Density and Pressure Flashcards Preview

Physics GCSE > Density and Pressure > Flashcards

Flashcards in Density and Pressure Deck (34):

What is the equation for density?

density = mass / volume
p (rho) = m / v
Kg/m3 or g/cm3 = Kg/g / m3/cm3
-1g/cm3 = 1000kg/m3
-Density does not vary with size or shape
-The average density of an object determines whether it floats or sinks
-A solid object will float on a fluid if it has a lower density than that fluid


How do you measure the volume of an irregularly shaped object?

Use a displacement can and the water displaced by the object is caught in a measuring cylinder so that its volume can be measured


What does pressure depend on?

Vertical height (and density) NOT on the area


How can you measure the excess pressure of the gas supply?

U-tube manometer, can also be used to measure the pressure of the atmosphere with a mercury barometer


What does density depend on?

What an object is made of not size or shape


How do you work out pressure?

Pressure = force/area
Pa (pascals) = N/m squared


What happens if the same force is applied on a larger area?

Creates lower pressure


What is the pressure like is gases and liquids?

-The pressure at any point acts equally in all directions
-The pressure increases with depth
-The pressure is higher at the bottom of trhe sea than at the surface and it is lower high up in the atmosphere than close to the Earth


What does pressure difference in liquids and gases depend on?



What is pressure difference?

Is the difference in pressure between two points in a liquid or gas


How do you work out pressure difference?

Pressure difference = height x density x g
Pa = m x kg/m cubed x g


How is kinetic energy related to temperature?

-Kinetic energy is proportional to temperature
-Particle theory says that gases consist of very small particles which are constantly moving in completely random directions. The particles hardly take up any space, most of the gas is empty space
-The particles constantly collide with each other and with the walls
-If you increase the temperature of a gas, you give its particles more energy
- As you heat up a gas, the average speed of its particles increases. Anything that is moving has kinetic energy


How does Brownian Motion support particle theory?

1. In 1827, botanist Robert Brown noticed that pollen grains in water moved with a zig zag, random motion
2. This type of movement of any particles in suspension is known s Brownian motion It support particle theory of the different states of matter
3. Large, heavy particles (e.g. smoke) can be moved with Brownian motion by smaller, lighter particles (e.g. air) travelling at high speeds, which is why smoke particles in air appear to move around randomly when you observe them in the lab


What is absolute zero?

1. If you increase the temperature of something, you give its particles more energy they move about more quickly or vibrate more. In the same way, if you cool a substance down, you are reducing the kinetic energy of the particles
2. The coldest that anything can ever get is -273 degrees Celsius
3. This temperature is known as absolute zero
4. At absolute zero, atoms have as little kinetic energy as it is possible to get
5. Absolute zero is the start of the Kelvin scale of temperature
6. A temperature change of 1 degrees C is also a change of 1 kelvin. The two scales are pretty similar, the only difference is where the zero occurs


How do you convert degrees Celsius to kelvins?

Add 273


How do you convert kelvins to degrees Celsius?

Subtract 273


How is particle theory and pressure in gases related? How is pressure and Kelvin temperature for a gas in a sealed container related?

-Particle theory says that colliding gas particles create pressure
1. As gas particles move about, they randomly bang into each other and whatever else gets in the way
2. Gas particles are very light but they are not massless
3. When they collide with something they exert a force on it and their momentum and direction change
4. In a sealed container, gas particles smash against the containers walls , creating an outward pressure
5. This pressure depends on how fast the particles are going and how often they hit the walls
6. If you heat a gas, the particles move faster and have more kinetic energy. This increase in kinetic energy means the particles hit the container walls harder and more often, creating more pressure
-In fact temperature (in K) and pressure are proportional, so if you double the temp, you will double the pressure
7. If you put the same amount of gas in a bigger container, the pressure will decrease because there will be fewer collisions between the gas particles and the container's walls. When the volume is reduced, the particles get more squashed up and so they hit the walls more often, hence the pressure increases


What is the relationship between pressure and volume and a constant temperature?

pressure x volume = constant
pV = constant
p1V1 = p2V2
(where p1 and V1 are your starting conditions and p2 and V2 are your final conditions)
-This all applies to so-called ideal gases, which are gases are 'well behaved'


Explain how Brownian motion provides evidence that air is made of small particles

For example smoke particles (a large particle) move with random morion and have collisions with smaller (invisible) particles


Which piece of apparatus should the student use to measure his weight?

-weighing scale
-electronic/electric balance


What is the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume?

P1/T1 = P2/T2


What is the Kelvin temperature of the gas proportional to?

-The average kinetic energy of its particles
-If you double the temperature, measured in Kelvins, you double the average kinetic energy of the particles


What is pressure?

Pressure is a measure of the force being applied to the surface of something


How do you determine the density of the object?

1. Take direct measurements of the mass and volume using top-pan balance and if can't volume then immerse in water and see about of water displace (only works if object is denser than water and so sinks)
2. Use equation density = mass / volume


What do molecules of gas have?

Have a random motion and that they exert a force and hence a pressure on the walls of a container


What does an increase in temperature result in?

An increase in the average speed of gas molecules


Describe the properties of solids

1. Strong forces of attraction hold the particles together in a fixed regular arrangement
2. The particles do not have much energy so they can only vibrate about their fixed position


Describe the properties of liquids

1. There are weaker forces of attraction between the particles
2. The particles are close together, but can move past each other, and from irregular arrangements
3. They have more energy than the particles in a solid and they move in random directions at low speeds


Describe the properties of gases

1. There are almost no forces of attraction between the particles
2. The particles have more energy than those in liquids and solids and they are free to move
3. They travel in random directions and at high speeds


How can kinetic theory explain the three states of matter?

1. The three states of matter are solids (ice), liquids (water), gases (water vapour) and the particles of a substance in each state are the same, only the arrangement and energy of the particles are different
2. When you heat a liquid, the heat energy makes the particles move faster and eventually when enough of the particles have enough energy to overcome their attraction to each other, big bubbles of gas form in the liquid, (BOILING)
3. Similar when you heat a solid and the heat energy makes the particles vibrate faster until eventually the forces between them are overcome and the particles start to move around (MELTING)
4. The melting point of a chemical is the temperature at which it turns from solid to liquid and the boiling point id the temperature at which a liquid becomes a gas


Describe how evaporation works

1. Evaporation is when particles escape from a liquid and become gas particles
2. Particles can evaporate from a liquid at temperatures that are much lower than the liquid's boiling point
3. Particles near the surface of a liquid can escape and become gas particles only in certain conditions


What are the conditions needed for the particles near the surface of a liquid to escape and become gas particles?

1. The particles must be travelling in the right direction to escape the liquid
2. The particles must be travelling fast enough (have enough kinetic energy) to overcome the attractive forces of the other particles in the liquid
-(near enough the surface)


Describe the process of evaporation

1. The fastest particles, (with the most kinetic energy) are most likely to evaporate from the liquid, so when they do the average speed and kinetic energy of the remaining particles decreases
2. This decrease in average particle energy means the temperature of the remaining liquid falls and the liquid cools
3. This cooling effect can be really useful, for example you sweat when you exercise or get hot and as the water from the sweat on your skin evaporates, it cools you down


How is pressure and Kelvin temperature for a gas in a sealed container related? (textbook)

1. The number of gas particles and the space or volume they occupy remain constant
2. When we heat the gas the particles continue to move randomly but with a higher average speed, so the particles have gained energy
3. This means that their collisions with the walls of the container are harder and happen more often
4. This results in the average pressure exerted but he particles increasing
-When we cool a gas the kinetic energy of its particles decreases. The lower the temperature of the gas the less kinetic energy its particles have and so they move more slowly and at absolute zero the particles have no thermal or movement energy, do they cannot exert a pressure