SOLIDS, LIQUIDS AND GASES Flashcards
1
Q
What is density?
A
Density is a measure of how much matter (or stuff) there is in a certain size (or space).
2
Q
Density key facts?
A
- Objects float if their density is less than, or the same as, the density of the substance surrounding it.
- If density is greater – the object will sink.
- In scientific terms, DENSITY is how much MASS there is in a given VOLUME of a substance
3
Q
Unit of density?
A
- kg/m3 if we use: mass (kg) & volume (m3)
- or g/cm3 if we use: mass (g) & volume (cm3)
4
Q
Density of water?
A
1000 kg/m3 or 1 g/cm3 (divide by 1000)
5
Q
Density equation?
A
- density= mass÷ volume
- ρ=m/V
ρ = density (kg/m3) m = mass (kg) V = volume (m3)
- This can be rearranged to give: m = ρV or V = m/ρ
- Unit of density is sometimes given in g/cm3
6
Q
Measuring the density of a substance?
A
- Just use the scales or balance to finding the mass of an object (grams)
- The volume of a regular shaped object (like a block) is length x width x height in cubic centimetres (cm3)
- The volume of an irregular shaped object, can be found by how much volume of water is displaced from a full Eureka (or displacement) can.
- For liquids, just use a measuring cylinder for volume.
7
Q
What is pressure?
A
Pressure is a measure of how much force is applied (and spread) over a certain area.
8
Q
Pressure key facts?
A
- As you in increase the size of the force you increase the size of the pressure.
- As you increase the size of the area over which a force acts, you decrease the pressure.
9
Q
Pressure equation?
A
-P = F/A
P = Pressure – measured in Pascals (Pa) or N/m2 F = Force – measured in Newtons (N) A = Area – measured in square metres (m2)
- This can be rearranged to give: F = pA or A= F/p
- Pressure can be expressed as N/cm2 if the area is small
10
Q
What is atmospheric pressure?
A
-Atmospheric pressure is the pressure caused by air particles all around us. It acts in all directions on an object – not just from the top!
- Suck out the air from a can and it will collapse, but to the outside atmospheric pressure.
- We don’t squash because we have pressure inside us which pushes out!
11
Q
Liquid pressure?
A
- The pressure on objects under water is similar to that of atmospheric pressure.
- It acts in all directions.
- Atmospheric pressure still acts on them, but now you have extra pressure due to the water above them.
- The height of the water above, adds a pressure difference!
- It is due to a column of liquid depends on height of the liquid column above.
- Angle, shape, column width, surface area do not matter for the pressure difference due to a column of liquid.
- Only the column height and the weight of liquid above (linked to density) affects pressure
- The equation which is used to calculate this additional pressure difference, uses these relationships
12
Q
Pressure difference equation?
A
- pressure difference (p) = height (h) x density (ρ) x gravitational field strength (g)
- p = hρg
p = pressure (Pa or N/m2) h = height (m) ρ = density (kg/m3) g = gravitational field strength (N/kg) (g = 10 N/kg on Earth)
-This can be rearranged to give:
h = p/ρg or ρ = p/hg or g = p/hρ
13
Q
Gas particles?
A
- Gas molecules are in constant random motion. They move in different directions with different speeds.
- The temperature of a gas is related to the average kinetic energy of the molecules.
- The higher the temperature the greater is the average kinetic energy, and the faster the average speed they move!
14
Q
What causes gas pressure?
A
- When the particles collide with the wall of their container, they exert a FORCE on the wall.
- The TOTAL FORCE (F) exerted by all of the molecules inside the container on a unit area (A) of the walls is the gas PRESSURE (since p = F/A).
15
Q
Pressure can be increased by?
A
- Making the volume smaller, so the particles hit the walls more frequently
- Increasing the temperature, so they have more energy, move faster and so hit the walls with more force and more frequently as well.
- Increase the number of particles, so more will collide with the wall
