Transcript DV_The-Physics-of-Toys

The Physics of Toys (and Space)
Addendum to curriculum
for Ms. Decker’s 2nd Grade Class
Jamestown Elementary
By Darren McKnight
Spring 2001
1. Force
and
Friction
2. Energy
and
Machines
1
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?
2
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 an object cancel out
3
Forces
The man is standing still.
Are there any forces
on the man?
If so, draw them.
floor
4
Forces
The force due to gravity
is pushing him down.
Is there another
force?
Gravity
5
Forces
The other force is
the floor pushing back!
Which force is
greater?
Gravity
Floor
6
Forces
The force due to gravity
is the same in size,
but opposite in
direction, to the force
by the floor!!!!
Gravity
Floor
7
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?
8
Gravitational Force - Answer
• So what causes a gravitational force?
– Two objects are attracted to each other
Object 1 (has mass)
F1
F1 = F2
F2
Object 2 (has mass)
9
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
10
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?
11
Gravitational Force Answers
• Is there a gravitational force on the moon?
– Is it larger or smaller than the gravitational
force on the Earth?
• The gravitational force is smaller on the moon.
– Why?
• The moon is smaller (less massive) than the Earth.
12
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?
13
Final Force Example
Ms. Decker at the Pool
.
- What forces are acting on
Ms. Decker as she stands
on the end of the diving
board?
- Draw them.
14
Final Force Example
Ms. Decker at the Pool
.
- What forces are acting on
Ms. Decker as she stands
on the end of the diving
board?
Force from Ms. Decker (gravity)
Force from diving
board
15
Final Force Example
Ms. Decker at the Pool
.
- Which force is greater?
Force from Ms. Decker (gravity)
Force from diving
board
16
Final Force Example
Ms. Decker at the Pool
.
-Which force is greater?
They are equal since
Ms. Decker is not moving
Force from Ms. Decker (gravity)
Force from diving
board
17
Final Force Example
Ms. Decker at the Pool
.
-What if Ms. Decker walks off the
end of the diving board?
- Why?
18
Final Force Example
Ms. Decker at the Pool
.
-What if Ms. Decker walks off the
end of the diving board?
She starts to fall toward the water
- Why?
Gravity is still forcing down but there
is no force from the diving board
- Draw the forces on Ms. Decker.
19
Final Force Example
Ms. Decker at the Pool
-Draw the forces on Ms. Decker.
Gravity
-Why does Ms. Decker continue to fall?
.
Air Resistance
20
Final Force Example
Ms. Decker at the Pool
-Why does Ms. Decker continue to fall?
The force due to gravity is greater than
air resistance force opposing her fall.
Gravity
.
- What happens when Ms. Decker hits
the water.
Air Resistance
21
Final Force Example
Ms. Decker at the Pool
-What happens when she hits the water?
She gets wet!!!
.
22
Friction – Key Points
• What is friction?
• What makes friction greater?
• What makes friction less?
23
Friction
• Rubbing – create heat or slow down motion
or both
– What are examples of friction?
24
Friction
• Rubbing” – create heat or slow down motion or
both
– What are examples of friction?
•
•
•
•
Rubbing hands together to get warm
Putting sand on the road to prevent cars from sliding
Newspaper sliding across the driveway
Any more?
25
Friction
• Two items determine the friction force
– YES, FRICTION CREATES A FORCE!!!
• 1. Goes against the motion
• 2. Greater if surfaces are rough ; less is surfaces are smooth
• If we slid a book across the two surfaces below,
on which one would the book go farther?
A
B
26
Friction
• If we slid a book across the two surfaces
below, on which one would the book go
farther?
A
• Draw the forces on book.
A
B
27
Friction
• Draw the forces on book.
Book (gravity)
Friction
A
Table
28
Friction in Space
• Is there any friction in space?
• Is there any friction when objects come
back from space?
29
Friction in Space
• Is there any friction in space?
– No, no air or surfaces to slide against
• Is there any friction when objects come back from
space?
– Yes, the air creates a surface and a tremendous amount
of heat when objects comes back to Earth.
– Manned spacecraft have special heat shields so that
they do not burn up!!!!!!!
– Shooting stars are just cosmic “pebbles” burning up as
they come into the Earth’s atmosphere
30
Reentering Space Vehicle
31
Friction – Key Points
• What is friction?
– A force that opposes motion
• What makes friction greater?
– Rougher surface
• What makes friction less?
– Smoother surface
32
Friction – Final Example
Draw the forces on the picture. Hint: The puck is slowing down
as it moves across the table.
How could you increase the distance the puck would slide?
The puck is sliding this way…
33
Friction – Final Example
Draw the forces on the picture. Hint: The puck is slowing down
as it moves across the table.
How could you increase the distance the puck would slide?
Polish the table or polish the bottom of the puck – reduce friction!!!!
Force due to gravity
The puck is sliding this way…
Friction
Force from table
34
Friction Lab
• We will slide three pucks at the same speed
and measure how far they go
• We will plot the data and make observations
• Why might different pucks go different
pucks go different distances?
35
Friction Lab
• Why might different pucks go different
distances?
– The bottom surfaces might be smoother or rougher than
the others
• Everyone will record all of the data
– I will call off distance traveled and puck letter (A, B, or
C)
• Who wants to volunteer to slide the puck?
36
Friction Lab Data
18ft
15ft
X
12ft
9ft
X
X
X
A
B
Puck
6ft
3ft
C
For example, the plot above shows puck A going 10ft and 15ft
while puck B went 6 ft and 9ft
37
Friction Lab Data
18ft
15ft
12ft
9ft
6ft
3ft
A
B
C
Puck
Which puck traveled the farthest?________
What does that mean?___________________________
Which puck had the most friction?_________
38
Big Word of the Day
• A surface that is very rough means it has a
high coefficient of friction!
• Very impressive word to use at home!
– “Gee Mom, our tires have a very high
coefficient of friction!”
– “Hey Dad, that icy road has a very low
coefficient of friction!”
39
The Physics of Toys (and Space)
Addendum to curriculum
for Ms. Decker’s 2nd Grade Class
Jamestown Elementary
By Darren McKnight
Spring 2001
1. Force
and
Friction
2. Energy
and
Machines
40
Potential and Kinetic Energy –
Key Facts
• Potential energy – “stored” energy
– How can we “store” energy?
• Kinetic energy – energy of movement
– How is potential energy converted into kinetic energy?
• What is work?
– Exert a force over a distance
41
Potential Energy
Does the ball
have any stored
energy here?
Does the ball
have any stored
energy here?
42
Potential Energy
Does the ball
have any stored
energy here?
Does the ball
have any stored
energy here?
NO
YES, we moved the ball
against gravity (did work)
43
Force Review
What forces are acting on the ball while we
hold it still above the floor?
Draw and label them.
44
Force Review
Force due to gravity
Which force is greater?
They are the same, that is why
the ball is not moving!!!
Force of the hand
45
Potential Energy
What happens when we let go
of the ball?
If the ball is to move show the
direction of the ball.
Label the forces on the ball!!!!
46
Potential/Kinetic Energy
Gravity
velocity
What happens when we let go
of the ball?
It starts to fall – has kinetic energy
If the ball is to move show the
direction of the ball.
Label the forces on the ball!!!!
Air
Gravity is larger force than
resistance
air resistance
47
Potential and Kinetic Energy –
Key Facts
• Potential energy – “stored” energy
– How can we “store” energy?
• Kinetic energy – energy of movement
– How is potential energy converted into kinetic energy?
• What is work?
– Exert a force over a distance
48
Swing Set and Energy
Does a swing have any kinetic
energy when it is sitting still
unused? How about potential
energy?
KE _____ PE _____
Does a swing have any kinetic
energy when it is pulled up?
How about potential energy?
KE _____
PE _______ 49
Swing Set and Energy
Does a swing have any kinetic
energy when it is sitting still
unused? How about potential
energy?
KE __no_ PE _some_
Does a swing have any kinetic
energy when it is pulled up?
How about potential energy?
KE __no_
50
PE __more___
Swing Set and Energy
What happens when you let
go of the swing to the kinetic
energy and potential energy?
KE _____ PE _____
As the swing gets to the
bottom again what is the
energy?
KE _____ PE _______
51
Swing Set and Energy
What happens when you let
go of the swing to the kinetic
energy and potential energy?
KE _starts_ PE _goes down_
As the swing gets to the
bottom again what is the
energy?
KE _maximum_ PE _minimum_
52
Swing Set – Exchanging Energy
• So as the swing oscillates (another big word
to use at home – means “go back and
forth”) it exchanges kinetic energy for
potential and back again
• Why does the swing always eventually
stop?
53
Swing Set – Exchanging Energy
• Why does the swing always eventually
stop?
– Friction from where the chain attaches to the
swing set
– Air resistance
54
Springs
• What are springs used for?
• Can you describe how a spring “stores”
energy?
• Can you describe how a spring releases
kinetic energy?
55
Spring as a “Worker”
Spring
PE
KE
Relaxed
None
None
Squeezed
Maximum
None
Released
Some
Some
None
Maximum
V
Back to Middle
V
56
Spring Lab
• You will observe
– 1. How potential energy is stored in a spring
(compress the spring) and
– 2. Then converted into kinetic energy (the
spring flies up with some velocity) and
– 3. Then converted back into potential energy
(jumping up a certain distance)
57
Spring Lab
• Step 1: Compress spring a certain amount
– A little (first mark)
– A lot (second mark)
– All the way (third mark)
• Step 2: Let the spring go!
• Step 3: Record how high up the
spring goes on the stick
– Stick is marked in one foot sections by color
Work in pairs and put answers on the empty table
58
Data Collection for Spring Lab
Press Down the Spring
A little
How High it Jumps
brown
A little
A little
A lot
pink
A lot
A lot
All the way
red
All the way
All the way
The table above shows three example experiments: when the spring was
pushed down a little it stayed in brown, for “a lot” it went to pink, and
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when compressed “all the way” it went all the way to the red.
Data Collection for Spring Lab
Press Down the Spring
How High it Jumps
A little
A little
A little
A lot
A lot
A lot
All the way
All the way
All the way
Explain what is happening in your own words:_________________
______________________________________________________
60
______________________________________________________
Observations from Spring Lab
• The more you compress the spring the
farther up it jumps
– Give it more potential energy (stored in the
spring) then it has a greater kinetic energy
(shoots up higher)
• What causes the spring to slow down and
eventually stop?
61
Observations from Spring Lab
• What causes the spring to slow down and
eventually stop?
– Gravity is acting down on the spring slowing it
down
– There is probably some friction between the
spring and the stick
62
Satellites in Orbit
• Satellite is an object that goes around and
around another object
– The moon is a satellite of the Earth
– The space shuttle is a satellite when it goes into
space
– The Earth is a satellite around the Sun
• A satellite in orbit is much like a swing!!!
63
Satellites in Orbit
A
B
At point A the satellite is closest to the Earth and at Point B it
is farthest from the Earth.
What does that mean about its potential energy at points A and B?
64
Satellites in Orbit
A
B
What does that mean about its potential energy at points A and B?
Lowest potential energy at A and highest at B
So what do you think is true about the kinetic energy at
points A and B?
65
Satellites in Orbit
A
B
So what do you think is true about the kinetic energy at
points A and B?
The kinetic energy is smallest at point B (slowest) and
largest point A (fastest)
66
Machines – Key Facts
• What is a machine?
• Name some examples?
67
Machines – Key Facts
• What is a machine?
– Something that uses energy to do useful activities
• Name some examples?
–
–
–
–
–
Levers
Wheels and axles
Pulleys
Inclined planes
Screws
68
Space Machines
• Momentum wheel – spin up a wheel
to keep an object oriented
• Rocket – burn fuel, send exhaust
out back so rocket moves forward
• Solar Panels – convert sunlight
into electricity
69
Space Machines - Rockets
70
Space Machines - Satellites
71
Space Machines - Satellites
Hubble Space Telescope
72
1
Releasing The Hubble
2
3
4
What kind of machine
picked up the Hubble
and put it into space?
73
Space Machines - Satellites
Hubble Space Telescope – broken into pieces
74
Space Machines on Moon or
Other Planets
Moon
Mars
75
Space Physics – Overall Example
•
•
•
•
Forces
Energy – Potential and Kinetic
Machines
Friction
76
Rocket on the Launch Pad
What forces are acting on the rocket?
Draw on the forces.
77
Rocket on the Launch Pad
What forces are acting on the rocket?
Force due to gravity
Force from the ground
gravity
Ground
78
Rocket on the Launch Pad
What will happen when the rocket starts?
Draw on the forces.
79
Rocket on the Launch Pad
Air
resistance
What will happen when the rocket starts?
Force from the rocket is bigger
than the force due to gravity
and the air resistance
gravity
rocket
80
Releasing the Satellite
• When the rocket gets into space how might
the satellite be pushed away from the
rocket?
– Hint: What lab did we do where we store
potential energy in a simple device that was
later turned into kinetic energy?
81
RIGHT!!!! Springs are Used
springs
Last rocket
The cover also needs to
be taken off… How?
Why do you think we needed
a cover?
82
Satellite Then Unfolds Using a
Small Motor
Now it continues to go
around and around the
Earth.
What do we call that?
83
Satellite in Orbit
Where the satellite is located right now, what can you say about
the kinetic and potential energy of the satellite?
___________________________________________________
84
Satellite Reenters
• Eventually the satellite comes back to Earth
– WHY?
85
Satellite Reenters
• Eventually the satellite comes back to Earth
– WHY?
• Air resistance from the atmosphere will slow it down
• Maybe a rocket was fired to bring it back to Earth
• What happens to the satellite as it
reenters?
86
Satellite Reenters
• What happens to the satellite as it
reenters?
– It heats up and slows down due to friction
• It might melt and burn up completely depending on
what it is made of….
• Now you know all about rocket,
satellites, and space physics!!!!!
87
Physics and Science are Very
Important – Explain what is
happening around you everyday!
88
Write your name here
Miss Decker’s Class
May 2001
89