Topic 5 - Keywords

Diffusion = Molecules moving from one area of high concentration to an area of low concentration

Volume = The space occupied by an object in 3 dimensions, measures in m3, V= L x h x w

Kelvin (K) = The lowest possible temperature 0K = -273 degrees

Flexible Container = A container that changes its shape depending on the pressure inside or outside it. The volume is variable and the pressure is constant, Example – syringes & pistons.

Kinetic Theory/ Particle Model = A theoretical model of a gas that describes gas molecules by using the kinetic theory. The molecules are assumed to collide elastically with the walls of the container they are in.

Rigid Container = A container that will keep a fixed shape regardless of the pressure inside it or outside it. The volume is constant & pressure is variable. Eg: rigid metal cans & glass bottles.

Brownian Motion = The slow random motion of large, visible particles such as smoke particles. Explained by postulating much smaller faster particles that are not visible, ,such as air particles, that collide with large particles & make them move.

Mass (kg) = In kg of one metre cubed of a substance.

Density = Amount of material in an object, measured in kilograms.

Absolute zero = the units of absolute temperature. 273K = o degrees

Pressure = The effect of a force spread out over an area. P = F/a

Ideal Gas = Any liquid or gas.

PFY questions of Density

Physics For You Questions on Density:

1.       An object has a mass of 100 grams and a volume of 20 cubic centimetres. What is its density?

Density = mass/volume  = 100/20 = 5 g/cm3

2.       An object has a mass of 40000 kilograms and a volume of 5 cubic centimetres. What is the density?

Density = mass/volume = 40,000/5 = 8000 g/cm3

3.       An object has a volume of 3 cubic metres and a density of 6000 kilograms per cubic metre. What is its mass?

Density = mass / volume then mass = density x volume = 6000 x 3 = 18000 kg

4.       A water tank measures 2m x 4m x 5m. What mass of water will it contain?

40 kg

5.       An object has a mass of 20 000 kilograms and a density of 4000 kilograms per cubic meter. What is its volume?

If Density = mass/ volume  then volume =  mass / density  = 20000/4000 = 5 kg

6.       The density of air is 1.3kg/ m3. What mass of air is contained in a room measuring  2.5m x 4m x 10m?  How does the compare with your mass?

=  100 kg  , this is a lot bigger than my mass.

5.3 Plenary

Drag'n'Drop Density (in kg per m3).swf Download this file

Remember: 1g/cm³ = 1,000kg/m³

Density of an irregular solid

Density of an irregular solid:

Method:

 

1.       Measure mass using a balance

2.       Measure volume by using the “displacement” method (submerge solid in a “Eureka” can and collect the overflow in a measuring cylinder)

3.       Calculate density (p (roh) = m / V)

 

 

 

Results:

 

1.       M = 139.6g

2.       V = 66 cm3

3.       P(roh) = m/V = 139.6/66 = 2.12

Obj 5.2 and 5.3 Density

5A1 Teacher Presentation.ppt Download this file

Density of a Regular Solid 5.2

Method:

 

1.      Measure mass using a balance

2.      Measure width, length and height using a ruler

3.      Calculate volume (V= w x l x h)

4.      Calculate density ( p (rho) = m/v)

Results:

 

1.      M= 108.1g

2.      W= 20cm; l= 10cm; h= 2cm

3.      V= 20 x 10 x 2 = 400 cm^3

4.      P (rho) = m/v = 108.1/400^3 = 0.27025 g/cm^3