Transcript Forces

Forces
On a post-it, write down anything
you know about the word force or
the different ways you use the word
force.
Scientific Definition
• A force is a push or a pull of an object.
• When there is a force, one object is applying a force and on
object is receiving the force.
Characteristics Used to Describe a
Force
1) Magnitude (size)- the amount of force being
exerted
2) Direction- the direction in which the force is
moving the object
Effects of a Force on An Object
MOTION!
-start moving
-stop moving
-speed up
-slow down
-change directions
Identifying Forces
• Some forces are obvious, because you see
where the force is coming from since they act
based on touch.
• Some forces are not obvious because they can
act with out touch.
– GRAVITY
– MAGENTS
– -STATIC
Measuring a Force
• The unit used to measure how much force an
object is exerting is the Newton.
– The abbreviation for Newton is N.
– One Newton can lift one small apple.
• The tool used to measure force is a spring scale.
• The more mass an object has, the
more force it will require to move
the object.
• As mass increases, force increases.
Combining Forces
• Sometimes there is more than one force being
exerted on an object
• The forces being exerted may be working in the same
direction.
• Example: a plane traveling in the same direction as the
wind
• Sometimes there are multiple forces acting on
an object in different directions.
– Example: a plane flying against the wind
Think, Pair, Share:
Name all the forces acting on the kite.
Are all the forces working in the same direction?
Net Force
• Net force is the combination of all the measure of
all the forces being exerted on an object.
• In order to determine the net force when the
forces are acting in the same direction, you add up
the measure of all the forces.
• Example: My sister and I are moving a piano
together in the same direction. I exerted 15
Newtons while my sister exerted 10 Newtons.
What is the net force applied to the piano?
•
______ N to the ___________ (direction)
Net Force: Different Directions
• To determine the net force on an object with
forces acting in different directions, you subtract
the smaller force from the bigger force.
• When there are forces working in different
directions, it will lessen the force on the object.
Net Force
What does net force tell us?
• if the object will move
• in which direction the object will move
• how strong the force is on the object
Balanced Forces
• A balanced force is produced when two forces are acting in different
directions and are equal, which means the net force is 0.
• When the forces applied to an object produce a net force of zero,
the forces are balanced.
• Balanced forces don’t cause movement in an object.
• Balanced forces will not change the motion of a moving object.
Unbalanced Force
• When the force of an object is not zero, then it is an
unbalanced force.
• An unbalanced force is when one force is stronger
than another force.
• An unbalanced force causes a change in the
movement of an object.
1. start/stop movement
2. change direction of movement
3. speed up/ slow down movement
Picture Walk
Choose a picture with your group. Then discuss
and answer the following questions on an index
card. Be ready to present the information to the
class.
1. What are the forces being exerted on the
object?
2. Are the forces balanced or unbalanced?
3. What are the effects of the force?
4. How would you determine the net force being
exerted on the object?
Friction
• Question: When you kick a soccer ball,
eventually it will stop moving. Why?
Description of Friction
• Friction is a force that appears whenever two things rub
against each other.
• Friction always works in the opposite direction of the
force being exerted on the object. Therefore, it affects it
slows down its movement and eventually causes the
object to stop moving.
– Example: force of kick causes ball to move in one direction,
while friction is slowing down the movement of the ball and
eventually slowing it down.
• Even though a surface may seem smooth, it actually has
tiny bumps that can be seen with a microscope. Therefore
all surfaces cause friction.
Friction Depends On:
1. mass: objects that have more mass push
harder and closer against the surface and
therefore cause more friction.
1. surface: Objects with smooth surfaces cause
less friction. Objects with rough, bumpy
surfaces cause more friction.
Exit Ticket
• What do you think would happen if you kick a
ball in space? Why?
• How does friction affect the force exerted on
an object?
Four Types of Friction
1) rolling friction- when one object ROLLS over
another object, usually on wheels
Examples: bike, car, stroller, ball , train,
rollerblading, skateboarding
2) sliding friction- friction used when one surface
slides past another surface
Examples: writing, walking, itching your skin,
pushing a book, touching something
Which of he two produce more friction?
(think of a suitcase)
3) fluid friction- any friction that occurs between a liquid or
a gas and an object
Examples: objects in water, objects in air
4) Static friction- the friction that occurs between two
objects when object applies a force on another object but
the object does not move. Static friction disappears once
the object begins to move.
Example: when you push something heavy but it does not
move, static friction occurs. Once it moves, static friction
disappears and sliding friction occurs.
Is friction a good thing or a bad thing?
positive effects
• friction between floor and feet helps us walk
• car brakes, tires pushing against the floor to move
• holding anything in your hand would be difficult without
friction- writing
• sports- cleats for softball, gloves for better grip, sneakers
negative effects
• car parts rub together causing engine parts to heat up
and be worn down
• holes in socks, clothing, shoes worn out from friction
• friction by water and wind causes erosion/rust –bike in
rain
Increasing/Decreasing Friction
decreasing friction:
• adding wheels
• adding liquids
• lubricant-oil, wax, grease, air
• making the surface smoother (sandpaper)
increasing friction:
• make surfaces more rough (brillo, salt, gloves)
• add mass
Exit Ticket
• Based on what we learned today, explain why
a ballerina wears ballet slippers.
• Why is friction good for a car? Bad for a car?
What do you already know about
gravity?
Record what you know about gravity on a post
it. Then post it onto the board.
What is gravity?
• Gravity is a force of attraction between two
objects.
• All objects with mass have a gravitational force.
The gravitational force pulls objects towards
each other.
• The force of gravity can affect the motion of an
object by changing its speed, direction or both.
Gravity depends on:
1) mass- the more mass an object has, the more
gravitational force it will have. (Example: you
and the desk vs. you and Earth.)
2) Distance- the closer two objects are to one
another, the greater the gravitational force.
Isaac Newton
• British scientist named Isaac Newton realized
while watching an apple fall from the tree that
there has to be some unbalanced force that is
causing the apple to move.
• He came to the conclusion that the force was
gravity which is pulling everything on Earth
towards Earth.
• This became known as the law of universal
gravitation- it is a law because it applies to all
things in the universe.
Effects
• What are some effects of gravity on you?
• What would happen without gravity?
Review: What is the difference
between weight and mass?
• Mass- the measure of how much matter is in an
object
• weight-the measure of gravitational force on an
object
• Mass never changes, but weight changes
depending on how much gravitational force there is
on the object.
• You weigh less on the moon than you do on Earthwhy?
• Why is there less gravity on the moon?
Directions
• You will get into groups of 4 and choose roles.
–
–
–
–
pens/pencils keeper
teacher getter
clarifier
coordinator /point keeper
• You will discuss the answers to each of the questions based on what
you learned about gravity. While you discuss, all pens/pencils must be
placed in the bin.
• After you discuss the answers, each student will write down the
answer to the question on a post-it and place it underneath the
question they answered.
• If one person has a question, then all students must put their
pens/pencils down to discuss and answer the question.
• Reminders:
– Do now write any of the answers in your notes
– When there is talking there is no writing When there is writing there is
no talking.
Use the picture to help answer the
questions.
How does gravity affect the tides?
•The side of the Earth that is facing the mood has a high tide and the
opposite side has a high tide because graity is pulling the water tiwards the
moon.
•The sides that are not facing the moon are expeiencing low tide.
•Th