# Three big questions about Gravity, Cold and Magnets

1. Mar 15, 2015

### cubby208

Hey, So I am a sophomore in high school and have never taken a physics class before (it hasn't been offered) but I look forward too taking one.

I got really thoughtful today and came up with three questions.

1. Gravity... is it energy? And is it infinite? I mean we harness gravities energy in things like water turbines. Gravity makes the water move and turbines turn it into electricity. What does this mean?

2. Is cold really the absence of energy? Can it be harnessed? The reason I ask is their is some sort of theory I heard and i might be terribly simplifying but basically "everything moves to a state of chaos without the input of energy". Now I know cold means particles are not moving as much but could that only be a lack in kinetic energy? For example cold moves water which is in a turbulent state into a more organized crystalline structure. Now I know hydrogen bonds cause the crystal structure but it that all the energy that goes into making that happen?

3. Are magnets infinite energy. I mean they seem pretty long lasting to me and push away other things in a kinetic form... What is this? If we somehow managed to get two massive focused magnets and force them into each other to the point where they were touching... could we harness energy from that? Specifically the magnetic resistance?

Thanks so much for reading! Pardon my stupidity and lack of lingo/vocab on these things.

2. Mar 15, 2015

### cubby208

Hey also. Which AP physics has to do with laws of motion and collision. I am interested especially in these fields because it would be fun to be a physics programmer.

3. Mar 15, 2015

### Staff: Mentor

Welcome to PF!

#1 and #3 are the same. Magnetism and gravity are forces (or fields of forces). Force isn't energy. A book sitting on a table has forces applied to it by gravity and by the table, but it doesn't get hot because there is no energy expenditure. You can generate energy by moving (force and distance) through one of those fields. A hydroelectric turbine works when water falls -- but then something has to move the water back up to the top of the dam or it will stop. Think about what might do that.

For #2, yes, "cold" is a relative absence of thermal energy. All thermodynamic processes use a "hot" reservoir and a "cold" reservoir, and harness the heat energy flowing between them (not unlike the hydroelectric dam does for gravitational potential energy).

4. Mar 16, 2015

### gleem

Cold does not move anything. Coldness is a state of relative lower energy as indicated by temperature. This reduced energy condition may allow other process to occur. since excess energy may produce forces that interfere with those processes. For example as you noted the crystallization of water cannot fundamentally occur above some critical temperature and pressure because the crystallization process is being dismantled so to speak by stronger external forces. imagine trying to assemble something while your hands are shaking.