Consider a hypothetical crystalline metal. as the temperature is raised from 800 to 1000k, the lattice parameter increases 0.05% due to thermal expansion and -the density decreases by 0.16%. this density decrease is due to the combination of thermal expansion and vacancy creation a) what is the expected percentage decrease in density due to normal thermal expansion alone? thus you can calculate volume per unit cell increase by 3 times the lattice parameter increase) (2) (hint: for simplicity in calculation, the expansion of unit cell is relatively small in this case, b) evaluate the net density decrease due to vacancy production alone. (2) c) if the vacancy concentration at 800k is 106, estimate the activation energy for vacancy production.

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.

hi,

what occurs during a solar eclipse?

there are small tides across earth.

the moon is between earth and the sun.

p.s. im not sure if the first answer is correct because during a solar ecliphse there are spring tides and i dont know if they are the same.