Transcript Act 7 Gravity

ACTIVITY #7: GRAVITY: THE INVISIBLE FORCE
Gravity is a force from which we can not escape its
effects. Right now you are being pulled downward
by the Earth’s gravity; it’s the force that we
commonly call our weight. But it may surprise you that you are
also being pulled by Mar’s gravity, Pluto’s gravity, and by many
other planets and stars outside of our solar system.
When we look at pictures of astronauts in space, they appear to
be floating around as if there were no gravity at all. The Apollo
space missions fascinated people around the world as they
watched the astronauts bounce and jump around the surface of
the Moon. With past and present missions in space,
gravity is a force that must be understood and
considered to allow for a safe and healthy space
mission. These observations of space raise a large
number of questions.
•What is gravity?
•Do astronauts in space really have no weight?
•What effect does space travel have on the human
body?
•How does gravity affect your life?
ACTIVITY OVERVIEW
The first part of the activity is the viewing of a video about gravity,
which serves as an overview for the entire activity. This leads into
several other investigations and demonstrations, each targeting a
specific variable that affects gravity.
MAIN IDEAS: In this lab activity, you will learn…………
 Masses of objects and the distance between them affects the
attractive force of gravity between them.
 Gravity is always present and can act without touching, hence
the reason that it is often called the “invisible force.”
gravity alone keeps the planets, and other objects, in our solar
system in orbit around the Sun and that is the Sun’s primarily
responsible in our solar system.
 Mass and weight represent two different quantities.
• The human body has adapted over time to life with gravity and
prolonged space travel affects the human body.
• Since each planet in our solar system has a different mass,
each has its own unique gravitational force on other objects.
The Sun is the gravitationally dominant object in our solar
system
• Gravity has an influence on observable phenomena such as
tides, planetary orbits and our own ability to move and function
on Earth
What is Gravity? Gravity is one of the four fundamental forces
in our universe. It is an attractive (pulling) force between objects,
and the objects can exert a gravity force on one another without
even touching. It is for this reason that gravity is sometimes called
the invisible force. The amount of force between the objects
depends on the masses of the objects and the distance between
them. If the mass increases, so does the force of gravity. If the
distance between the objects increases, the force of gravity
decreases; but the force of gravity never goes to zero.
All objects exert their force of gravity (we could even
calculate your own personal “gravity force” if we wished), but in
most cases, objects are too small to
really concern ourselves with their
affects. The force involves two objects
and will change size based upon the
characteristics of the second object.
This is not the case with large objects
such as planets, stars and asteroids.
What Newton discovered is that the force of gravity was universal
- it behaves the same way everywhere in the universe.
The Sun and the planets have a gravitational pull on each other,
but because the Sun is so much more massive, its gravity
dominates the solar system and is the reason why the planets
orbit the Sun, not the other way around. The Earth’s gravity is
responsible for keeping our Moon in orbit around our planet.
Other forces:
Strong force-holds nucleus
together
Electromagneticattraction,repel
Weakbeta(radioactive)decay
Gravity and Planets – Why are most space objects spherical?
On Earth, we typically say that gravity pulls
things straight downward, but the truth is that
gravity actually pulls toward the center of
the Earth. If you look at a globe, vertically
downward in Delaware is not the same
direction as vertically downward in Hawaii.
So, when talking about the force of gravity
on a global or astronomical scale, it would
be more accurate to say that gravity acts
inward, towards the Earth’s center. When our solar system was
forming, there were many small pieces of gas and dust, each
having their own very small amount of gravity. As these small
pieces started to stick together, the combined ( now larger and
more massive) object increased its gravity and pulled more and
more pieces together from all directions. This caused the
formation of objects in a spherical shape.
So How Do Astronauts Float Around in Space?
We have all seen the images of astronauts floating around in
space and it is referred to as a “weightless” or “microgravity”. But
this contradicts our previous discussion that gravity never goes to
zero. The terms weightlessness, zero gravity, and microgravity
refer to a sensation of being weightless. By all appearances,
gravity has disappeared, but this is not true. The space shuttle,
the space station,
and satellites are actually falling towards
the Earth because the Earth’s gravity is
pulling them downward just like it would do
to any object that get tossed up into the air.
The spacecraft and astronauts are moving
forward while they are also falling
downward. Since the Earth is a sphere, the
astronauts and the spacecraft actually fall
around the Earth.
You would feel the same sensation, for a short amount of time if
you were to ride the Free Fall ride at Six Flags Great Adventure in
New Jersey or if you rode in the Vomit Comet, which is
an aircraft that is used to train astronauts for this free fall condition
Due to this free fall situation, it appears as if all objects have no
weight, when actually they have not traveled
have not traveled far enough away from the center of the
Earth to experience any significant weight loss. What is really
happening is that all of the objects are falling at the same rate
around the Earth. Since things in this free fall environment
behave like there is no gravity at all, scientists use the terms
weightlessness, zero gravity, and microgravity to describe it even
though the gravity is not zero or “micro”.
How Do Humans React to Space?Humans may live in space for
longer periods of time in the future. Past missions in space travel
have revealed that this free fall (or microgravity) environment can
have negative effects on the human body. Our bodies have
evolved to handle the Earth’s always-present downward force of
gravity, but when put into a situation, such as in orbit, where the
body feels as if the force of gravity was turned off, the human
body adapts to the new environment. This is the reason that
astronauts must exercise regularly in space. As scientists study
ways to combat gravity related problems in space, such as bone
degeneration, they have also made advances in similar problems
already existing on our planet.
Part A: Video, Gravity: The Invisible Force
After viewing
video
T/F
1.Our body structure would be the same if we grew up in zero gravity.
F
2. The rings of Saturn are moons that were ripped apart by gravity.
T
3. Gravity helps in allowing life to exist on planet Earth.
T
4. It takes 2 days to reach outer space in the space shuttle.
F
5. We have muscles to pick things up because of gravity.
T
6. The height of mountains is affected by gravity.
T
7. Human life is very different in the absence of gravity.
T
8. Humans get weak in space, but feel strong.
T
9. Astronauts get stronger muscles when they go into space.
F
10. Bones become stronger in space.
F
Part 2: Video Discussion Questions
1.
Give one example of how the human body has evolved
because of gravity. Bones, muscles and blood pressure are all
designed to defeat gravity. We can keep our feet on the ground
because of gravity.
2. What effect did gravity have on Saturn? The enormous
gravitational pull ripped apart nearby moons, therefore forming the
rings. The gravity of Saturn was so strong that it prevented moons
from forming, and so we have rings.
3. How does gravity contribute to life on Earth? Gravity
contributes to the success of living organisms because of its
ability to hold the atmosphere and water in place on our planet.
4. Give one example of how humans defy gravity. We can hold
our heads up, by using our neck muscles as we walk. Our heart
pumps blood upwards and our muscles support our body. Our
vestibular organ allows us to balance ourselves and stop from
falling over.
5. Give an example of something gravity allows you to do? We
can shape ourselves with exercise using weights. Roller coasters
move downward at a very fast rate and we feel a brief “weightless”
moment (exactly the same experience that astronauts feel in
orbit). Any other examples.
6. How does an astronaut’s perception of the space around him
change in the free fall/microgravity environment of space? It is
very hard to tell up from down. Astronauts are able to lift very
heavy objects. It is very difficult to walk (we float).
7. What happens to an astronaut’s organs when they are in
space? The heart, diaphragm and liver move as ligaments relax.
The face becomes puffy as fluids move into the head and tissue.
8. What happens to an astronaut’s bones when they are in space?
Bones demineralize and become brittle in space which could lead
to bone fractures.
9. What happens to an astronaut’s muscles when they are in
space over a period of time? Muscles atrophy and get weaker in
space. (It could be easily related a student who had a leg or arm
in a cast for several weeks and then feels that they muscles are
weaker by their non-use during that period)
PART B: How much would you weigh at different locations
in our Solar System?
How much you weigh depends on the force of gravity at your
location. The table shows what the force of gravity would be at
different locations in our solar system based on a value of 1 on
the Earth’s surface. For example, if you weighed 100 pounds on
Earth, you would weigh 17 pounds on the Moon. 100 pounds
(your Earth weight) multiplied by 0.17 (the gravity factor for the
moon) = 17 pounds. This is about 1/6 the gravity on Earth.
Remember, your mass does not change at different locations.
Your mass remains the same; it is your weight that changes due
to the force of gravity on the different planets.
Question: Put your list of locations in order from where you weigh
the most to where you weigh the least. After looking at this data,
what do you think causes the variation in your weight?
PART C: How does the Mass of a Planet
affect Jump height?
Problem:
How does the Mass of a Planet affect
how high you can jump?
Independent Variable:
Dependent Variable:
Hypothesis:
Materials: Meter Stick Calculator
Procedure:
•Working in groups of three, have one member of the group hold a
meter stick vertical to the ground with the zero end touching the
ground.The second group member will observe and record the
jump height of group member three. Group member three makes
a standing jump next to the meter stick. This height is recorded for
three jumps. Average the three jumps together and record the
average jump height on Earth.
•Reverse roles two more times so that each member of the group
is able to be the jumper and get their average jump height on
Earth. Calculate average jump height on Earth
JUMP
TRIAL 1
TRIAL 2
TRIAL 3
HEIGHT
41
42
42
AVERAGE
JUMP
42
1. Using Table 2, calculate your average jump height at
other locations in the solar system. Example to
follow.
2. Complete Table 3 by listing the planets, Sun and
dwarf planet Pluto and the height of your jump from
the planet with the least mass to the planet with the
greatest mass. Example to follow.
3. Create a graph comparing the planets in increasing
order of mass to the jump height. Example to follow.
Table 2: How Jump height is determined by the Mass of the Solar System Object
Location
Mass of the
Solar System
object 1023 kg
Average Height
of Jump on
Earth (cm)
Conversion for
the Height of
Jump
Jump Height
on the location
(cm)
Mercury
3.3
42 (cm)
X 2.65
111.3 (cm)
Venus
48.7
42
X 1.10
46.2
Earth
59.8
42
X1
42
Mars
6.42
42
X 2.64
110.9
Jupiter
19000
42
X .039
16.38
Saturn
5690
42
X 0.94
39.5
Uranus
868
42
X 1.10
46.2
Neptune
1020
42
X 0.88
36.9
Dwarf
Planet
Pluto
Sun
0.129
42
X 13.2
554.4
19,900,000
42
X 0.04
1.68
Solar System Object
Height of Jump
1. Dwarf Planet Pluto
554.4 cm
2 .Mercury
111.3
3. Mars
110.9
4. Venus
46.2
5. Earth
42
6. Uranus
46.2
7. Neptune
36.9
8. Saturn
39.5
9. Jupiter
16.38
10. Sun
1.68
120
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Jump height in cm
Jump height on planets from planets least
to most massive
Planets least to most massive
Using the data from the above tables, create a bar graph comparing the
mass of the planets and dwarf planet to the height of your jump. Use
the list of planets and dwarf planet Pluto to organize the planets on the
x axis from least to greatest mass.
Answer the following questions using your data
1. What relationship do you see with the mass of the object and
Jump Height?
As the mass of the planet increases, the jump height decreases.
2. What does the mass of the planet have to do with gravity? Why
does this influence the Jump Height?
The greater the mass of the planet, the stronger the gravitational
pull. The greater the mass of the planet, the lower the jump height
will be because the gravitational pull in greater on more massive
planets.
Part D: Modeling Gravity’s Effects on Planets
Demonstration 1
QUESTIONS:
What keeps the Earth from traveling outside of our Solar System?
What makes it revolve around the Sun and not just move further into outer
space?
1. Get to in pairs and hold hands. You
should spin around together in a circle. You
should feel the force on your arms that is between you
your partner, causing both of you to move in a circular
pattern.
2. What do you think would happen if you were
to let go. This is a topic we addressed in 6th grade Force and Motion, where it is
emphasized that a force is needed to cause an object to move in a circle. It is
not natural for any object to move in a circle-a force must be present for this to
happen. In this demonstration, the pulling force of your arms represents gravity
(Gravity is a pulling force ) and that one person would represent a planet while
the other person represents
the Sun. This model also serves the purpose of showing that a gravity force is
exerted by both objects on each other.
Demonstration 2
For this demonstration, we will use a lightweight ball tied to the
end of a string to model the situation again, but with this
demonstration, students can actually test out what would happen
if they let go of the string.
Use the string and ball supplied and swing
the ball around in an arc over your head. To
demonstrate that there is a force on the
string, let go. We have selected a ball which
will not injure anyone whom it might hit.
Questions: What force caused the ball to move
in a circle?
What happened when the force was no
longer present?
What would happen if the Sun’s gravity
were to suddenly turn off?
Distance and its Influence on Gravity
Table 1: Average Orbital Speed of the Planets in Our Solar System
Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Dwarf Planet Pluto
Average Orbital Speed (km/sec)
48
35
30
24
13
9.7
6.8
5.4
4.7
Table 2: Planet Distance from the Sun
Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Dwarf Planet Pluto
Distance from Sun in AU
0.39
0.72
1.0
1.52
5.20
9.58
19.20
30.05
39.24
Graphs: The Influence of Distance on Gravity
45
40
35
30
25
20
15
10
5
0
Dwarf Planet
Neptune
Uranus
Saturn
Jupiter
Mars
Earth
Venus
Distance from Sun in
AU
Mercury
Distance from sun in AU
Distance from Sun in AU
Planet
60
50
40
30
20
10
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Average Orbital
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Orbital speed in km/sec
Average Orbital Speed (km/sec)
Planet
The astronomical unit
(AU or au or a.u.) is a
unit of length. It is
approximately equal to
the mean distance
between Earth and Sun.
The currently accepted
value of the AU is
about 150 million
kilometers or 93 million
miles.
Discussion Questions:
1.
Using the graphs above, do you see any
correlation between the distance of the planet from
the Sun and the influence of gravity on its orbital
speed?
The orbital speed is the average speed the
planet is moving as it revolves around the Sun one
time. Explain how gravity and distance would
influence this speed.
2.
Name and describe two factors that influence
gravitational pull of a planet.
Investigating Further…
When planning future long term missions in space, many health
factors must be addressed. Due to the effects of microgravity on
the human body, many health problems have occurred that must
be addressed in future long term space missions. Microgravity
means that there is a very small amount of gravity present in
space. After extended periods of time in space, bone disorders,
cardiac problems, sleep disorders, radiation effects, immune
disorders, muscle changes, inner ear and balance issues and
psychological factors have surfaced. The National Space and
Biomedical Research Institute is actively researching the effects
of microgravity on the human body and looking for ways to
counteract these harmful effects. Search the internet for a more
complete description of harmful effects of long duration space
flights. The NSBRI web site is a great site to start. The site is as
follows: www.nsbri.org
Copy and Answer the following questions. Use your data to
support your responses.
 What is gravity?
 How does microgravity affect the human body?
 What does gravity allow us to do on Earth?
 What keeps the Earth and Moon in orbit?
 What is the difference between
your weight and mass?
 What two factors influence
gravity?
 Why is gravity called the
invisible force?
Applying what you have learned …
1. In future long term missions to Mars, what gravitational influences
(related to travel and health), will mankind need to address?
2. If a human was born in space, why would they have difficulty if they
returned to Earth?
3. Why do astronauts feel like “superman” when they are in space?
4. How do these activities explain how gravity keeps the solar system
held together?
5. Use what you have learned to explain how games such as football,
basketball, gymnastics, hurdles or other sporting events would be very
different on other planetary bodies.