Download Force

Falcon Focus
• What number do you get when you multiply all
of the numbers on a telephone's number pad?
• Essential Question: A snail was traveling across
a sidewalk. A brilliant physics student decided
to find the snail’s speed and so she found a
ruler and a stopwatch. Is the student going to
find the snail’s average speed or instantaneous
speed? Explain.
Agenda
• FF
• EQ
• Recognition of Motion Graphs and
Interpretations Race
• Work on Packets
• Ticket out the door
• Closure
Tuesday
• Falcon Focus: What always goes to
bed with its shoes on?
• Essential Question: How does friction
affect an object’s motion?
SPEED
Describes how fast an object
is moving.
Average Speed =
distance
time
Velocity
The speed of an object in a
certain direction.
Velocity
d
V= t
speed of an object in a
certain direction.
V = velocity (meters/second)
d = distance (meters)
t = time (seconds)
Velocity
speed of an object
in a certain
direction.
0
3 seconds 1
2
Scalar
a measurement that does
NOT contain direction.
Egg sample: Speed
Vector
a measurement that contains
direction.
Egg sample: Velocity
2 Volunteers
• Socks vs. Shoe Friction Demontration
Questions
• does it make a difference sliding in socks?
explain.
•
• Is it easier or harder on carpet than wood
or tiles?
•
• how do you think friction affects motion
based on what you observed?
• Standard 8-5.3. Analyze the effects of
forces (including gravity and friction) on
the speed and direction of an object.
•
What is a force?
• A force is a push or pull
Types of Forces
• 1. Gravity
• 2. Friction
• Forces such as gravity and friction can
affect the speed and direction of an
object.
•
Friction
• Friction is a force that occurs when one
object rubs against another object.
• Friction is the Force that one surface exerts
on another surface when they are moving
across each other.
• Friction will cause a moving object to
slow down and finally stop.
• Two factors determine the amount of
friction –
• (1) the kinds of surfaces, and
• (2) the force pressing the surfaces
together. (how hard the surfaces are pushed
together during the motion )
– The slowing force of friction always acts in
the direction opposite to the force causing the
motion.
– Friction Opposes motion
• Examples: rubbing hands together, gym
sneakers allowing you to stop better on the
gym floor (compared to dress shoes)
• Friction can also be the force that makes
it difficult to start an object moving.
• Enough force must be applied to a
nonmoving object to overcome the
friction between the touching surfaces.
• The smoother the two surfaces are, the less
friction there is between them; therefore,
the moving object will not slow down as
quickly.
– Friction between surfaces can be reduced, in
order for objects to move more easily, by
smoothing the surfaces, using wheels or
rollers between the surfaces, or
lubricating/oiling the surfaces.
– If friction could be removed, an object would
continue to move.
• The greater the force pushing the two
surfaces together, the stronger friction
prevents the surfaces from moving.
– As an object gets heavier, the force of friction
between the surfaces becomes greater.
– To move a heavy object, a greater force must
be applied to overcome the friction between
the surfaces.
Less or More Friction
Less or More
Less or More
Less or More
Friction Lab
• Title: Car Friction Lab
• Problem: How does the texture of the tracks
affect the speed of the cars?
• Explanation: Today you experiment on different
types of textures to see how friction affects its
motion.
Closure
• Friction Lab Conclusion/TOD
• HOW DID FRICTION AFFECT THE
CARS' RACING TIMES?
•
• why is friction considered a force?
Wednesday
• Falcon Focus: WHAT TWO THINGS CAN
YOU NEVER EAT FOR BREAKFAST?
• ESSENTIAL QUESTION: HOW DOES
MASS AND DISTANCE AFFECT GRAVITY?
Family Guy Video
• What is gravity?
•
• Why is gravity considered a
force?
Gravity (force that pulls objects down)
• Gravity is a force that always attracts or pulls
objects toward each other without direct contact
or impact.
• Gravity is a force of attraction, or a pull,
between objects.
• Gravity pulls objects down.
• Do gravity affects everything? ____________
• Gravitational attraction depends on the
mass of the two objects and the distance
they are apart.
• Objects on Earth are pulled toward the
center of Earth.
• The force of gravity, like all other forces,
can cause changes in the speed of objects.
• As an object falls, its speed will
continually increase as Earth’s gravity
continually pulls it downward.
• Gravity can also cause an object that is
thrown into the air to change its upward
motion, slow down, and fall back toward
Earth’s surface.
• The pull of Earth’s gravity keeps the
Moon in orbit; the moon is constantly
changing direction because of gravity.
How Does Mass Affect Gravity?
• Imagine an elephant and a cat. Because the elephant
has a larger mass than the cat does, gravity between the
elephant and Earth is larger. So, the cat is much easier
to pick up than the elephant. The gravitational force
between objects depends on the masses of the objects.
• Objects with Larger or Heavier Mass has a larger
gravitational attraction?
• Objects with a smaller mass has a smaller
gravitational attraction.
How Does Distance Affect Gravity?
• The mass of the sun is 300,000 times bigger than that of Earth.
However, if you jump up, you return to Earth every time you
jump rather than flying toward the sun. If the sun has more mass,
then why doesn’t it have a larger gravitational pull on you?
• This is because the gravitational force also depends on the
distance between the objects.
• As the distance between two objects gets larger or further, the
force of gravity gets much smaller.
• And as the distance between objects gets smaller or shorter, the
force of gravity gets much greater.
• Although the sun has tremendous mass, it is also very far away. This means
that it has very little gravitational force on your body or on small objects
around you. The sun does have a large gravitational force on planets because
the masses of planets are very large.
Air Resistance
• When air resistance is ignored, all objects
will speed up at the same rate as they fall.
• What is air resistance? Air resistance
opposes the downward motion of a falling
object.
• Any falling object meets air resistance.
Questions
• WHAT TWO THINGS DETERMINE
GRAVITATIONAL FORCE?
•
• do all objects have a gravitational
force? explain your answer.
•
Center of Gravity Lab
• “BET YOU CAN’T BALANCE” CHALLENGES*
• Use what you've learned about balance to compete
with your friends and family with following balance
challenges.
• HERE WE GO!!!!!!
• http://nanaimoscience.org/wpcontent/uploads/2014/04/PlaygroundPhysics1.pdf
Questions
• IS THERE MORE GRAVITATIONAL FORCE
BETWEEN OBJECTS WITH SMALL MASSES OR
OBJECTS WITH LARGE MASSES?
•
• THE SUN IS MUCH MORE MASSIVE THAN
EARTH. WHY IS THE FORCE OF GRAVITY
BETWEEN YOU AND THE SUN SO MUCH LESS
THAN EARTH’S GRAVITY AND YOU?
•
• HOW DOES AIR RESISTANCE AFFECT AN
OBJECT’S MOTION?
•
HW
• STUDY FOR QUIZ
THURSDAY
• FALCON FOCUS:
There was a window cleaner who was
cleaning a window on the 25th floor of a skyscraper. He
suddenly slips and falls. He has no safety equipment and
nothing to soften his fall, but he is not hurt at all. How do you
account for that?
• ESSENTIAL QUESTION: HOW DOES MASS
AND DISTANCE AFFECT GRAVITY?
QUIZ TIME
INTRO TO CAR PROJECT
CLOSURE
FRIDAY
• FALCON FOCUS: WHAT IS IN THE
MIDDLE OF THE SKY?
• ESSENTIAL QUESTION: HOW WOULD
YOU EXPLAIN THE DIFFERENCE BETWEEN
BALANCE AND UNBALANCE FORCES?
DEMONTRATION TIME !!
• ARM WRESTLING
QUESTIONS
• Explain balanced forces. How do they
affect the motion of an object?
•
• Explain unbalanced forces. How do they
affect the motion of an object?
Force and Mass
• 8-5.4
Predict how varying the amount
of force or mass will affect the motion of
an object.
•
•
• Varying the amount of force or mass will
affect the motion of an object.
Force: A Push or Pull
• If an object is in motion and more force is
applied to it, the object will begin moving
faster.
• If two objects have the same mass and a
greater force is applied to one of the
objects, the object which receives the
greater force will change speeds more
quickly. For example if a ball is hit
harder, it will speed up faster.
Forces
• If an object must be slowed down quickly,
the force applied to the object must be
greater than what is needed for a gradual
slowing down. For example, the greater
the force applied to the brakes of a
bicycle, the more quickly it will slow
down or stop.
Forces
• Varying the amount of force applied to a
moving object can also change the
direction that the object is moving more
or less quickly. For example, a baseball
pitched toward the batter may quickly
change direction and speed if hit very
hard, or may change direction and speed
more slowly if hit softly as with a bunt.
Mass
• What is Mass?
• Mass is the amount of matter in an object.
• What is matter?
• Matter is anything that has mass and
volume.
Mass
• If a heavy (more massive) object is in
motion, more force must be applied to get
the object moving faster.
• If the same force is applied to two objects,
the object with the smaller mass will
change speeds more quickly. For
example if a baseball and a bowling ball are
thrown with the same force the baseball will
speed up faster.
Mass
• In order to slow down or stop a heavier
(more massive) object, the force on that
object must be greater than for a less
massive object. For example, if the same
braking force is applied to a small car and a
large truck, the car will slow down more
quickly.
Mass
• It is more difficult to change the direction
of a heavy moving object, than one that is
lighter in mass.
What is the difference between
weight and mass?
WEIGHT
• Weight is a measure of the force gravity on
an object
MASS
• Amount of
matter in an
• Weight is a force
object
• (Weight varies according to the
• Mass is not a
force of gravity pulling on you)
force
Therefore, Your weight will
• Mass is the same
vary depending on your
anywhere on
location (On top of a mountain
Earth
vs. being at sea level.
• Mass is constant
• Weight can change
Closure
• What 2 things can affect the motion of an
object?
• What is the difference between weight and
mass?
• What is force?
• What is the relationship between force and
mass?
Flash Back Quiz
1. Name the 3 types of rocks and the location where they
form.
2. What process a rock would have to go through in order to
become an igneous rock?
3. What process a rock would have to go through in order to
become a metamorphic rock?
4. What process a rock would have to go through in order to
become a sedimentary rock?
5. Name and explain the 2 types of igneous rocks.
• 8-5.5
Analyze the resulting effect of
balanced and unbalanced forces on an
object’s motion in terms of magnitude
and direction.
Forces
• Forces have a magnitude (strength) and a
direction. (The unit for Force is Newton
(N)
Forces
• Forces can be represented as arrows with
the length of the arrow representing the
magnitude or strength of the force and
the head of the arrow pointing in the
direction of the force.
• Using such arrows, the resulting force (net
force) and direction can be determined.
Balance vs. Unbalance Forces
• Forces acting on an object can be
balanced or unbalanced.
Balance Forces
• Balanced forces will cause no change in
the motion of an object. (No Movement)
• Balanced forces acting on an object in
opposite directions and equal in strength,
as shown in the arrows below, do not cause
a change in the speed/magnitude or
direction of a moving object.
Balance Forces
• Objects that are not moving will not start
moving if acted on by balanced forces.
– For example, in arm wrestling where there is no
winner, the force exerted by each person is
equal, but they are pushing in opposite
directions. The resulting force (net force) is
zero.
•
• 5N
5N
Balance Forces
– Or, in a tug of war, if there is no movement in
the rope, the two teams are exerting equal,
but opposite forces that are balanced. Again,
the resulting force (net force) is zero.
•
• 5N
5N
Unbalanced Forces
• Unbalanced forces are not equal, and they
always cause the motion of an object to
change the speed and/or direction that it is
moving.
Unbalance Forces
• When two unbalanced forces are exerted
in opposite directions, their combined
force is equal to the difference between
the two forces.
– The magnitude and direction of the net force
affects the resulting motion.
– This combined force is exerted in the
direction of the larger force.
Unbalance Forces
– For example, if two students push on opposite sides of
a box sitting on the floor, the student on the left pushes
with less force (small arrow) on the box than the
student on the right side of the box (long arrow).
The resulting action (net force: smaller arrow to the
right of the =) shows that the box will change its
motion in the direction of the greater force as shown
below:
•
•
5N
10N
5N
Unbalance Forces
• Or, if in a tug of war, one team pulls
harder than the other, the resulting
action (net force) will be that the rope will
change its motion in the direction of the
force with the greater
strength/magnitude as shown below:
•
• 5N
10N
5N
Unbalance Forces
• If unbalanced forces are exerted in the
same direction, the resulting force (net
force) will be the sum of the forces in the
direction the forces are applied.
Unbalance Forces
• For example, if two people pull on an object at the same
time in the same direction, the applied force on the object
will be the result of their combined forces (net force or
longer arrow to the right of the =) as shown below:
• 5N + 10N
=
15N
Unbalance Forces
• When forces act in the same direction,
their forces are added. When forces act
in opposite directions, their forces are
subtracted from each other.
• Unbalanced forces also cause a
nonmoving object to change its motion
Balance vs. Unbalance Forces
• If there is no net force (balance force)
acting on the object, the motion does not
change . If there is net force (Unbalance
force) acting on an object, the speed of the
object will change in the direction of the
net force.
•
When the net force is Zero.
-> NO movement
When the net force is NOT Zero.
-> movement
Static Equilibrium Balanced forces
When all forces are balanced.
The net force is Zero.
There is NO movement.
3 Kg
?
2 Kg
Inertia
• 8-5.6
Summarize and illustrate the
concept of inertia.
Inertia
• Inertia is the tendency of objects to resist
any change in motion. Inertia is a
property of the object; it is not a force.
Inertia
• It is the tendency for objects to stay in
motion if they are moving or to stay at
rest if they are not moving unless acted
on by an outside force.
Inertia
• The more mass an object has, the harder it
is to start it in motion, to slow it down or
speed it up, or to turn it.
• In other words, the more mass an object
has, the more inertia it has.
The greater the mass
the harder it is to move.
And . . .
the harder it is to stop moving.
Lower mass objects are easier to move . .
.and to stop moving.
NEWTON’s Laws
1st Law of Motion :
An object remains at a
constant speed
in a straight path ,until a
net force acts on it.
NEWTON’s 1st Law of Motion
is the law of
ih ner shah
An object will
remain at a
constant speed
(unless disturbed).
Examples of the effects of inertia
might include:
• Inertia causes a passenger in a car to
continue to move forward even though
the car stops. This is the reason that seat
belts are so important for the safety of
passengers in vehicles.
•
• Inertia is the reason that it is impossible
for vehicles to stop instantaneously.
Examples of the effects of inertia
might include:
• Inertia is the reason that it is harder to start pushing a
wheelbarrow full of bricks than to start pushing an
empty wheelbarrow. The filled wheelbarrow has more
mass and therefore, more inertia.
•
• Inertia is also the reason that it is harder to stop a
loaded truck going 55 miles per hour than to stop a car
going 55 miles per hour. The truck has more mass
resisting the change of its motion and therefore, more
inertia.
•
Flash Back Quiz
Closure
Homework
UN balanced
Speed (m/s)
Gravity
BALL
Ground
Time (mSec)
Inertia
Speed (m/s)
UN balanced
PUTTER
BALL
Time (mSec)
Friction
Speed (m/s)
UN balanced
SKATE
Time (Sec)
Friction
the resistive force that occurs
when two surfaces travel past
each other.
causes physical deformation
generates heat
Friction
the resistive
force that
occurs when
two surfaces
contact each
other.
Oliver the dog doesn't want to
walk in the rain. He can make his
owner pull harder on the leash to
get him out the door by
sitting on the vinyl floor.
sitting on the tile floor.
sitting on the carpeted floor.
sitting on the wood floor.
Pauline needs to measure the sliding friction of a
brick. How should she go about doing this?
attach the brick to a string and then to a spring
scale and read the force needed to quickly lift the
brick off the ground
drag the brick by a string attached to a spring scale
so that it gradually speeds up
drag the brick by a string attached to a spring scale
along the surface of a table at a constant speed and
read the force
hang the brick from a string attached to a spring
scale and read the force
terminal velocity gravity will
accelerate an object until air
resistance (friction) does not
allow it to go any faster.
In the absence of air resistance,
which of these objects will fall at
the fastest rate when dropped?
the ball with a mass of 75 kg
the ball with a mass of 25 kg
the ball with a mass of 10 kg
They all fall at the same rate.
Gravitational force
Gravitational force
o INCREASES with Mass
o DECREASES with Distance
All objects in the universe are
attracted to each other by the
force of
effort.
friction.
gravity.
inertia.
Four pairs of objects have the masses
shown below. If the objects in each pair
are the same distance apart, the
gravitational force between the objects
in which pair is greatest?
1 kilogram and 1 kilogram
1 kilogram and 2 kilograms
2 kilograms and 1 kilogram
2 kilograms and 2 kilograms
As an astronaut travels from Earth to a
space station orbiting Earth, what
happens to her mass and weight?
Her mass decreases, but her weight
remains the same.
Her mass increases as her weight
decreases.
Her mass remains the same, but her
weight decreases.
Her mass decreases and her weight
also decreases.
Which hill would you slide down
the fastest?
hill A
hill B
hill C
It would take the same time to
slide down all of the hills.
Projectile
Motion
Velocity (m/s)
forward
downward
50 39.2
19.6
29.4
9.8
0
0
3 seconds 1
2
Projectile
Motion
Velocity (m/s)
forward
downward
46
47
48
49
50 39.2
19.6
29.4
9.8
0
0
3 seconds 1
2