Answer:If an object's speed changes, or if it changes the direction it's moving in,
then there must be forces acting on it. There is no other way for any of
these things to happen.
Once in a while, there may be a group of forces (two or more) acting on
an object, and the group of forces may turn out to be "balanced". When
that happens, the object's speed will remain constant, and ... if the speed
is not zero ... it will continue moving in a straight line. In that case, it's not
possible to tell by looking at it whether there are any forces acting on it
Answer:
B. Same for a chemical family
What do we know that might help here ?
-- Temperature of a gas is actually the average kinetic energy of its molecules.
-- When something moves faster, its kinetic energy increases.
Knowing just these little factoids, we realize that as a gas gets hotter, the average speed of its molecules increases.
That's exactly what Graph #1 shows.
How about the other graphs ?
-- Graph #3 says that as the temperature goes up, the molecules' speed DEcreases. That can't be right.
-- Graph #4 says that as the temperature goes up, the molecules' speed doesn't change at all. That can't be right.
-- Graph #2 says that after the gas reaches some temperature and you heat it hotter than that, the speed of the molecules starts going DOWN. That can't be right.
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