Heat can be transferred through conduction, convection, and radiation. What is necessary in order for heat to be transferred by
conduction? A.
Heat must be transferred through space.
B.
Heat must be transferred in the form of currents.
C.
The substances must be liquids or gases.
D.
The objects must be in direct contact with one another.
Conduction is a mode of heat transfer where thermal energy flows between bodies that are in direct contact. Thus, the correct answer would be D.
A is incorrect here: heat flow via conduction involves high-energy particles (such as atoms or molecules) having their energy transferred to neighboring particles by contact or collision. If “space” refers to a region that contains only gas (the everyday understanding of “space”), then heat transfer by conduction would be extremely inefficient since gas molecules are so far apart. If “space” refers to a vacuum, then conduction cannot occur at all (radiation is the only mode of heat transfer through a vacuum). In either case, not only does conduction not necessitate space, but space impedes heat transfer by conduction.
B is incorrect because conduction operates via the movement of energy itself and not of matter (although, as we established above, the presence of matter is necessary for conduction). Conductive heat transfer can occur within a body itself (a metal bar that is heated on one end will eventually become hot on the other end). So, apart from being definitionally incorrect, conductive heat transfer doesn’t require currents at all. This mode of heat transfer occurs in convection.
C is manifestly incorrect: conductive heat transfer can occur between or within solids, so it can’t possibly be necessary that the “substances . . . Be liquids or gases.
If the object is falling straight down it is in free fall. The difference between that and two-dimensional motion is that 2D motion is parabolic (projectile)
