A chemical change occurs when . there is a change in the shape of a substance
there is a change in a state of a substance
there is a large increase in the size of the substance
there are one or more new substances with new properties formed

There are one or more new substances with new properties formed.

Explanation:

Its a chemical change when a new substance is created with new properties.

Iron Rusting is an example since it cant revert into it's past form.

in the analysis of systems that involve fluid flow, we frequently encounter the combination of properties u and pv.

weight of any object is given by

w = m*g

where m is mass of the object and g is the acceleration due to gravity.

for earth the value of g is 9.8 m/s^2 so

w=117.6 n m=12 g=?

117.6=12g => g=9.8 m/s^2

which is the force of gravity on earth.