The friction arrow in an FBD for a moving object point is in opposite way to motion. Because friction always works in the opposite direction of the motion of the object.
Answer: Option D
Explanation:
When two object come into contact, the contact force come into play. Now, one component of the contact force i.e. the normal forces act perpendicularly at the direction of motion. Whereas, the frictional forces always acts parallel at the direction of the force acting on the object but in the opposite way.
For example, if we slide a book on the table to the right hand side, the exact equal and opposite frictional force will induce in the opposite direction, tempting to reduce the motion.
carry blood to the brain
B.
return blood to the lungs
C.
help control body temperature
D.
replace old blood cells
Answer:
Its C
I hope this helps!!!
Black Hole
___________
It is the most mysterious thing in our universe.
✳ John Michell was the first scientist who gave his idea on black hole in 1783
✳ later than Pière simon described black holes in his book the system of the world in 1796.
What are black holes?
=> It is also a celestial body which have infinite gravitational force and infinite mass and even light can not escape from it.
=> If any object goes near a black hole then time slows down for that object.
How black holes formed?
=> Mostly black holes formed because of compression of mass and density of stars.
So, first we know how stars formed and then black holes.
= stars are formed by the cloud of gas and dust present in our universe which we simply called as Nebula.
= They are mostly composed of hydrogen and helium with some amount of another elements.
= when the density of nebula decreases then they contract because of their gravitational force and then its temperature rises at very high level and in that temperature hydrogen atom makes helium by fusion reaction and because of the speed of hydrogen atom and also heat the nebula takes a spherical shape which we call star.
Now black hole formation -
= The gravitational force of stats are balanced by their heat.
And hydrogen acts as a fuel for it.
= and when its hydrogen finishes then with passage of time that star cools down and then its mass and density becomes 4 times greater then its original mass and density.
And then that star can't control its gravitational force and then a blast occurs which we call supernova.
And after this blast if any of the piece of that star which have more mass remains then it becomes a star which have mass and density of a critical level and we call this as Neutron star.
In this type of Neutron star because of its gravitational force then it starts contracting and after contracting it at a critical level then it becomes a body which have infinite density and mass and because of this infinte density and mass the space time bents inward there and then it doesn't be there and we call this as a black hole.
Its whole mass is focused at center which we call it
✳ central singularity point
And the boundary of black hole is called
✳ event horizon
And nothing can escape from here even light can't.
And here concept of time doesn't work.
=> According to theory of relativity if the object is near the black hole then the time slows down for it.
Types of black holes
1. Stellar mass black hole
~> It is the type of black hole formed because of contraction of a star which have mass about 3 times greater than the sun.
2. Super massive black holes
~> It is formed in center of any galaxy and have infinite mass and gravitational force and it has mass about 100000000 times that of sun.
3. Permordial or small black holes
~> They are formed because of the more heat at the center of a star and the mass of that star is less than that of our sun.
Physicist think that they formed with the beginning of universe
✳ the nearest black from earth is
cygnus x1