A wagon is at rest until a girl pulls it along the sidewalk. Which of the following describes the net force experienced by the wagon that causes it to move? a
noncontact
b
gravitational
c
unbalanced
d
balanced

They carry out the exchange of gases as we breathe ( oxygen and carbon dioxide).

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .