Explain why most materials become less dense as their temperature is increased?

Answer 1

Because the potential that keeps atoms in place is not symmetric. Increasing the temperature of the material, the energy of the atoms increases and because of that non-symmetricity the equilibrium point of their thermal oscillations shifts. That is a boring way of saying that volume of the material increases. Therefore with increased volume and same mass, we have lower density.

Answer 2

As everybody else is saying, as materials heat up, they acquire more kinetic energy. That causes the molecules to vibrate faster. The molecules aren't actually getting bigger, they're just bouncing around faster (picture a group of hyper toddlers: they take up more room than the same number of sleeping toddlers). The material itself expands because of this, but it maintains the same mass, so the density (mass divided by volume) decreases. Also, somebody said that water gets denser when it freezes; that's not actually true. Ice is significantly less dense than water, which is why it floats. The reason for this is that, while the molecules aren't moving around as energetically, water crystallizes when it freezes. That crystal structure takes up a LOT of space, which is why glass bottles full of water burst when they freeze.

Answer 3

Most materials expand when heated, this means their volume increases. The mass stays constant, and since desity=mass/volume, this increase in volume shrinks the density.

Answer 4

The increase in temperature to a substance, take marshmallows for example, will increase the volume. The molecules spread out because they are more energized. The molecules will go faster and spread out. This decreases the density.

Answer 5

Most materials expand when they are heated, this increases their volume but not their mass.

Answer 6

because that is obvious