Transcript Chapter 2: Kinematics in One Dimension

Ocean Science!
• Monday
– Review 20-2 reading guide questions.
– Review for tomorrow’s quiz
– Start frozen seas video
• Tuesday
– 20-2 Ocean Life Quiz
• Wednesday
– Research questions
– Finish Frozen seas video
• Thursday
– Ocean resources
• Friday
– Ocean Resources
Improvements
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Needs reordered according to gravity notes for real.
Yes, definitely needs reordered
Look up common misconceptions & address them
Use physics website more!
More on weight…students never get how to calculate weight! Is important
later too.
Weight on other planets!
Make peanut butter jars with different weights for different gravity!
It’d be coolest if it were a regular weight on Earth!
Bonus!
• The acceleration due to gravity on the
“surface” of Jupiter is 25.9 m/s2. How
many pounds would a 80.0 kg person
weigh there?
(1.00 lb = 4.46 N)
Bell Work 4/8/13
New Bell Work Sheet!
1. How many Newtons would a 885.0 kg object
weigh on Earth’s surface? (Use F = ma, a =
9.81 m/s2)
2. Convert this to lbs.
Bell Work 4/22
1. A 45.0 kg ball experiences a force of
441.45 N. What will it’s acceleration be?
2. A 90.0 kg ball experiences a force of 882.9
N. What will it’s acceleration be?
3. W5SAYWoS
• Wednesday
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Update grades
See quizzes?
Review labs
Law of gravity notes!
• Thursday
– Law of gravity notes!
Schedule
• Turn in your newton’s laws demos lab!
• Make sure your grade sheet update!
Show me for some pts!!! 10 pts!!!!!
Today you are going to…
take notes on gravity!
So you can…
explain what affects the force of gravity & predict the
gravity between different objects
You’ll know you’ve got it when you can
• Answer the questions at the end of slide show
The 4 Fundamental Forces
Gravity!
• What does it do?
– Holds objects on Earth
– Makes objects fall
– Keeps satellites in orbit!
Gravity!
• Gravity is the attraction between any two
objects that have mass.
• It’s actually the weakest force!
• It’s magic!!
– We don’t really understand it (but then, that’s
true of most fundamental stuff)
• Sir Issac Newton wrote the law of
universal gravitation.
Gravity & Mass
• Universal gravitation equation 
G = 6.67 x 10-11
• 2 things affect the force of gravity:
___________ and _____________
• The force of gravity is
___________________ related to mass.
Gravity & Mass
• Gravity is the attraction between any two objects that
have mass. Why don’t we notice the force of gravity
between all objects?
6.67 x 10-11 (50 kg)(5.97 x 1024 kg)
(6,371,000 m)2
491 N = 110 lbs
6.67 x 10-11 (50 kg)(1.0 kg)
(1 m)2
3.35 x 10-9 N
0.000 000 003 35 N = 0.000 000 000 754 lb
• Gravity is the attraction between any two objects that
have mass. Why don’t we notice the force of gravity
between all objects?
Even though the force of gravity between less massive
objects is, it would be noticeable if it were the only force
around.
However, on Earth the gravity of Earth overpowers these
other gravities, not to mention the fact that the gravity
between you & other objects are pulling in all sorts of
directions, so they cancel out.
Far away from planets, the gravity of semi large objects
would have an effect. It’s one way we could deflect an
oncoming asteroid!
Gravity & Distance
• Universal gravitation equation 
G = 6.67 x 10-11
• The force of gravity is
___________________ related to distance.
Gravity & Distance
• The force of magnetism
• Which is stronger, gravity or magnetism?
• How are gravity and magnetism similar?
• How are gravity and magnetism different?
Gravity, Mass, & Distance
What happens to the force of gravity if:
mass doubles?
distance doubles?
So gravity depends more on ___.
What’s this table tell you?
• Would your mass or weight be any different
on the moon? Why?
• Would your mass or weight be any different
on the top of a tall mountain? Why?
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What is the weakest fundamental force?
Who discovered the law of gravity?
What 2 things does the force of gravity depend on?
Which does it depend on more?
The force of gravity is directly related to ___, and you
can tell because ____
• The force of gravity is directly related to ___, and you
can tell because ____
• You would weigh ___ on the moon because _____.
• You would weigh ___ on Mt. Everest because _____.
Today you are going to…
take notes on weight & freefall
So you can…
calculate weight
explain how objects freefall
explain the behavior of projectiles
You’ll know you’ve got it when you can
• Answer the questions at the end
Bell Work 5/5/14
Do 1-7 on the Gravity and Projectile Motion Study
Guide #1
Free Fallin’ Tom Petty
https://www.youtube.com/watch?v=jVa0sISCjXc
Freefall!
• Freefall - when gravity is the only force
acting on an object.
• All things on Earth’s surface fall with same
acceleration (_______).
• If 2 objects were both dropped from the
same height, they would hit the ground at
the same time. Why don’t we notice this?
• Strobe light & drops of water!
Air Resistance!
• Air resistance keeps all objects from falling
with the same acceleration on Earth.
• Terminal velocity – the fastest an object
can fall due to air resistance
– Happens when force of air resistance = weight
• FNET = 0, therefore a = _______!
• Moon Hammer Drop
• Feather in vacuum
• Elephant and feather on physics classroom
7 Minutes of Terror
• Landing
– 13,000 mph to 0 mph in 7 min
•
https://www.youtube.com/watch?v=Ki_Af_o9Q9s
• What are some differences between Earth
and Mars that
affect how things
fall there?
• Jill and Nick have a task. They both have to push a cart
down the hall with an acceleration of 5.0 m/s2.
• Jill’s cart has a mass of 10.0 kg. How hard does she
have to push it?
• Nick’s cart has a mass of 20.0 kg. How hard does she
have to push it?
• Even though Nick pushes his cart twice as hard, his cart
accelerates at the same rate because…
Freefall!
• Why do all things fall with the same acceleration?
Shouldn’t heavier objects fall faster?
• Earth’s force of gravity on an object is its weight.
• On the surface of Earth: 1.0 kg weighs about 9.81 Newtons.
• A 5.0 kg object weighs 44.05 Newtons. Calculate its
acceleration when dropped.
• A 10.0 kg object weighs 98.1 Newtons. Calculate its
acceleration.
Why is the acceleration for
everything the same?
• If something has twice the weight, it also
has twice the inertia, therefore it’s twice as
hard to accelerate.
• Gravity is like horse drawn carriages, or a
bunch of tiny magnets!
• Would two pieces of clay fall faster if
combined?
Bell Work 4/25/13
1. What 2 things determine the strength of the
force of gravity?
2. Do all objects fall with the same acceleration
on Earth’s surface? Why/Why not?
3. Do objects with twice the weight fall with the
same acceleration? Why/Why not?
4. Which falls faster, a bullet that’s fired
horizontally or a bullet that’s dropped? (or
neither)
Weight
Weight Weight don’t tell me!
• Weight - force of gravity between an object &
a planet.
• FW = ma
(a is acceleration due to gravity)
• How much would a 1.00 kg object weigh on
the surface of Earth? In lbs?
Today you are going to…take notes on projectiles and
circular motion.
So you can…predict and explain the motion of
projectiles & objects in circular motion
You’ll know you’ve got it when you can
• Accurately answer the questions
Monday
Schedule
Gravity Notes & Questions
Tuesday
Projectile & Circular Motion Notes & Questions
Wednesday
Orbits!
Thursday
Review Questions & Begin Egg Drop Project
Friday
Build Egg Drop Project
7 Minutes of Terror
• Landing
– 13,000 mph to 0 mph in 7 min
•
https://www.youtube.com/watch?v=Ki_Af_o9Q9s
• What are some differences between Earth
and Mars that
affect how things
fall there?
Free Fall & Reaction Time
• http://www.brianmac.co.uk/rulerdrop.htm
Projectile Motion
Projectile Motion
• Projectile motion – motion in which an object
(projectile) is thrown near a planet’s surface,
and gravity is the only force acting on it
– Ex. Thrown football, bullet shot, cow launched
from catapult.
• Projectiles follow curved path called a
parabola.
Projectile Motion
• Projectiles are in freefall!
Projectile Motion
• has horizontal (left & right) & vertical (up &
down) motion.
• The horizontal and vertical motion are
independent.
– They don’t affect each other!
• Which will hit the ground first, a bullet fired from
a gun or a bullet dropped from the same
height?
• Mythbusters!!
• http://www.youtube.com/watch?v=D9wQVIEdK
h8
Horizontal Projectile Motion
• The horizontal (Vx) velocity of a projectile
doesn’t change!
– This makes sense because the net force in that
direction is ____________.
Vertical Projectile Motion
• A projectile
– takes as long to go up as it does to come down
to the same point at which you released it.
– It will be going the same speed in the opposite
direction when it reaches its original height.
– At its maximum height:
• vy =
• t=
Projectile Motion
• What 2 things affect the distance of a
projectile?
• What angle will launch a projectile farthest?
• What angles will launch projectiles the same
distance?
Bell Work 4/26/13
1. What is the shape of a projectile?
2. What angle will launch a projectile farthest?
3. What angles will launch projectiles the same
distance?
4. List 3 things that affect the range (distance) of
a projectile.
Projectiles with Air Resistance
• The optimal angles to send balls flying the
farthest distances are around 40°. For
example, for kicking or punting a football,
you yield the largest distance at a launch
angle between 35° and 40°. If you throw a
small ball, such as one used in track and
field events or a baseball, the ball is much
smaller. Thus, the friction plays a smaller
role in the movement. Then the best angle
is almost 45°.
Projectile Motion
Shoot a Monkey!
• http://www.youtube.com/watch?v=cxvsHN
RXLjw
Citing a rifle in
• Can an object be moving upwards if
nothing is pushing it?
• Can an object be moving horizontally if
nothing is pushing it?
• Is force required to keep an object in
motion? (Newton’s ______ Law)
Bell Work
• Which direction do you think the doughnut
will travel when the string breaks?
Monday
Schedule
Check HW (Study guide), Review questions, Egg Drop
Tuesday
Notes on Circular Motion & Orbits
Egg Drop
Wednesday
Notes on Orbits & Weightlessness
Egg Drop
Thursday
Review Questions & Finish Egg Drop Project
Friday
Test Egg Drop Project
Today you are going to…take notes on circular motion.
So you can…understand the direction of acceleration &
velocity in circular motion and “centrifugal” force.
You’ll know you’ve got it when you can
• Accurately answer the circular motion questions.
Circular Motion
Circular Motion
• Objects in circular motion are accelerating
towards the center
• Centripetal force – force acting on an
object in circular motion; pulls towards
center of circle
Circular Motion
• Shape of horizontally thrown projectile
Centripetal Force
• Force diagram of object in circular motion
The forbidden F word!
• Centrifugal force – imaginary center
fleeing force on an object in circular
motion
• NOT REAL
• Caused by inertia…the object wants to
keep traveling in a straight line
Car driving in circles
The forbidden F word!
• Circular motion demos
• Why does it stay there? (a law)
• What force acts on it? What direction?
Demos & Puzzles
What provides the force
• Tom’s puzzle
• Penny in balloon
• Marble & tape
• Ball on string
• Color changing ball
• Ball on string through tube with weight
• Question: A ball is being whirled around by
a string. If the string suddenly breaks (or is
let go), what direction will the ball travel; A,
B, C, or D? (Neglect gravity) HAMMER
THROW!!!
Doughnut on a string!
• http://www.youtube.com/watch?v=TniQtoa
pVrQ&feature=related
• Answer: Path ___
• While attached to the string, the ball is
forced to follow a curved path. But once
the string is gone, no force is exerted and
(law of inertia) it follows a straight-line
path.
Bell Work 5/1/13
Answer questions 1-5 on the back of your
Gravity & Projectile Motion Study Guide.
Today you are going to…take notes on orbits!
So you can…understand how satellites, moons, and
planets orbit things.
You’ll know you’ve got it when you can
• Accurately answer the questions.
Projectile Motion & Orbits
Projectile Motion & Orbits
• Force diagram of object in circular motion
– (this should be earlier in slide show, when
circular motion first mentioned)
Projectile Motion & Orbits
• Objects orbiting Earth are in free fall!
– They’re falling!
– Gravity acts as the centripetal force
– Cannonball!
Satellites!
Earth Satellites
Earth satellite - projectile moving fast enough to fall
continually around Earth rather than into it.
The orbital speed for an object closely orbiting Earth is
about 8.0 km/s. That is 29,000 km/h (18,000 mi/h).
Earth Satellites
In the curvature of Earth, the surface drops a vertical
distance of nearly 5 meters for every 8000 meters
tangent to its surface.
Earth Satellites
For a satellite close to Earth, the time for a complete orbit
around Earth, its period, is about 90 minutes.
Earth Satellites
A satellite must stay 150 kilometers (94 miles) or more
above Earth’s surface. Why can’t we put a satellite into
orbit at low altitudes on Earth?
A satellite in circular orbit close to Earth moves
tangentially at 8 km/s (5 mi/s). During each second, it
falls 5 m.
Escape Velocity
To escape Earth’s gravity, an projectile must be
launched at a velocity of 11.186 km/s = 25,000 mph.
Rockets aren’t projectiles…they don’t need to go this fast.
The firing of the rocket provides a constant force.
Pioneer 10, launched from Earth in 1972, escaped from
the solar system in 1984 and is wandering in interstellar
space.
Space Junk!
Bell Work 4/8/11 – 4 minutes
1. Convert the following weight to Newtons.
A. 16 lb bowling ball
Find the mass of the above in kilograms.
2. Explain how satellites orbit Earth.
Bell Work
1. Get your notes & study guide out & finish the
last questions.
Schedule
Monday
Gravity Notes & Questions
Tuesday
Circular motion! Build Egg Drop Project
Wednesday
Orbits! Build Egg Drop Project
Thursday
Review Questions & Build Egg Drop Project
Friday
Review & Build Egg Drop Project
Monday
Test!
Tuesday
Test Egg Drop Project
Weightlessness!
Weight & Weightlessness
• How would it feel to be weightless?
• How do you feel your weight?
Circular Motion & Gravitation
87
Weight & Weightlessness
• What you feel as your “weight” is a
sensation due to the normal force
• Just because you don’t feel your weight,
doesn’t mean you’re weightless!
• Astronauts in space are not really
weightless.
Circular Motion & Gravitation
88
Weight & Weightlessness
• Astronauts are just in constant freefall!
Nothing is holding them up. They feel no
normal force, so they feel weighless. They
float in the space station because the
space station is falling with them.
• Since there’s nothing holding them up,
they feel weightless!
• Drop Han Solo!
Circular Motion & Gravitation
89
Weight & Weightlessness
Circular Motion & Gravitation
90
Would you like to be weightless?
Zero-G
• People On Vomit Comet
• http://www.youtube.com/watch?v=N6ZJnIJ
RUCI&feature=related
• Water balloons in zero gravity
http://www.youtube.com/watch?NR=1&fea
ture=fvwp&v=gTqLQO3L4Ko
end
Freefall on planets
What all is the same on the surface of Earth?
Figure out that everything else must be equal to
acceleration due to gravity.
Egg Drop!
• You may purchase more materials during project.
• Materials list (5 pts)
– Include quantity, description, price, total price, and net price.
– Explain the purpose/advantage of each material
– Don’t spend it all. You may purchase more materials during project.
• Blue print (10 pts)
– Anyone looking at the blueprint should be able to build it
– Everything must be to scale (1in = 1 square)
– Explain how things are attached, lengths of string
• Newspaper:
• Half Sheet 11.5” x 22.7” Full sheet 22.7” x 22.7”
• Don’t break your egg!
– If you do, you will have to clean it up.
• Make sure to calculate average speed & show all work.
• Winners get a free homework pass!
Materials List
#
2
6
2
Item
Full sheet of newspaper
Straws
12” pieces of tape
Cost
Net Cost
Total
Egg Drop!
• Answer the following questions in complete sentences on
your graph paper.
1. Explain how your design relates to what you know about air
resistance and freefall. How is it going to cause the egg to
fall slowly?
2. If you had to name a possible problem with your contraption,
what would it be? (What might go wrong?)
3. Hopefully your egg stopped accelerating pretty soon after you
let it go. What 2 forces were equal at this point?
4. If there were 2 eggs in your basket, would it have fallen
faster? Why or why not?
5. Were there any problems with your project? How could you
improve upon it (even if there weren’t problems)?
Bell Work 4/11/12
1. What is a satellite?
2. What are the forces acting on a satellite?
3. How long does it take a satellite to orbit
Earth?
4. Can we see satellites with the naked eye?
5. How fast do you have to throw a ball to
throw it off of the planet?
• Pluto has a mass of 1125 x 1022 kg and an
equatorial radius of 1195 km. (a) Calculate
the acceleration due to gravity on the surface
of Pluto. (b) A python weighs 980 N on Earth.
How much would it weigh on Pluto?
MP = 1024 kg
rP = 1195 km = 1195000 m = 1.195 x 106 m
G = 6.67 x 10-11 N m2/kg2
WE = 980 N
gE = 9.8 m/s2
gP = 0.59 m/s2
WP = ? N
g = G MP/rP2
g = (6.67 x 10-11)(1024)/(1.195 x 106 )2
g = 4.78 x 10-20 m/s2
WE = mgE
980 = m(9.8)
100 kg = m
W = mg
= (100)(4.78 x 10-18m/s2
= 4.78 x 10-18 N
• The elephant and the feather each have the same force of gravity.
• The elephant has more mass, yet both elephant and feather
experience the same force of gravity.
• The elephant experiences a greater force of gravity, yet both the
elephant and the feather have the same mass.
• On earth, all objects (whether an elephant or a feather) have the
same force of gravity.
• The elephant weighs more than the feather, yet they each have the
same mass.
• The elephant clearly has more mass than the feather, yet they each
weigh the same.
• The elephant clearly has more mass than the feather, yet the
amount of gravity (force) is the same for each.
• The elephant has the greatest acceleration, yet the amount of
gravity is the same for each.
Bell Work 4/8/11 – 5 minutes
1. Convert the following weights to Newtons.
A. 16 lb bowling ball
B. 17 lb cat
C. 20,000 lb truck
2. Find the mass of the above in kilograms.
3. If an object has reached terminal velocity, what
is the net force on the object? What’s its
acceleration?
4. T/F An object in orbit is actually falling.
Bell Work 4/4/11 – 5 minutes
START NEW MONDAY BELL RINGER
FOR 4TH QUARTER 
1. Define mass according to chemistry and
according to physics.
2. W5SAYW
Bell Work 3/30/12 – 5 min
1. Robbie can throw a 3.0 kg medicine ball with
an acceleration of 10.0 m/s2. What
acceleration could he give a 9.0 kg medicine
ball? Show your work!
2. If you were in a plane, would your weight or
mass change? Why?
The moon has a radius of 1.74 million meters and a mass of
7.32x1022 kg. In both MKS and FPS units, determine the
acceleration due to gravity on the lunar surface.
M = 7.32 x 1022 kg
r = 1,740,000 m = 1.74 x 106 m
a=?
a = GM
r2
a = (6.67 x 10-11)(7.32 x 1022 kg )
(1.74 x 106)2
48.824 x 1011 16.17 x 10-1
3.02 x 1012
1.62 m/s2
Bell Work 4/11/11 – 5 minutes
Mass (kg)
1.
1 kg
2.
50 kg
3.
0.102 kg
4.
_____ kg
5.
_____ kg
6.
_____ kg
7. W5SAYW
Weight on Earth
Newtons
Pounds
____N
____N
____N
500 N
50 N
____N
____lbs
____lbs
____lbs
____lbs
____lbs
2,000 lbs
Bell Work 3/29/12 – 5 min
1. A force of 250.0 lbs acts on an object with a
mass of 8.0 kg. What’s it’s acceleration?
2. What is gravity?
Bell Ringer 4/1/11 – 2 min
1. If the mass of an object magically
doubled, the force of gravity between it
and other objects __________.
2. If the distance between two objects
doubles, the force of gravity between
them is ____ what it was.
Bell Work 4/7/11 – 5 minutes
Use the conversions between lbs, kg, and N in your notes to
answer the following questions.
1. What is the difference between mass and
weight? Give 2 units that measure weight and
1 unit that measures mass.
2. Change the following weights to Newtons.
12 lb bowling ball
117 lb teen
1600 lb car
3. Find the weight of the following masses in
Newtons AND pounds.
1 kg
5 kg
1000 kg
If Pandora has a mass of 5.00 x 1024 kg and a radius of
6.00 x 103 km, find the weight of a 110 kg Na’vi on Pandora’s
surface. (Pay attention to the units!)
MP = 5.00 x 1024 kg
mN = 110 kg
r = 6.00 x 103 km = 6.00 x 106 m
W = Fg =?
Fg = GMPm
r2
Fg = (6.67 x 10-11)(5.00 x 1024 kg )(110 kg)
(6.00 x 106)2
Fg = 1019 N
Tips for using the G equation.
• Make sure you square r!
• You’ll be dealing with big numbers…don’t
forget the exponents! “x 10-11”!
• Double check your answers.
Satellite Motion
1. What is a satellite?
2. What are the forces acting on a satellite?
3. How long does it take a satellite to orbit
Earth?
4. Can we see them with the naked eye?
5. How fast do you have to travel to get
escape this planet?
14.2 Circular Orbits
The speeds of the bowling ball and the satellite are
not affected by the force of gravity because there is
no horizontal component of gravitational force.
14.2 Circular Orbits
The satellite is always moving at a right angle (perpendicular)
to the force of gravity.
• It doesn’t move in the direction of gravity, which would
increase its speed.
• It doesn’t move in a direction against gravity, which
would decrease its speed.
• No change in speed occurs—only a change in direction.
14.4 Energy Conservation and Satellite Motion
For a satellite in circular orbit, no force acts along the
direction of motion. The speed, and thus the KE,
cannot change.
What force or forces hold satellites in orbit?
14.2 Circular Orbits
A satellite in circular orbit close to Earth moves
tangentially at 8 km/s (5 mi/s). During each second, it
falls 5 m beneath each successive 8-km tangent.
What happens to the velocity of a satellite as the
distance from Earth increases?