Transcript DV_Matter-Teacher

Matter
Ms. Mitchell’s 6th Grade
Greenbriar West Elementary
2007-2008
TEACHER VERSION
Teaching Strategy
• Lecture
– Reinforce terms from SOL objectives
– Interactive – use handout as framework, not many answers
on the sheets – have students fill in during class
–
marks the sheets that only the teacher gets
• Simple Lab
– Provide blank graph for students to use
– Reinforce skills in observation, data plotting, and making
conclusions
Topics
• Mass
• Force
–
–
–
–
Gravity
Weight
Tides
Our Solar System
• Energy
– Potential Energy
– Kinetic Energy
• Power
Mass
• What is mass?
• Does a party balloon have more mass than a
candy bar?
• How do you figure out an object’s mass?
Mass
• What is mass?
– Matter or stuff
• Does a party balloon have more mass than a candy
bar?
– Bring in one of each; contrast size vs mass
• How do you figure out an object’s mass?
– Weigh it; but is mass the same thing as weight? No, will
talk about this in a moment; mass of something is the
same no matter what but its weight varies…
Force – Key Points
• What is a force?
• Why does gravity exert a force on you?
• If an object is not moving does that mean
that there are no forces on it?
Force – Key Points Answers
• What is a force?
– Something that pushes or pulls you
• Why does gravity exert a force on you?
– Two objects with mass attract each other
• If an object is not moving does that mean
that there are no forces on it?
– It may but it probably means that the forces
acting on an object cancel out
Forces
The cool car is in my driveway.
Are there any forces
on the car?
If so, draw them.
driveway
Forces
The force due to gravity
on my car is the same in size,
but opposite in
direction, to the force
by the driveway!!!!
Gravity
Driveway
Gravitational Force - Questions
• So what causes a gravitational force?
• Is there a gravitational force on the moon?
– Is it larger or smaller than the gravitational
force on the Earth?
Gravitational Force - Answer
• So what causes a
gravitational force?
– Two objects are attracted to
each other
Object 1 (has mass)
F1
F1 = F2
•Gravitational force
keeps us “stuck” to the
Earth!!!
•We actually pull on the
Earth but the Earth is too
massive to move!!!
F2
Person
F
Object 2 (has mass)
Fperson = Fearth
F
Earth
Universal Law of Gravitation
• F = m (GMe/Re2) = mg (i.e. weight)
– Where
•
•
•
•
•
F = force on an object with mass, m
G = gravitational constant = 6.7 x 10-11 m3/kg*s2
Me = mass of the Earth = 5.94 x 1024 kg
Re = radius of Earth = 6.38 x 106 m
g = acceleration due to gravity = 9.81 m/s2
• Circle the terms above that are constants
Universal Law of Gravitation
• F = m (GMe/Re2) = mg (i.e. weight)
– Where
•
•
•
•
•
F = force on an object with mass, m
G = gravitational constant = 6.7 x 10-11 m3/kg*s2
Me = mass of the Earth = 5.94 x 1024 kg
Re = radius of Earth = 6.38 x 106 m
g = acceleration due to gravity = 9.81 m/s2
• Circle the terms above that are constants
– But note that G is the only true constant because if
you go to another planet the other terms will vary…
Acceleration Due to Gravity
• There is a force exerted on an object as the result
of the mass of the Earth
– Therefore, the object is accelerated (I.e. the speed
increases) when released
At time = 0 seconds, an object is released with no velocity
One second later, it is going 9.81 meters/second
Therefore, the acceleration due to gravity is 9.81 meters/second
per second which is the same as 9.81 m/s2
Gravitational Force
• Gravitational force keeps us “stuck” to the
Earth!!!
• We actually pull on the Earth but the Earth is too
big to move!!!
Person
Fperson = Fearth
F
F
Earth
How much you
weigh depends on
your mass and the
mass of the planet
you are on.
Weight vs Mass
• Weight is a force: W = m g
PLOT THE DATA!!
m (kg)
W
(Newton)
10
98
5
49
12
118
5
52
18
177
5
47
8
78
Weight, Newtons
 m = mass and
 g = acceleration due to gravity = 9.81 m/s2
180
160
140
120
100
80
60
40
20
0
0 2 4 6 8 10 12 14 16 18 20
Mass, kg
Weight vs Mass
• The slope of the plot is g = 9.81 m/s2
– Slope is change in y over change in x
m (kg)
W
(Newtons)
10
98
5
49
12
118
5
52
18
177
5
47
8
78
Weight, Newtons
• Change in weight divided by change in mass
180
160
140
120
100
80
60
40
20
0
X
X
X
X
X
X
X
0 2 4 6 8 10 12 14 16 18 20
Mass, kg
Review of Science Terms
• Constant – _____________________________
• Variables – _____________________________
• Independent Variable – ___________________
• Dependent Variable – ____________________
Review of Science Terms
• Constant – item that does not change
• Variables – things in an experiment that change
• Independent Variable – variable that is changed
• Dependent Variable – variable that is measured (it
“depends” on the other settings)
Gravitational Force - Questions
• Is there a gravitational
force on a person
standing on the moon?
– Is it larger or smaller
than the gravitational
force on the Earth?
– Why?
Gravitational Force Answers
• Is there a gravitational force on the moon?
– Is it larger or smaller than the gravitational
force on the Earth? yes
• The gravitational force is smaller on the moon – 1/6
of the Earth.
– Why?
• The moon is smaller (1/6th the mass) than the Earth.
How the Moon Causes Tides
• Since the water in the oceans are liquid they are
pulled out of shape by the moon’s gravitational
force
– Causes water level to rise thus creating tides (i.e. water
seemingly getting deeper and shallower for no apparent
reason)
Water bulging up
Earth
Moon
Our Solar System
• The Sun is the center of the solar system
– Why is it the center?
– Why is it useful to have the Sun as the center?
• Nine planets orbit the Sun
– Inner planets are small and rocky
• What are they?
– Outer planets are large and gaseous (mostly)
• What are they?
Our Solar System
• Inner Planets
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–
–
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Mercury
Venus
Earth
Mars
• Which planet is hottest?
• Which planet is coldest?
• Does this make sense?
• Outer Planets
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–
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Jupiter
Saturn
Uranus
Neptune
Pluto
• How do you think Pluto
was added to our solar
system?
Inner Planets
• The time it takes for a planet to orbit the Sun (i.e. orbital period)
is proportional to how far the planet is away from the Sun.
– Will it take more or less than a year for Venus to orbit the Sun?
Asteroid Belt
•
Asteroids are rocky and metallic objects
that orbit the Sun but are too small to be
considered planets.
– Range in size from pebbles to as large as
1000 km
– Sixteen asteroids have a diameter of 240
km or greater.
•
Most asteroids are contained within a
main belt that exists between the orbits
of Mars and Jupiter.
– Some have orbits that cross Earth's path
and some have even hit the Earth in
times past.
•
Asteroids are material left over from the
formation of the solar system…
Outer Planets
- How do the outer (or Jovian) planets differ from the
inner (or terrestrial) planets?
Planets By Size !!!!!!
• Mars is the same mass as Earth but half the size – what does that tell you
about the density of Mars?
• Jupiter weighs more than any other planet – twice as heavy as the nest most
massive (Saturn).
– On which planet would you weigh the most – or would you weigh the same on
every planet?
Potential and Kinetic Energy
• What is energy?
• What is potential energy?
• What is kinetic energy?
Potential and Kinetic Energy
• What is energy?
– Ability to do work
• Potential energy – “stored” energy
– How can we “store” energy?
• Kinetic energy – energy of movement
– How is potential energy converted into kinetic energy?
Potential Energy
Does the box
have any stored
energy here?
Does the box
have any stored
energy here?
Potential Energy
Does the box
have any stored
energy here?
Does the box
have any stored
energy here?
NO
YES, we moved the box
against gravity (did work)
Potential Energy
What happens when we let go
of the box?
If the box is to move show the
direction of the box.
Label the forces on the box!!!!
Potential/Kinetic Energy
Gravity
velocity
What happens when we let go
of the box?
It starts to fall – has kinetic energy
Convert potential into kinetic energy
If the box is to move show the
direction of the box.
Air
Label the forces on the box!!!!
resistance
Gravity is larger force than
air resistance
Work, Energy, and Power
• Review: Force is a push or a pull
– Exerting a force over a distance is WORK
• For example, pushing the desk across the room is “a lot of work”
– ENERGY is the ability to do work
• For example, a compressed spring has the ability to push some object
a distance
– POWER is the consumption of energy over time
• For example, power is consumed when a light bulb is left on for a
period of time (light bulb dissipates energy)
Quick Review of Science Facts
• Force - ___________
• Work - ___________
____________________
• Energy - __________
___________________
• Power - __________
___________________
___________________
• Constant – ___________
______________________
• Variables – ___________
_______________________
• Independent Variable –
_____________________
• Dependent Variable – ___
_______________________
_______________________
Quick Review of Science Facts
• Force - a push or pull
• Work - exerting a
force over a distance
• Energy - the ability to
do work
• Power - energy being
used over a period of
time
• Constant – item that does
not change
• Variables – things in an
experiment that change
• Independent Variable –
variable that is changed
• Dependent Variable –
variable that is measured (it
“depends” on the other
settings)