(b) Density and pressure

(b) Density and pressure ​

5.2 know and use the relationship between density, mass and volume: ​

Density is the mass per unit volume of an object or fluid.

density=massvolume

p=mV

5.3 describe experiments to determine density using direct measurements of mass and volume ​

Experiment: To determine the density of a regularly-shaped object. ​

Apparatus: Vernier calipers, ruler, balance

Procedure:

  1. Find the mass, using the balance.

  2. Determine the volume by taking appropriate measurements and then calculating the volume as follows:

(a) cuboid – measure the length, breadth and height by using a metre rule or a pair of vernier calipers V = l x b x h

(b) cylinder – measure the diameter and the length. V = πd24 ×l

(c) sphere – measure the diameter with a pair of vernier calipers or a pair of engineer calipers together with a metre rule. V=43πd23

Calculation: If the mass is in g and the volume is in cm3 then, density=mV g cm-3

Precaution: The precaution which need to be taken when using the vernier calipers and the metre rule apply here.

Experiment: To determine the density of a liquid. ​

Apparatus: Burrete, beaker, balance, retort stand.

Procedure

  1. Find the mass of a clean, dry beaker.
  2. Run a volume of the liquid from the burette into the beaker.
  3. Find the mass of the beaker and the liquid (m2)

Calculation: If the masses are measured in g, and the volume in cm3, then the density of the liquid =m2-m1V g cm-3

=m2-m1V × 1000 kg m-3

Precaution:

  1. When reading the volume of the liquid, make sure that the eye is level with the base of meniscus of the liquid.

  2. Keep the beaker on a plain surface.

Experiment: To determine the density of an irregular shaped object ​

  1. Determine the mass of the object by using a top pan balance.

Now find, find the volume:

  1. Pour some water in a measuring cylinder.
  2. Mark the position of the lower meniscus of the water level.
  3. Put the object into the water. The water level rises.
  4. Mark the position of the lower meniscus again
  5. Subtract the two readings and get the volume of the object.

Density:

  1. Use the equation ρ=mV to find the density.

5.4 know and use the relationship between pressure, force and area: ​

The

ρressure=forcearea

p=FA

5.5 understand that the pressure at a point in a gas or liquid which is at rest acts equally in all directions ​

Pressure in liquids and gases act equally in all directions, as long as the liquid or gas are not moving.

Experiment: To prove the above statement. ​

4 holes are made at the same depth in a can. So when it is filled with water, the water flowing from these holes moves at same speed. This proves that the pressure is equal in all direction.

5.6 know and use the relationship for pressure difference: ​

pressure difference = height × density × g

p = h × ρ × g

Experiment: To investigate that pressure decreases with height. ​

Three holes are made at different height of the can. The water from the hole at the bottom-most of the can travels at highest speed. And the water from top-most hole travels at lowest speed. Thus, proving that pressure increases with depth.

Next: (c) Change of state