Transcript Work Equation

Hello my dear Students,
As you can see I am not here today. I will be back
tomorrow so please don’t shed too many tears
for me. I know its tough but I’m sure you can do
it. I believe in you!
Put all jokes aside, it is crucial for you to
complete everything (both classwork and
homework) that I have left for you as we will not
have extra class time to spend on them.
I expect everything I have left to be done when I
see you next.
You will be at your best behavior today . I am
looking forward to hearing great feedbacks from
your sub .
Homework:
2nd and 3rd Block:
1. Read and annotate pages 156, 157, and 168.
2. Finish the 7th Grade SOL Packet.
3. “Newton's Laws of Motion” Quiz next class.
4th Block:
1. Complete pages 7-9 of the SOL packet.
2. “Newton's Laws of Motion” Quiz next class.
Essential Question (pg. 135):
What is friction?
Friction is the force that opposes
motion between any two surfaces
that are touching.
What creates friction:
It happens when two surfaces rub
against each other.
Essential question (pg. 129): What is
force?
• Energy that is created by a push or a
pull
What is inertia:
• Object’s resistance to change in
motion
• (objects are lazy and stubborn, if they
are stationary they want to stay
stationary; and if they are moving they
What is the S.I. unit for force?
Newtons (N)
How it affects Balanced
….
Forces
Motion
Keeps the
object
moving
Acceleration No
acceleration
Net Force
Velocity
0
Constant
velcity
Unbalanced
Forces
Slows down
or stops the
object
Increase in
the direction
of larger
force
>0
Increase in
the direction
of larger
force
Page 131
Newton’s first law of motion:
Car driving down the road:
• inertia: - car keeps on moving unless it is
stopped by outside forces
Car sudden stop (hitting a tree/ sudden break):
• The person in the car wants to continue moving
at the speed the car was moving.
Explanation of observation:
• The seat belt exerts a force against the person’s
body to stop them from moving forward and
flying off the seat.
Car at rest (stop sign):
• Inertia- car at rest wants to stay at rest until
moved by an outside force.
Car being hit from behind:
• When a stopped car begins moving quickly,
you are pushed back against the seat. The
body is at rest, but the moving car exerts a
force and changes this.
Explanation of observation
• If there was no “head rest” then the neck
would snap back very hard causing a
whiplash.
Newton’s second law of motion
How force affects acceleration:
• The amount of force applied to
two objects with the same mass
will cause them to accelerate
differently.
• more force will make the object
move faster.
How mass affects acceleration:
• If the same force is applied to
two objects with different
masses, the lighter object will
accelerate faster.
Newton’s Third law:
Observation: When a tennis ball
hits the floor it exerts force on the
floor (action) – the floor reacts by
pushing the ball up with the same
force (reaction)
Reason: for every action there is
an equal and opposite reaction.
What factors affect the amount of
friction between two surfaces?
• Texture of surfaces
• Force that pushes the surfaces
together
Your Question:
Why does friction occur?
It occurs because no surface is
perfectly smooth (all surfaces are
bumpy, therefore the “mountains and
valleys” get get stuck into each other)
Essential Question (pg. 137): What
are the different forms of friction?
• Static friction
• Kinetic friction (sliding friction,
rolling friction, fluid (liquids and
gases) friction )
Which is greater, static or kinetic
friction?
Static friction is greater because it
keeps objects from moving.
What are all the types of friction a
swimmer experiences diving through
the water?
Kinetic friction ( fluid friction and
sliding friction)
What is fluid friction?
When two surfaces rub against each
other and one of the surfaces is a
fluid (gas or liquid)
Essential Question (pg. 139): What
causes falling object to fall?
Gravity
Which planet has the greatest
acceleration due to gravity and why?
Jupiter, because it has the lowest
mass (gas giant, mostly made of
gases)
What happens to the gravitational
force between two bowling balls if
they were moved farther apart?
They gravitational force between them
would decrease, because the
distance between them increases.
Your Question: What are the two
factors that affect gravity?
• Mass of different objects
• Distance between the two objects
Essential Question (pg. 151): What
counts as work?
• Work means the use of force to move
an object in the same direction as
force.
Explain why pushing on a building is not
work even though you may get tired.
• Pushing a building is not considered
work because the building does not
move no matter how much you push it.
Why isn’t carrying a box down a
hallway considered work?
It is considered work because
force applied to lift the box is NOT
in the same direction as the box
moves.
Work Equation
Work = Force x distance
w=Fxd
Equation Symbol S.I. Unit
Symbol Meaning
W
Work
Joules
(J)
F
Force
Newtons
(N)
d
Distance Meters
(m)
Essential Question (pg. 153): How
does increasing the power affect
work and time?
• More work in the same amount
of time
• Same amount of work in shorter
time
What are the S.I. units for power?
• J/s or Watts
Explain how a 10 W motor in
blender and a 20 W motor in a
blender do work differently.
• It will take longer for a 10 W
blender to do the same amount
of work as a 20 W blender.
Power Equation
Power = Work / Time
Equation
Symbol
P
W
t
Symbol
Meaning
Power
Work
Time
S.I. Unit
Watt or J/s
Joules
S
Essential Question (pg. 159): How do
machines help us?
• They make work easier by taking our
work and changing it to a job.
What three things do machines do?
• It takes an input work and
manipulates it by either increasing
the force, distance, or changing the
direction the force is going to be
applied.
Explain why machines do not lessen the
amount of work you need to move a load?
They change the way work is done.
They either:
• Increase the amount of force
applied
• Increase the distance over which
force is applied
• Changes the direction the work is
applied
Essential Question (pg. 169): What are
some types of simple machines?
• Lever, Pulley, inclined plane, wheel
and axle, screw, wedge
When will a wheel an axle have a
mechanical advantage greater than
one?
• When the input force is applied to
the wheel, because the machine
multiplies the input force.
How do screws help us do work?
Screws are inclined plane
wrapped around a cylinder.
They move objects to a greater
depth (or higher elevation) by
increasing the force applied to
the screw.
Your Question: What is an inclined
plane?
• It’s a simple machine that consists
of a sloping surface connecting a
lower elevation to a higher
elevation.
• It makes work easier by applied
force over a longer distance.