What happens to particle motion when the heat is added? how do you suppose this would affect the rate at which a chemical change takes place?

Explanation:

When heat is added to an object it's internal energy increase. What is meant by internal energy is the kinetic energy and potential energy of the particles in an object. Potential energy of particles is according to the structure of particle arrangement within the object.

As kinetic energy increases the motion of the particles within the molecule increases therefore the speed of the particles inside the object increases, so the probability of atoms interacting with each other to produce new substance also increases. So the rate of chemical reaction increases.

Actually what we feel as heat is a measurement of the amount of kinetic energy the particles in the object have.

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.