Density and Pressure Flashcards
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?
Density
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?
- In 1827, botanist Robert Brown noticed that pollen grains in water moved with a zig zag, random motion
- This type of movement of any particles in suspension is known s Brownian motion It support particle theory of the different states of matter
- 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?
- 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
- The coldest that anything can ever get is -273 degrees Celsius
- This temperature is known as absolute zero
- At absolute zero, atoms have as little kinetic energy as it is possible to get
- Absolute zero is the start of the Kelvin scale of temperature
- 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
- newtonmeter
- scales
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?
- 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)
- Use equation density = mass / volume
