section 5: Solids, Liquids and Gases

Question 1

important units:

Answer 1

-degrees Celsius (ºC)
-Kelvin (K)
-joule (J)
-kilogram (Kg)
-kilometre/metre^3 (kg/m^3)
-metre (m)
-metre^3 (m^3)
-metre/second (m/s)
-metres/second^2 (m/s^2)
-newton (N)
-pascal (Pa)

Question 2

formula linking density, mass and volume

Answer 2

-the density of a substance is defined as the mass per unit volume and is measured in kilograms per metre cubed (kg/m^3)
density = mass/volume
p = m/V

Question 3

practical: investigate density using direct measurements of mass and volume

Answer 3

1. to measure the density of a substance, use a balance to measure its mass
2. if it’s a box shape, start by measuring its length, width and height with an appropiate piece of equipment (e.g. ruler). Then calculate its volume by multiplying the length, width and height together
3. for an irregular solid, you can find its volume by submerging it in a eureka can filled with water. The water displaced by the object will be transferred to the measuring cyclinder
4. record the volume of water in the measuring cylinder, this is also the volume of the object
5. plug the object’s mass and volume into the density fomula

Question 4

formula linking pressure, force and area + knowledge:

Answer 4

-pressure is defindes as the force per unit area and is measured in Pascals (Pa)
pressure = force/area
p = F/A
for example, lying down on a bed of nails compared to a single nail:
-the force applied is the weight of you body
-the total area is either a single pin point or many points spread out over a larger area
-therefore, on a bed of nails, the pressure is lower as the area is greater

Question 5

pressure at a point in a gas or liquid:

Answer 5

-the pressure at a point in a gas or liquid at rest acts equally in all directions and causes a force at right angles to any surface
-pressure in a fluid (gas or liquid) is created from the movement of particles (as they collide with a surface)

Question 6

formula linking pressure difference, height density and gravitational field strength + knowledge:

Answer 6

-the pressure beneath a liquid surfaces increases with depth, the density of the liquid and the gravitational field strength
-it is given by:
pressure difference = height x density x gfs
p = pgh
-deeper in the fluid the more particles above the point, hence the greater their weight
-fluids with higher density have more particles per unit of volume, hence greater weight
-weight depends upon gravitational field strength

Question 7

ideal gas molecules: molecules

Answer 7

-gas molecules move rapidly and randomly due to collisions with other gas molecules
-gases exert pressure on a container due to collisions between gas molecules and the wall
-when the molecules rebound off the walls, they change direction so their velocity and therefore momentum changes
-this means they exert a force because force is equal to the change in momentum over time

Question 8

ideal gas molecules: pressure and temperature

Answer 8

-at a constant volume, if the temperature increases, the pressure increases because the molecules move faster so they collide harder and more frequently with the walls
-the temperature at which the pressure is zero is called absolute zero (-273ºC), the Kelvin scale of temperature defines absolute zero to be 0K with an increment of one Kelvin equal to an increment of one degree Celsius, this means that:
-temperature in kelvin = temperature in degrees celcius + 273
-for a gas at fixed mass and volume, where the temperature is measure in Kelvin:
P1/T1 = P2/T2 pr P/T = constant
-at a constant temperature, if the volume increases, the pressure decreases because the molecues collide less frequently with the walls and over a greater area
-for a gas at fixed mass and temperature:
P1V1 = P2V2 or pV = constant

Question 9

Boyle’s Law:

Answer 9

-the temperature in Kelvin of a gas is proportional to the average kinetic energy of the molecules
-the higher the temperature, the greater the average kinetic energy and so the faster average speed of the molecules