Download Types of Friction - AustinMeehanAcademy3

Do Now
What is motion?
Objective
Students will be able to analyze and integrate
information in order to demonstrate
knowledge of how to measure motion.
Agenda
Do Now
Motion, Speed, Velocity, Acceleration
Expectations
Lab
Motion and Speed
Motion – an object’s change in position relative
to a reference point
Speed – the distance traveled divided by the
time interval during which the motion occurred
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑 =
𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒
Imagine that two birds leave the same tree at
the same time. They both fly at 10 km/h for 5
min, 12 km/h for 8 min, and 5 km/h for 10 min.
Why don’t they end up at the same place?
Velocity and Acceleration
Velocity – the speed of an object in a particular
direction
Acceleration – the rate at which velocity
changes over time; an object accelerates if its
speed, direction, or both change
𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑎𝑐𝑐𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 =
𝑓𝑖𝑛𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 −𝑠𝑡𝑎𝑟𝑡𝑖𝑛𝑔 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝑡𝑖𝑚𝑒 𝑖𝑡 𝑡𝑎𝑘𝑒𝑠 𝑡𝑜 𝑐ℎ𝑎𝑛𝑔𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
Expectations
Lab will be collected at the end of class
Work in groups of 4
If you are not completing the lab
appropriately, you will receive a 0 as a lab
grade
Raise your hand if you do not what to do
Variables
Independent: the variable that does not change
Dependent: the variable that changes
Control: the standard variable (beginning)
Procedure
Mark the floor with tape from 0 cm, 50 cm, 100
cm, and 150 cm
Set up your ramp using text books
Follow Step 3 from Procedure and follow the
directions
Do Now
What is friction?
Objective
Students will be able to analyze and integrate
information in order to explain why friction
occurs.
Agenda
Do Now
Friction
Lab/Directed Reading
While playing ball, your friend throws the ball out of
your reach. Rather than running for the ball, you walk
after it. You know that the ball will stop. But do you
know why?
Friction: a force that opposes motion between two
surfaces that are in contact.
The source of friction
Friction occurs because the surface of any object is
rough.
◦The hills and valleys of one surface stick to the hills
and valleys of the other surface.
Two factors that effect the amount of friction between
two surfaces:
◦The force pushing the surfaces together
◦The roughness of the surfaces
The Effect of Force on Friction
If the force pushing or pulling the surfaces of two objects
increases, the hills and valleys can come into closer contact
creating more friction.
◦Ex. Slide hand across desk. Then push down and slide
hand across desk.
Objects that weigh less exert less downward force than
objects that weigh more do. But changing how much of the
surfaces come in contact does not change the amount of
friction.
The Effect of Rougher Surfaces on
Friction
Rough surfaces have more microscopic hills and valleys
than smooth surfaces do. So the rougher the surface
is, the greater the friction is.
◦Ex. A ball rolling across grass compared to a puck on
the ice.
Types of Friction
There are two types of friction:
◦Kinetic Friction: Friction between moving surfaces.
◦Kinetic means “moving”
◦Static Friction: When a force is applied to an object
but does not cause the object to move.
◦Static means “not moving”
Types of Friction
Two types of kinetic friction:
◦Rolling
◦Takes less force to roll an object than to slide it.
◦Ex. Anything that has wheels uses rolling kinetic friction
◦Sliding
◦Takes more force to slide an object than to roll it
◦Ex. Applying brakes to a bicycle, writing with a pencil,
scratching an itch
Friction: Harmful and Helpful
Think about how friction affects a car. Without
friction, the tires could not push against the ground
and move the car forward, and the brakes could not
stop the car. Without friction, a car is useless.
Friction: Harmful and Helpful
Friction:
◦Can cause holes in your socks and in the knees of your
jeans
◦Can cause erosion of topsoil that nourishes plants through
wind and water
◦Allows you to write
◦Allows you to walk without slipping and falling
Sometimes it is necessary to decrease or increase friction.
Some Ways to Reduce Friction
Lubricants: substances that are applied to surfaces to reduce
the friction between the surfaces.
◦Ex. Motor oil, wax and grease.
◦Lubricants are usually liquids but they can be solids or gasses.
Friction can be reduced by switching from sliding kinetic
friction to rolling kinetic friction.
Friction can also be reduced by making a surface smoother. Ex.
Sanding a wooden bench.
Some Ways to Increase Friction
Make surfaces rougher.
◦Sand scattered on icy roads
◦Textured batting gloves.
Increase the force pushing the surfaces together.
◦Sanding a piece of wood works faster if more force is
applied.
◦Cleaning a dirty dish using a sponge
Do Now
Why is friction helpful?
Objective
Students will be able to analyze and integrate
information in order to explain why friction
occurs.
Agenda
Do Now
Review Friction
Lab/Directed Reading/Section Review
Group Work
Directed Reading
Complete the directed
reading activity with your
group.
Will be collected at the end
of the lab
Section Review
Page 19
Lab
Follow the directions from
the procedure
Use three books (2 for the
base, 1 for the incline
plane)
Use the toy car to
measure the distance
In your own words, write a definition for
the term net force.
A combination of all forces that act
on an object.
In your own words, write a definition for
the term friction.
Friction is a force between any two
surfaces, that opposes motion.
This type of force causes a change in
the speed or direction of an object.
Unbalanced force
Which direction is the force of friction
pushing against the block?
Why is it easier to slip when there is
water on the floor?
a)
The water is a lubricant that when spilled,
fills in the hills and valleys on the floor and
reduces friction between your feet and the
floor
Forces are measured in these units.
Newtons
Explain why friction occurs.
Friction occurs because surfaces
are covered with microscopic “hills
and valleys” that stick to each other
when they come in contact.
Friction is caused when microscopic hills
and valleys of objects rub together:
How does the roughness of surfaces that are
touching affect the friction between surfaces?
Rough Surfaces have more hills and
valleys that increase the force of
friction. Smooth surfaces have less hills
and valleys, therefore less friction
occurs.
Which will have more friction?
These surfaces will have
more friction because
they have larger hills and
valleys than the other
picture. This means they
are more rough.
Describe how the amount of force pushing two surfaces
together affects friction.
If the force pushing the two
surfaces together is great, the hills
and valleys are in closer contact
and friction increases.
More Force = More Friction
Name two ways in which friction can be
increased.
Make a surface rougher
Push surfaces together harder
List the two types of friction, and give an
example of each.
Kinetic- sliding a book across the
tabletop
Static- pushing a piece of furniture
and it not moving.
List the three types of Kinetic Friction
and give an example of each:
Sliding Kinetic Friction- moving a book across a desk, applying brakes in a car, scratching your
arm
Rolling Kinetic Friction- wheels of a bike, toy car, trains on a track
Fluid Kinetic Friction- oil lubricating parts on a plane, car, or bike, water flowing through a hose
Forces
Two young girls are fighting over a present. One is pushing is with a force of 10N to the right and the other is
pushing with a force of 50 N to the left. Use the picture below to answer the questions that follow.
1.The forces shown above are PUSHING / PULLING/ PUSHING AND PULLING forces.
2. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES.
3. The forces are EQUAL / NOT EQUAL.
4. The forces DO / DO NOT balance each other.
5. There IS / IS NO motion.
6. The net force is __________________ in _________________ (direction).
Forces
Two children are moving their wagon across the street. One is pulling the wagon to the
left with a force of 100N and the other is pushing the wagon with a force of 100 N to the
left. Use the picture below to answer the questions that follow.
1.The forces shown above are PUSHING / PULLING/ PUSHING AND PULLING forces.
2. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES.
3. The forces are EQUAL / NOT EQUAL.
4. The forces DO / DO NOT balance each other.
5. There IS / IS NO motion.
6. The net force is __________________ in _________________ (direction).
Friction
Force that opposes
motion between 2
surfaces
Depends on the:
■ types of surfaces
■ force between the
surfaces
Types of Friction
■ Static Friction:
(Couch Potato)
– Force between objects at rest
■ Sliding Friction:
(Ice skating)
– Solid surfaces slide over each other
■ Rolling Friction:
(Rollerblading)
– An object rolls over a surface.
■ Fluid friction:
(Submarine)
– An object moves through a fluid
Types of Friction
There are two types of friction:
◦Kinetic Friction: Friction between moving surfaces.
◦Kinetic means “moving”
◦Static Friction: When a force is applied to an object
but does not cause the object to move.
◦Static means “not moving”
Types of Friction
Two types of kinetic friction:
◦Rolling
◦Takes less force to roll an object than to slide it.
◦Ex. Anything that has wheels uses rolling kinetic friction
◦Sliding
◦Takes more force to slide an object than to roll it
◦Ex. Applying breaks to a bicycle, writing with a pencil,
scratching an itch
Friction
Friction is greater...
– between rough surfaces
– when there’s greater
force between surfaces
(such as more weight)
Lubricant
Changes sliding friction
into fluid friction
Friction
Is friction always bad?
Do Now
What is gravity?
Objective
Students will be able to utilize information from
friction in order to describe gravity and its
properties.
Agenda
Do Now
Test Next Friday (5/13)
Collect Do Nows
Friction Video
Gravity
Reminders for those
going on class trip…
ARRIVE AT SCHOOL AT 7
AM
Shorts fingertip length
Money for dinner
Wear comfortable
clothes
What causes friction?
Question:
Have you ever seen a video of astronauts on the moon? They
bounce around like beach balls even though they wear big,
bulky spacesuits. Why is leaping on the moon easier than
leaping on earth?
Gravity: the force of attraction between objects that is due to
their masses.
◦The force of gravity can change the motion of an object by
changing it’s speed, direction or both. There is less gravity on
the moon.
The Effects of Gravity on Matter
Remember: All matter has mass.
Gravity is a result of mass. Therefore, matter is affected by
gravity.
Because all matter is affected by gravity, that means all objects
experience an attraction toward all other objects.
◦Right now, because of gravity, you are being pulled toward
your book, your pencil, and every other object around you.
They are also being pulled toward one another.
Why don’t you feel gravitational pull
towards all objects around you?
The reason you don’t feel the attraction between you
and all other objects around you is that the mass of
most objects is too small to cause a force large enough
to move objects toward each other.
The earth is what causes those objects to seem like
they have no attraction to you at all.
The size of Earth’s gravitational force
Compared with all objects around you, Earth has a huge
mass. Therefore, Earth’s gravitational force is very large.
You must apply forces to overcome Earth’s gravitational force
any time you lift objects or even parts of your body.
Earth’s gravitational force pulls everything toward the center
of Earth. This is why objects that are dropped fall to the
ground instead of moving together or toward you.
Friction
How do we experience friction?
Newton and the Study of Gravity
It has been widely recognized that Isaac Newton
answered the following two questions (questions that
hadn’t been answered up until this time) while
watching an apple drop:
◦Why do objects fall toward Earth?
◦What keeps the planets moving in the sky?
The Core of Newton’s Idea
Newton knew that unbalanced forces are needed to
change the motion of objects.
He concluded that an unbalanced force on the apple
made the apple fall. From this he reasoned that an
unbalanced force on the moon kept the moon moving
circularly around Earth.
He proposed that these two forces are actually the
same force, the force of attraction called “gravity.”
The Birth of a Law
Newton summarized his ideas about gravity in a law
now known as the “law of universal gravitation.”
◦This law describes the relationships between
gravitational force, mass, and distance.
◦The law is “universal” because it applies to all objects
in the universe.
The Law of Universal Gravitation
All objects in the universe attract each other through
gravitational force.
The size of the force depends on:
◦ the masses of the objects
◦ the distance between the objects.
Gravitational Force Increases as Mass
Increases
The cat and the elephant:
◦The elephant has a larger mass than the cat. Therefore, the
amount of gravity between the elephant and the earth is
greater than the cat and the earth.
◦Because of the effect of gravity on their masses, the cat is
much easier to pick up.
◦There is also gravitational pull between the cat and the
elephant, but the mass of the elephant is so much smaller than
the earth’s mass, their gravitational pull is much smaller.
Gravitational Force Increases as Mass
Increases
This phenomena shows why astronauts bounce on the moon
and not on earth. The moon’s mass is much less than earth’s
mass so it’s gravitational pull is much less allowing the
astronauts to bounce more.
Gravitational Force Decreases as
Distance Increases
You jump up and land on the ground because of the
gravitational force between you and earth.
The sun is 300,000 times more massive than earth… so why
doesn’t the sun’s gravitational force affect you more than earth’s
does?
The reason is that the sun is so far away.
◦We are about 150 million kilometers away from the sun. If you
could stand on it, you would find it impossible to move AT ALL.
Weight as a Measure of Gravitational
Force
Gravity is a force of attraction between objects.
Weight: is a measure of the gravitational force on an
object.
◦Usually you hear weight referring to the Earth’s
gravitational pull on an object, but weight can also be
a measure of the gravitational force exerted on
objects by the moon or other planets.
Is there a difference?
Is there a difference between mass and weight?
The Differences Between Weight and
Mass
Weight is related to mass, but they are not the same.
◦Weight changes when gravitational force changes.
Mass: the amount of matter in an object.
◦The amount of mass in an object does not change.
This can get confusing… because weight and mass are
“constant” on Earth, the terms weight and mass are
often used to mean the same thing. Be sure you know
the difference!!!
Units of Weight and Mass
You have learned that the SI unit of force is a Newton
(N).
Gravity is a force, and weight is a measure of gravity.
So… weight is also measured in Newtons (n).
The SI unit of mass is the kilogram (kg). Mass is often
measured in grams and milligrams as well.
On earth, a 100g object, such as an apple weighs about
1 N.
Why Bathroom Scales Confuse Us
When you use a bathroom scale, you are measuring
the gravitational force between your body and Earth.
So you are measuring your weight, which should be
given in Newtons.
However, many bathroom scales have units of pounds
and kilograms instead of Newtons. Thus, people
sometimes mistakenly think that the kilogram (like the
pound) is a unit of weight.
Exit Slip
Why is it harder to pick up an 18 lb. bowling ball
as opposed to a baseball?
Do Now
What is the difference between mass
and weight?
Objective
Students will be able to analyze
and integrate information in order
to explain the law of universal
gravitation.
Agenda
Do Now
Test this Friday
Interim Reports Next Week
Video and Worksheet
Do Now
What is the law of universal gravitation?
Objective
Students will be able to analyze and integrate
information in order to explain the law of
universal gravitation.
Agenda
Do Now
Test Friday
Interim Reports Next Week
Expectations
Webquest
Expectations
Do not go on websites other than the one you
are supposed to be on
If caught, you will get point deductions, NO
COMPROMISES
If you get 3 point deductions, you receive a 0
Work in pairs only, with the pair you are seated
with, no exceptions
Do Now
Does the gravitational force change with
altitude?
Objective
Students will be able to analyze and integrate
information in order to demonstrate
knowledge of matter in motion.
Agenda
Do Now
Test Friday
Interim Report Next Week
Finish Gravity
Review Game/Chapter Review
Expectations
If you need anything, raise your hand
Do not get out of your seat
Do not tap your tap or pencils
Do not call out “Mr. Han” to get my attention, I will
get to you in the order I see your hands
Point deductions will be given if you are not following
the expectations
Gravitational Force Decreases as
Distance Increases
You jump up and land on the ground because of the
gravitational force between you and earth.
The sun is 300,000 times more massive than earth… so why
doesn’t the sun’s gravitational force affect you more than earth’s
does?
The reason is that the sun is so far away.
◦We are about 150 million kilometers away from the sun. If you
could stand on it, you would find it impossible to move AT ALL.
Weight as a Measure of Gravitational
Force
Gravity is a force of attraction between objects.
Weight: is a measure of the gravitational force on an
object.
◦Usually you hear weight referring to the Earth’s
gravitational pull on an object, but weight can also be
a measure of the gravitational force exerted on
objects by the moon or other planets.
Is there a difference?
Is there a difference between mass and weight?
The Differences Between Weight and
Mass
Weight is related to mass, but they are not the same.
◦Weight changes when gravitational force changes.
Mass: the amount of matter in an object.
◦The amount of mass in an object does not change.
This can get confusing… because weight and mass are
“constant” on Earth, the terms weight and mass are
often used to mean the same thing. Be sure you know
the difference!!!
Units of Weight and Mass
You have learned that the SI unit of force is a Newton
(N).
Gravity is a force, and weight is a measure of gravity.
So… weight is also measured in Newtons (n).
The SI unit of mass is the kilogram (kg). Mass is often
measured in grams and milligrams as well.
On earth, a 100g object, such as an apple weighs about
1 N.
Why Bathroom Scales Confuse Us
When you use a bathroom scale, you are measuring
the gravitational force between your body and Earth.
So you are measuring your weight, which should be
given in Newtons.
However, many bathroom scales have units of pounds
and kilograms instead of Newtons. Thus, people
sometimes mistakenly think that the kilogram (like the
pound) is a unit of weight.
Do Now
A car is moving downwards with a velocity of 5
m/s downhill and changes to 7 m/s downhill.
How do you know that the hiker has a positive
acceleration?
Objective
Students will be able to analyze and integrate
information in order to demonstrate
knowledge of matter in motion.
Agenda
Do Now
Collect Do Nows
Review/Prep.
Test
Expectations
If you need anything, raise your hand
Do not get out of your seat
Do not tap your tap or pencils
Do not call out “Mr. Han” to get my attention, I will
get to you in the order I see your hands
Point deductions will be given if you are not following
the expectations