what factors affect the gravitational force?
TRANSCRIPT
What Factors Affect the Gravitational Force?
What Did You Learn?
What is the relationship between F1 and F2?
They are equal in magnitude but opposite in direction.
These forces are a Newton’s Third Law Pair!
What Did You Learn?
What type of relationship is there between Fg and m1?
Proportional!
The gravitational force increases!
What happens as mass 1 increases?
What Did You Learn?
What type of relationship is there between Fg and m2?
Proportional!
The gravitational force increases!
What happens as mass 2 increases?
What Did You Learn?
What type of relationship is there between Fg and m1?
Power!
The gravitational force decreases!
What happens as distance increases?
What Did You Learn?
Does your equation look like this?
Fg = constant * r-2
Fg = constantr2
What does that mean?
Creating a Mathematical Model
Fg = constantr2
Fg = constant * m1
Fg = constant * m2
Fg =constant *m1m2
r2
Because we are talking about gravity, the constant is represented by the letter G!
Fg =Gm1m2
r2
What is G?A scientist named Cavendish was trying to figure
out the internal structure of the Earth.
Designed an experiment to determine the Earth’s mass.
G = 6.67 x 10-11 Nm2/kg2
What’s the Attraction?Gravity is known as the weakest of the fundamental forces.
Let’s see how strong it actually is on an everyday level!
What is the force of gravity between a loving couple 30 cm apart if one
has a mass of 60 kg and the other has a mass of 75 kg?
Fg =Gm1m2
r2
Fg = 3.3 x 10-6 N
If the dance floor is frictionless, how long would it take them to reach each other?
A Little Perspective
xf = 1/2at2 + vot+ xo
If they are in a frictionless environment, how long would it take for Minnie and Mickey assuming that Mickey
remains motionless.
xf = 1/2at2
a = Fg/m
Minnie: a = 3.3 x 10-6 N/60 kg
a = 5.5 x 10-8 m/s2
xf = 1/2at2
xf = 0.30 m
t = 3302 s = 55 min
0.30 m
a = Fnet/m
Falling Apples
Newton developed this mathematical relationship.
A falling apple is experiencing the same force as the moon orbiting the Earth!
Why are planets different?
Let’s say you have an apple in free fall on the Moon.
Fg = maag
Fg =Gmamm
Rm2
maag =Gmamm
Rm2
ag =Gmm
Rm2
mE = 5.96 x 1024 kg mE = 5.98 x 1024 kg
Comparing GravityJupiter is about 320 x more massive than Earth.
FgE =GmEmO
r2
Jupiter has a radius that is 11 x bigger than Earth.
How does the force of gravity on Jupiter compare to that of Earth?
FgJ =GmJmO
rJ2
Fg =G(320mE)mO
(11rE)2
Comparing Gravity
gJ = 25 m/s2
FgJ =G(320mE)mO
(11rE)2FgJ =
320GmEmO
121rE2
FgJ =GmEmO
rE2
320
121FgJ =
320
121FgE
FgJ = 2.6FgE
gJ = 2.6gE
The Gravitational FieldA vector field is a model that helps us understand
interactions that occur at a distance.
Play with the simulation! Only use blue objects and sensors. Make three observations on your group’s slide!
What Did You Learn??
Period 2 Period 6 Period 8
The Gravitational Field
The gravitational field is always directed toward the mass that creates it.
The gravitational field gets smaller as you move away from the mass that creates it.
The Gravitational Field
The gravitational field is the same strength at all points that are equidistant around a
spherical object
The Gravitational Field
When there are multiple objects, each one will create its own gravitational field. The total
field will be the sum of their individual fields.
The Gravitational FieldThe gravitational field at any point in space is defined as the
gravitational force felt by a tiny unit mass placed at that point.
g = Fg
mFg = GmM
r2
g = GMr2
Gravity will get very small with large distances, but is
never zero!
There is no place in the Universe where it is zero!
The Gravitational FieldThe gravitational field at any point in space is defined as the
gravitational force felt by a tiny unit mass placed at that point.
g = Fg
mFg = GmM
r2
g = GMr2
Gravity will get very small with large distances, but is
never zero!
There is no place in the Universe where it is zero!
What is Zero Gravity Then?
Zero gravity occurs when an object is accelerating in a way that makes the normal
force disappear.
Multiple ForcesObjects can experience multiple forces of gravity at once.
The tides are caused by the gravitational pull of the
Moon on the Earth.
Spring tides occur twice a lunar month and are caused when the Earth, Moon, and Sun are all aligned.
It is important to remember that the gravitational equation only gives you the magnitude of the force!
You will need a free-body diagram to determine the direction!
Spring Tides
FEm
FES
FEM =GmmmE
rEM2FES =
GmSmE
rES2
The gravity equation can only look at two objects at a time!
Fg = FEM + FES
Remember! You have to add the sign based on your diagram!
The Asteroid Belt
FEm FAJ
FAM =GmAmM
rAM2
FAJ =GmAmJ
rAJ2
Fg = -FAM + FAJ
The net force is zero so they stay where they are in
orbit around the sun!