What is Gravity?
-
Upload
james-patton -
Category
Documents
-
view
44 -
download
1
description
Transcript of What is Gravity?
What is Gravity?
• Write down anything you may know about gravity.
• Any examples of gravity
• Where you may find it or not find it!
What is Gravity?Gravity is an attraction that acts between any two objects that have a mass.So why isn’t your notebook attracted to you now?1. Gravity is only significant if, one or both of the objects are very massive (like a planet, star, or moon).Scientist’s know the acceleration of gravity is…
= 9.8m/s2
Let’s review…What’s matter?Anything that has a mass and takes up
spaceSo…What’s mass?How much matter is in an object.Then what’s Weight?How much gravity is pulling on an object.
An example of GravityEvery object applies a gravitational force to every other object.
So why does an apple fall from a tree?
The apple falls because it is more attracted (gravitational force) to the Earth than it is to the tree.
Differences Between Gravity and Friction
1. The force of gravity acts even when objects are not touching.2. Friction must ALWAYS be touching!3. The force of friction can never make an object speed up!4. Friction always points in the opposite direction of motion, 5. But gravity sometimes points in the direction of motion.
Mass and Distance
Mass and Distance affect Gravitational Force.The force of gravity depends on the masses of two objects and the distance between them.2. The greater the mass of an object, the more gravity it has pulling on it and other objects.
More about Gravity3. The further away the object is from the center of the Earth, the less gravity it will have pulling on it.
The Acceleration Due to Gravity:How does g change with altitude?
Altitude (m)
Distance From the Center of
g due to the Earth's
Gravity What has This
Altitude?the Earth
(m) (m/s2)0 6378100 9.799823 Lying on the Earth 2 6378102 9.799817 Height of a person4 6378104 9.799811 On a small roof
137 6378237 9.799402 Highest point in Delaware381 6378481 9.798652 Empire State Building
8848 6386948 9.772690 Height of Mount Everest12000 6390100 9.763051 Airplane
340000 6718100 8.832994 International Space Station6378100 12756200 2.449956 Twice the Earth's Radius
378024900 384403000 0.002698 The Moon
Does the gravitational pull near the surface change much?
No! The gravitational pull remains nearly constant! You would have to be hundred’s of miles away for gravity to really affect you!
Summarizing Gravity1. Gravity is only significant if, one or
both of the objects are very massive (like a planet, star, or moon).
2. As object get larger, the more gravity is pulling on them.
3. As objects get further away from each other, the less gravity is pulling on them.
Earth vs. Terrestrial Planets (Rocks)
Earth vs. Jovial Planets (Gas)
Sun vs. The Planets
Sun vs. Other Stars
Other Stars
More about Gravity Gravity is the reason why weight and
mass are two different measurements!!!
Mass is related to the amount of matter in an object.
Weight = the force of gravity pulling on any object. (w=mg)
So…which one would change if you were on the moon? Why?
Weight, because the force of gravity pulling on an object on the moon is only 1/6 of that on the Earth!
Gravity DropIf I drop a golf ball and a plastic fuzzy ball at the same time, which one hits the table first?The both hit at the same time!
BUT, what if I drop a volley ball and a bowling ball at the same time? Which one will hit the ground first?Let’s try it!So what happened?
Gravitational Force Formula My name is
Sir Isaac Newton and I figured this
out!
d is the distance between the centers ofthe two objects.
G is called the “gravitation constant” it equals (6.67x10-11 N x m2/kg2)and makesthe units right! Units for g =
221
G distance
massmassGF
Newton’s (N)
The Acceleration Due to Gravity:
So what is g for the moon, on the surface of the moon?
2moon
moonmoon
d
mGg
2
222211
moonm 1737100
kg 107.3477/kgmN106.673g
2moon m/s 1.62g
QUESTION????Which has more gravitational force…the earth and you or you and your neighbor?Why? (Use the formula… FG = G x m1 x m2
d2
You (60.4 kg) and your neighbor (70.5 kg) and d=1.5 m
You (60.4 kg) and the earth (5.9742×1024 kg)
But what is your weight?
2
2211
G1.5m
kg 60.4kg 70.5/kgmN106.673F
2
242211
Gm 6378100
kg 60.4kg 105.97kgmN106.673F
/
2m/s 9.8kg 60.4gmwThey’re the same!
… but how?!?!?!
1.26 x 10 -7 N
591 N
591 N
The Acceleration Due to Gravity:
We can calculate it! At ground level:
2
242211
Gm 6378100
kg 60.4kg 105.97/kgmN106.673F
What’s this? 9.80 m/s2 = g
2dmG
g
But we can calculate “g” anywhere, caused by any object with mass!
RFA 18 #4D (6.673x10-11Nxm2/kg2) (61kg) (63kg) (4m)
U kg, m, N x m2/kg2
F FG = G x m1 x m2 d2
A FG= (6.673x10-11Nxm2/kg2) (61kg) (63kg)(4m)2
S FG = 1.60 x 10-8 N
Gravity Practice Problems
Use DUFASRemember G=6.673x10-11Nxm2/kg2
1) m1 = 15 kg
m2 = 996 kg
d = 596 m
3) m1 = 600 kg
m2 = 72,684 kg
d = 30 m
2) m1 = 232 kg
m2 = 9,456 kg
d = 56 m
4) m1 = 7.35x1022 kg
m2 = 5.97x1025 kg
d = 3.84x108 m
1. D U F A
m1 = 15 kg
m2 = 996 kg
d = 596 m G=6.67x10-11N
Kg, m
N x m2/kg2
S
221
G dmmG
F
221
G dmmG
F
N102.80Fm 355216
mN109.97F
m 596
kg 996kg 15/kgmN106.673F
12G
2
27
G
2
2211
G
2. D U F A
m1=
232kg
m2=
9,456 kg
d = 56 m G=6.67x10-11N
Kg, m
N x m2/kg2
S
221
G dmmG
F
221
G dmmG
F
N104.66Fm 3136
mN101.46F
m 56
kg 9456kg 232/kgmN106.673F
8G
2
24
G
2
2211
G
3. D U F A
m1 =
600 kg
m2 =
72,684 kg
d = 30 mG=6.67x10-11N
Kg, m
N x m2/kg2
S
221
G dmmG
F
221
G dmmG
F
N103.23Fm 900
mN102.91F
m 30
kg 72684kg 600/kgmN106.673F
6G
2
23
G
2
2211
G
4. D U F A
m1=
7.351022 kg
m2 =
5.971025 kg
d =
3.84108 m
G=6.67x10-11N
Kg, m
N x m2/kg2
221
G dmmG
F
221
G dmmG
F
N101.98Fm 101.47mN103.84
F
m 103.84
kg 105.97kg 107.35/kgmN106.673F
21G
217
28
G
28
25222211
G
S
Gravity Practice ProblemsG= 6.673x 10-11 N x m2/kg2
In DUFAS
1. What is the gravitational attraction between an object with a mass of 10 kg and another object with a mass of 20 kg if they are separated by 0.01 meters?
Fg= 0.0001334 N 2. What is the gravitational attraction between my 10 kg killer Poodle and his 2kg bone that is 20m away from him?
Fg= 3.335 x 10-12 N
Gravity Practice1. Explain why a tree’s leaf falls to
the earth.
2. Who has more gravity pulling on them…a 350 lb offensive lineman or a 215 lb wide receiver on a football field? And why?
3. Why is there less gravity on the moon than here on Earth?
Gravity Answers1. The leaf falls to the Earth b/c the
Earth has a larger mass than the tree so it has a greater gravitational pull on the leaf.
2. The 350 lb lineman b/c he has more mass. More mass= more gravity pulling on that mass.
3. There is less gravity on the moon because you are very far from the center of the Earth so the gravitational pull is only 1/6th of Earth.