1. Gravitational Interactions
CONCEPTUAL PHYSICS
Gravitational Interactions

2. Acceleration due to gravity: downward acceleration due to gravity
Acceleration due to gravity: downward acceleration due to gravity. On Earth g=9.8m/s2
Do not confuse g with G (universal constant)
But there is a relationship between the two.
From the following formulas:
F= ma and F= Gm1m2 d2
g= GM R2
M: mass of planet R: radius of planet

3. Gravitational fields:
The moon interacts with the gravitational field of the Earth
Rockets and space probes interact with the gravitational fields of earth and other planets and stars.
A gravitational field is an example of a force field: something in space experiences a force due to a field.
A magnetic field is an example of another force field.
Earth’s gravitational field is strongest near Earth’s surface and weakens with increasing distance from Earth

4. If a tunnel was drilled at the center of the Earth, we would find out that g=0 in the center. And g is between 0 and 9.8 between the center and the surface.
As you go down, g decreases as you are pulled downward to the center because you are also pulled upward by the other part of earth above you. At center, the net force is 0, so g =0.

5. Weight and weightlessness
The force of gravity gives us the sensation that something presses us against Earth rather than something that accelerates us. We interpret this as weight.
In a scale, the weight reading on the scale is linked to the amount of compression of the springs inside when you step on the scale.
In an elevator accelerated upward, the scale push harder on your feet compressing the springs even more showing an increase in weight.
In an elevator accelerated downward, the scale push less on your feet compressing the springs less and the scale would show a decrease in your weight.

6. It is more practical to say that weight is the force you exert against a supporting floor (or weighing scales)
Weightlessness is not the absence of gravity, rather, it is the absence of a support force.
Astronauts in orbit are without a support force and are in a sustained state of weightlessness.
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7. Ocean tides: It has been known that there was a connection between the ocean tides and the moon
Ocean tides are caused by differences in the gravitational pull of the moon (and the sun) on opposite sides of Earth.
The oceans nearest the moon is pulled upward toward the moon , while the main body of Earth is pulled toward the moon also- away from the ocean on the far side. Earth’s water get elongated slightly at both ends, causing what we know as tides.
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8. Lunar eclipse: Earth is directly between the sun and the moon.
Solar eclipse: moon is directly between the sun and Earth.
Neap tides: when we see half-moon, the tides due to the sun and moon partly cancel each other and we see high tides lower than average.
Black holes: When a star runs out of fuel for fusion, it collapses under gravitational forces. Very massive stars collapse to form black holes.
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9. 1) In the Little Prince, the Prince visits a small asteroid called B612. If the asteroid B612 has a radius of only 20.0m and a mass of kg, what is the acceleration due to gravity on asteroid B612?

10. The mass of a star is somehow doubled without any change in its radius
The mass of a star is somehow doubled without any change in its radius. How does gravitational field at its surface change?
The mass of a star increases by a factor of four, while its radius doubles. What happens to the gravitational field at its surface?

11. Gravitational Interactionos
CONCEPTUAL PHYSICS
Gravitational Interactionos