Re: How can the freezing point and the melting point of a substance be the same

The freezing point and melting point are the same temperature on a 
thermometer.  Above that point, the substance is a liquid.  Below
that point, the substance is a solid.

I think that what you are asking is, "How can a material melt at the
same temperature that it freezes, since melting and freezing are 
opposites?"

That's because the material will melt if you heat it up, and pass that 
magic temperature.  It will freeze at that same temperature when you
cool it down again.  So it all depends on what the substance is going
to do when you reach that temperature.

Now, if you're exactly at that temperature, you have....slush.  It's
hard to tell if the substance was a liquid that is now freezing, or 
a solid that is now melting.  In that case, you can argue until the cows
come home about whether it is a melting point or a freezing point