Aaircraft strut consists of two cylindrical portions ab and bc and is restrained at both ends. portion ab is made of 7075-t6 aluminum (eal = 10.4 msi, αal = 13.1 x 10-6 /°f) and portion bc is made of 6al-4v titanium (eti = 16.5 msi, αti= 5.3 x 10-6 /°f). if the strut is initially unstressed but is then subjected to a temperature rise of 70°f, determine the normal stresses induced in portions ab and bc by the temperature rise.

scientific laws are the result of testing theories and proving them to be facts.

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.