The sun has sufficient hydrogen to continue fusing into helium for how much longer?

4500 million years

Explanation:

The Sun shines thanks to the thermonuclear conversion of hydrogen to helium inside. It is currently 4,500 million years old and has reservations for a similar period of time. When this fuel is exhausted in the central region, the heart of the Sun, constituted of helium and in an inert state, will contract and put more external fuel reserves within reach of the star, with which this mass of helium will grow over time . When that happens, the Sun will evolve into a giant star that will reach the orbit of Mars and, therefore, destroy the planet Earth.

As the helium heart mass increases so do the central density and temperature. When it reaches 100 million degrees, helium fuses thermonuclearly with itself and becomes a mixture of carbon and oxygen.

When the helium runs out in the center, the previous operation is reproduced approximately. The carbon / oxygen heart contracts and the helium and hydrogen of the surrounding layers are placed within the reach of thermonuclear combustion. The difference is that this double combustion is unstable and the density is so high that electrons can, alone, stabilize the heart of carbon and oxygen. The end result is that the outer layers, which originate a planetary nebula, are expelled, and the old thermonuclear reactor becomes visible, which becomes a white dwarf that slowly cools like the embers of a fire over billions of millions. of years.

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.