10- Fluids (density and pressure)

Question 1

density

Answer 1

• represented as rho (curled ‘p’)
• same symbol as resistivity
• measured in kgm^-3
• p = mass/ volume (in solids)

Question 2

important densities

Answer 2

• water = 1000kgm^-3
• mercury = 13600kgm^-3
• ethanol = 790kgm^-3
• air = 1.34kgm^-3

Question 3

pressure

Answer 3

• density of gasses must also be given with temperature and pressure, as they affect it
• atmospheric pressure is 1.01*10^5 Pa
• pressure in a fluid is calculated by height from surfacedensity of fluidg (units are pascals)
• if h is large and the fluid is a gas, density lowers towards the higher values of h than at the bottom

Question 4

Flotation

Answer 4

• in fluids, objects displace their equivalent amount of mass in fluid. Flotation is when the object does this without being fully submerged
• upthrust is caused by the pressure below an object being greater below it than above it, and is equivalent to the weight of any displaced fluid
• more dense fluids (i.e cold ones) require less displacement for flotation. Salt water is more dense than fresh water, so boats float higher in it.