have greater velocity and
have greater momentum.
Velocity can give even small objects
a lot of momentum.
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Friction can also change an
objects motion or cause an
object to stop.
As a soccer ball moves along
the ground, the ground acts
on it. The ground pushes
against the ball and slows it
down. This force is called
friction.
Friction is the force that
acts on an object to stop its
motion or slow down its
motion.
Friction acts in the opposite
direction of the direction in
which an object is moving.
FRICTION
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Acceleration
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When an object starts,
stops, speeds up,
slows down. Or turns,
it changes velocity
and any change in
velocity is called
acceleration.
Suppose you are riding
a bike, when you start
pedaling, you
accelerate, when you
turn a corner, you
accelerate because you
are changing direction.
Finally when you stop
the bike you accelerate
because the speed
changes. The only time
you are not accelerating
is when you are riding in
a straight line at the
same speed!!!
Potential and Kinetic Energy
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POTENTIAL ENERGY: IS
STORED ENERGYIN AN
OBJECT.
EXAMPLE: HOLDING A
BASKETBALL IN YOUR
HAND.
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KINETIC ENERGY: IS
ENERGY IN MOTION.
EXAMPLE: DRIBBLING A
BASKETBALL.
Forces Change Motion
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The motion of an object
depends on the force acting
on that object. Thrust, Drag,
and Lift are forces that affect
the motion of an object.
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Thrust is the force that
moves an object forward.
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A sharks tail provides forward
thrust and the faster the
shark moves its tail, the more
thrust it will have and the
faster it will move through the
water.
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Drag happens in the opposite
direction of force and slows
down an object in motion.
Drag is the force of water as it
is pushed out of the way of the
moving shark.
Lift is another force that pushes
objects up and is created by
force and pressure.
In this case, the water pushes
up the shark in the water.
The shark CAN control lift and
thrust by its motion but cannot
control drag.
drag
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thrust
Lift
FORCES:
Examples: gravity, friction,
magnetic,
Balanced forces DO NOT
change the motion of objects
Unbalanced forces DO change
the motion of objects
Balanced and Unbalanced Force
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Balanced forces have a net
force of zero. One example
of when net force is zero is
when there are equal forces
in opposite direction.
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Net force is the total force
acting upon an object. For
example, when an object is
resting on a table it is
balanced.
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When you subtract the force
pushing up on the apple from
the force pulling down on the
apple, the net force of the
apple is zero.
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Unbalanced forces
have a net force
greater than zero.
Imagine in a tug of
war contest, one
person starts to pull
harder, the net force
will no longer be
zero. There will be a
net force in the
direction of the
larger force and the
people will move in
that direction.
TENSION
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TENSION IS THE FORCE MADE BY A TIGHT OR
STRETCHED OBJECT, SUCH AS A SPRING.
THE TIGHTER THE OBJECT IS PULLED, THE GREATER THE
TENSION.
SOMETIMES THE TENSION BECOMES TOO GREAT AND
THE OBJECT BREAKS.
SPRINGS ARE ABLE TO HOLD A LOT OF TENSION,
THEREFORE, THEY ARE USED IN MANY MACHINES!!!
GRAVITY & GRAVATION
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GRAVITY IS THE
FORCE THAT HOLDS
THINGS TO THE
SURFACE OF THE
EARTH.
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GRAVATION IS THE
FORCE THAT PULLS
ALL OBJECTS IN THE
UNIVERSE TOWARD
ANOTHER OBJECT.
WHEN 2 OBJECTS AE
CLOSER TO EACH
OTHER THEY ARE
PULLED TOGETHER
WITH GREATER
GRAVATIONAL FORCE.
ENERGY and WORK
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WORK IS THE USE OF FORCE TO MOVE AN
OBJECT THROUGH A DISTANCE. IF THE
OBJECT DOES NOT MOVE THEN YOU ARE
DOING NO WORK!
ENERGY IS THE ABILITY TO DO WORK OR
TO MAKE SOMETHING HAPPEN.
THERE ARE TWO KINDS OF ENERGY:
POTENTIAL AND KINENTIC ENERGY.
Forms of Energy and Machines
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Heat energy, light
energy, sound energy,
chemical energy (burning
match), and mechanical
energy and electrical
energy are all forms of
energy.
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All machines require
work. Even machines
that are not plugged into
the wall use energy. For
example a windmill uses
the energy from moving
air to move. Other
machines use gravity.
Simple Machine
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A tool that makes work easier.
Have few or no moving parts
Use energy to do work
Simple Machines
Pulley: uses grooved wheels and a
rope to raise, lower, or move a
load. Many windows are raised and
lowered using pulleys.
Wheel: with a rod through its center
lifts or moves loads. The rod is
called an axle. Cars and trucks
have for wheels and four axles.
Lever: a stiff bar that rests on a
middle support. A lever, such as a
see-saw, can be used to lift or
move loads.
Inclined Plane: a slanted surface.
It is much easier to move an object
up an inclined plane than straight
up.
Wedge: has at least one slanted
side that ends in a sharp edge. An
axe blade is a wedge that cuts
material apart.
Screw: is an inclined plane that is
wrapped around a pole. Screws
hold things together and can be
used to lift materials.
First Class Lever
A Type 1 Lever.
First Class Levers
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A Type 1 Lever. In a Type 1 Lever, the pivot (fulcrum) is
between the effort and the load. In an off-center type
one lever (like a pliers), the load is larger than the
effort, but is moved through a smaller distance.
Examples of common tools (and other items) that use a
type 1 lever include:
Item
Number of
Class 1 Levers
Used
see-saw
a single class 1
lever
hammer's claws
a single class 1
lever
scissors
2 class 1 levers
pliers
2 class 1 levers
Second Class Lever
A Type 2 Lever.
Second Class Levers
In a type 2 Lever, the load is between the pivot
(fulcrum) and the effort.
Examples of common tools that use a type 2 lever
include:
Item
Number of Class 2 Levers
Used
stapler
a single class 2 lever
bottle
opener
a single class 2 lever
wheelbarro
w
a single class 2 lever
nail clippers
Two class 2 levers
nut cracker
Two class 2 levers
Third Class Lever
A Type 3 Lever.
Third Class Levers
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In a Type 3 Lever, the effort is between the pivot
(fulcrum) and the load. Examples of common tools that
use a type 3 lever include:
Item
Number of Class 3 Levers
Used
fishing
rod
a single class 3 lever
tweezers
Two class 3 levers
tongs
Two class 3 levers
Simple Machine