act 7 gravity

7/28/2019 Act 7 Gravity

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ACTIVITY #7: GRAVITY: THE INVISIBLE FORCE

Gravity is a force from which we can not escape its

effects. Right now you are being pulled downwardby the Earths gravity; its the force that wecommonly call our weight. But it may surprise you that you arealso being pulled by Mars gravity, Plutos gravity, and by many

other planets and stars outside of our solar system.

When we look at pictures of astronauts in space, they appear tobe floating around as if there were no gravity at all. The Apollospace missions fascinated people around the world as they

watched the astronauts bounce and jump around the surface ofthe Moon. With past and present missions in space,gravity is a force that must be understood andconsidered to allow for a safe and healthy spacemission. These observations of space raise a large

number of questions.


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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 intoseveral other investigations and demonstrations, each targeting aspecific variable that affects gravity.


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Masses of objects and the distance between them affects theattractive force of gravity between them.

Gravity is always present and can act without touching, hencethe reason that it is often called the invisible force.

gravity alone keeps the planets, and other objects, in our solarsystem in orbit around the Sun and that is the Suns primarily

responsible in our solar system.

Mass and weight represent two different quantities.

The human body has adapted over time to life with gravity andprolonged 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 solarsystem

Gravity has an influence on observable phenomena such as

tides, planetary orbits and our own ability to move and functionon Earth

MAIN IDEAS: In this lab activity, you will learn


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What is Gravity? Gravity is one of the four fundamental forcesin our universe. It is an attractive (pulling) force between objects,and the objects can exert a gravity force on one another withouteven touching. It is for this reason that gravity is sometimes called

the invisible force. The amount of force between the objectsdepends on the masses of the objects and the distance betweenthem. If the mass increases, so does the force of gravity. If thedistance 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 toreally concern ourselves with theiraffects. The force involves two objectsand will change size based upon thecharacteristics of the second object.This is not the case with large objects

such as planets, stars and asteroids.


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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 planetsorbit the Sun, not the other way around. The Earths gravity is

responsible for keeping our Moon in orbit around our planet.

Other forces:

Strong force-holds nucleus

together

Electromagnetic-

attraction,repel

Weak-

beta(radioactive)decay


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Gravity and Planets Why are most space objects spherical?

On Earth, we typically say that gravity pullsthings straight downward, but the truth is that

gravity actually pulls toward the center ofthe Earth. If you look at a globe, verticallydownward in Delaware is not the samedirection as vertically downward in Hawaii.So, when talking about the force of gravity

on a global or astronomical scale, it wouldbe more accurate to say that gravity actsinward, towards the Earths center. When our solar system wasforming, there were many small pieces of gas and dust, each

having their own very small amount of gravity. As these smallpieces started to stick together, the combined ( now larger andmore massive) object increased its gravity and pulled more andmore pieces together from all directions. This caused the

formation of objects in a spherical shape.
http://www.pipelinenews.org/readerimages/planet.gifhttp://www.pipelinenews.org/readerimages/planet.gif


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SoHow Do Astronauts Float Around in Space?

We have all seen the images of astronauts floating around inspace and it is referred to as a weightless or microgravity. But

this contradicts our previous discussion that gravity never goes tozero. The terms weightlessness, zero gravity, and microgravityrefer 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 towardsthe Earth because the Earths 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 movingforward while they are also fallingdownward. Since the Earth is a sphere, theastronauts and the spacecraft actually fall

around the Earth.


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You would feel the same sensation, for a short amount of time ifyou were to ride the Free Fallride at Six Flags Great Adventure inNew Jersey or if you rode in the Vomit Comet, which is

an aircraft that is used to train astronauts for this free fall conditionDue to this free fall situation, it appears as if all objects have noweight, when actually they have not traveledhave not traveled far enough away from the center of the

Earth to experience any significant weight loss. What is reallyhappening is that all of the objects are falling at the same ratearound the Earth. Since things in this free fall environmentbehave like there is no gravity at all, scientists use the termsweightlessness, zero gravity, and microgravityto describe it even

though the gravity is not zero or micro.


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How Do Humans React to Space?Humans may live in space forlonger periods of time in the future. Past missions in space travelhave revealed that this free fall (or microgravity) environment canhave negative effects on the human body. Our bodies have

evolved to handle the Earths always-present downward force ofgravity, but when put into a situation, such as in orbit, where thebody feels as if the force of gravity was turned off, the humanbody adapts to the new environment. This is the reason that

astronauts must exercise regularly in space. As scientists studyways to combat gravity related problems in space, such as bonedegeneration, they have also made advances in similar problemsalready existing on our planet.


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Part 2: Video Discussion Questions1. 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 groundbecause of gravity.

2. What effect did gravity have on Saturn? The enormousgravitational pull ripped apart nearby moons, therefore forming therings. 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? Gravitycontributes to the success of living organisms because of itsability to hold the atmosphere and water in place on our planet.

4. Give one example of how humans defy gravity. We can holdour heads up, by using our neck muscles as we walk. Our heartpumps blood upwards and our muscles support our body. Ourvestibular organ allows us to balance ourselves and stop from

falling over.


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5. Give an example of something gravity allows you to do? Wecan shape ourselves with exercise using weights. Roller coasters

move downward at a very fast rate and we feel a brief weightlessmoment (exactly the same experience that astronauts feel inorbit). Any other examples.

6. How does an astronauts perception of the space around him

change in the free fall/microgravity environment of space? It isvery hard to tell up from down. Astronauts are able to lift veryheavy objects. It is very difficult to walk (we float).

7. What happens to an astronauts 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.


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8. What happens to an astronauts bones when they are in space?

Bones demineralize and become brittle in space which could leadto bone fractures.

9. What happens to an astronauts muscles when they are inspace over a period of time? Muscles atrophy and get weaker inspace. (It could be easily related a student who had a leg or armin a cast for several weeks and then feels that they muscles are

weaker by their non-use during that period)


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PART B: How much would you weigh at different locationsin 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 atdifferent locations in our solar system based on a value of 1 onthe Earths 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 themoon) = 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 dueto the force of gravity on the different planets.

Question: Put your list of locations in order from where you weighthe most to where you weigh the least. After looking at this data,what do you think causes the variation in your weight?


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PART C: How does the Mass of a Planetaffect Jump height?

Problem:How does the Mass of a Planet affect

how high you can jump?

Independent Variable:

Dependent Variable:Hypothesis:


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Materials: Meter Stick CalculatorProcedure:

Working in groups of three, have one member of the group hold a

meter stick vertical to the ground with the zero end touching theground.The second group member will observe and record thejump height of group member three. Group member three makesa standing jump next to the meter stick. This height is recorded forthree 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 groupis able to be the jumper and get their average jump height onEarth. Calculate average jump height on Earth

JUMP TRIAL 1 TRIAL 2 TRIAL 3 AVERAGEJUMP

HEIGHT 41 42 42 42


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1. Using Table 2, calculate your average jump height at

other locations in the solar system. Example tofollow.

2. Complete Table 3 by listing the planets, Sun anddwarf planet Pluto and the height of your jump from

the planet with the least mass to the planet with thegreatest mass. Example to follow.

3. Create a graph comparing the planets in increasingorder of mass to the jump height. Example to follow.

T bl 2 H J h i h i d i d b h M f h S l S Obj


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Table 2: How Jump height is determined by the Mass of the Solar System Object

Location Mass of theSolar Systemobject 1023 kg

Average Heightof Jump onEarth (cm)

Conversion forthe Height ofJump

Jump Heighton 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 X 1 42

Mars 6.42 42 X 2.64 110.9Jupiter 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

DwarfPlanetPluto

0.129 42 X 13.2 554.4

Sun 19,900,000 42 X 0.04 1.68

S l S t Obj t H i ht f J


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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


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Jump height on planets from planets least

to most massive

0

20

40

60

80

100

120

2.M

ercury 3.Mars

4.Venus

5.Earth

6.Uranus

7.Nep

tune8.

Saturn

9.Ju

piter

10.Sun

Planets least to most massive

Jumpheightincm

Using the data from the above tables, create a bar graph comparing themass of the planets and dwarf planet to the height of your jump. Usethe list of planets and dwarf planet Pluto to organize the planets on thex axis from least to greatest mass.


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Answer the following questions using your data

1. What relationship do you see with the mass of the object andJump 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? Whydoes this influence the Jump Height?

The greater the mass of the planet, the stronger the gravitationalpull. The greater the mass of the planet, the lower the jump heightwill be because the gravitational pull in greater on more massive

planets.

P t D M d li G it Eff t Pl t


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Part D: Modeling Gravitys Effects on Planets

Demonstration 1QUESTIONS: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. Youshould 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 circularpattern.

2. What do you think would happen if you wereto let go. This is a topic we addressed in 6th grade Force and Motion, where it isemphasized that a force is needed to cause an object to move in a circle. It isnot natural for any object to move in a circle-a force must be present for this tohappen. In this demonstration, the pulling force of your arms represents gravity(Gravity is a pulling force ) and that one person would represent a planet whilethe other person representsthe Sun. This model also serves the purpose of showing that a gravity force isexerted by both objects on each other.

D t ti 2


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Demonstration 2

Use the string and ball supplied and swingthe 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 whichwill not injure anyone whom it might hit.

Questions: What force caused the ball to movein a circle?

What happened when the force was nolonger present?

What would happen if the Suns gravity

were to suddenl turn off?

For this demonstration, we will use a lightweight ball tied to theend of a string to model the situation again, but with this

demonstration, students can actually test out what would happenif they let go of the string.

Di t d it I fl G it


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Distance and its Influence on GravityTable 1: Average Orbital Speed of the Planets in Our Solar System

Planet Average Orbital Speed (km/sec)

Mercury 48

Venus 35

Earth 30

Mars 24

Jupiter 13

Saturn 9.7

Uranus 6.8

Neptune 5.4

Dwarf Planet Pluto 4.7

Table 2: Planet Distance from the Sun

Planet Distance from Sun in AU

Mercury 0.39

Venus 0.72

Earth 1.0

Mars 1.52

Jupiter 5.20

Saturn 9.58

Uranus 19.20

Neptune 30.05

Dwarf Planet Pluto 39.24

G h Th I fl f Di t G it


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Average Orbital Speed (km/sec)

0

10

20

30

40

50

60

Mercu

ry

Venu

sEa

rthM

ars

Jupit

er

Satu

rn

Uran

us

Neptun

e

DwarfP

lanetPl

uto

Planet

Orbitalspe

edinkm/sec

Average Orbital

Speed (km/sec)

Distance from Sun in AU

05

1015202530354045

Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

DwarfPlanet

Planet

DistancefromsuninAU

Distance from Sun inAU

Graphs: The Influence of Distance on Gravity

Theastronomical unit

(AU orau ora.u.) is a

unit of length. It is

approximately equal to

the mean distancebetween Earth and Sun.

The currently accepted

value of the AU is

about 150 millionkilometers or 93 million

miles.


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Discussion Questions:1. Using the graphs above, do you see any

correlation between the distance of the planet fromthe Sun and the influence of gravity on its orbitalspeed?

The orbital speed is the average speed the

planet is moving as it revolves around the Sun onetime. Explain how gravity and distance wouldinfluence this speed.

2. Name and describe two factors that influencegravitational pull of a planet.


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C d A th f ll i ti U d t t


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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 betweenyour weight and mass?

What two factors influence

gravity?

Why is gravity called theinvisible force?


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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 theyreturned 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 systemheld together?

5. Use what you have learned to explain how games such as football,basketball, gymnastics, hurdles or other sporting events would be verydifferent on other planetary bodies.

act 7 gravity

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