Physics word problems regarding basic concepts

[jon.physics]

Homework Statement

Explain why a sharp knife cuts better than a dull knife

Homework Equations

None that i know of

The Attempt at a Solution

Not sure where to begin

1. The problem statement, all variable and given/known data
what happens to the density of air in a common rubber balloon when it is heated

2. Homework Equations
none that i know of

3. The Attempt at a Solution
not sure where to begin

1. The problem statement, all variable and given/known data
How does water pressure 1 meter beneath the suface of a lake compare with water pressure 1 meter below the surface of a swimming pool

2. Homework Equations
none that i know of

3. The Attempt at a Solution
not sure where to begin

1. The problem statement, all variable and given/known data
when an air bubble rises in water, what happens to its mass, volume, and density

2. Homework Equations
not sure

3. the attempt at a solution
not sure

I'm sorry but my professor has not been present for the past couple of weeks so I'm confused as to where to begin. This is my first semester taking physics ever and I'm having a difficult time understanding these word problems. any help would be great. thanks

 

[Bob Loblaw]

Pressure=force/area.

A sharp knife has a finer edge which can be read as having less surface area. The force of the cutting is dispersed among a smaller surface. Cutting with a dull knife might not generate enough pressure to tear the molecules apart.

 

[jon.physics]

Thanks I appreciate that. Can anyone help me with the other questions?

 

[Anadyne]

Since you didn't attempt anything yet, I'll only give you hints on where to begin.
2) What's the difference between the lake and a swimming pool? Is there a difference? What would make the pressures different? Is any difference? What kind of factors changes pressure?

3) Think about what happens if its mass changes. If it does change, why does it change? Where would it go? What affects a gas's volume? Surely if the air bubble were stationary (somehow just staying in the same place) its mass and volume would be the same. What changes does rising do, if any? What still stays the same? Density is related to mass and volume, so don't worry about density until you've figured out what happens to the mass and volume.