Solids, Liquids And Gases - Part 2 (T5) Flashcards
Explain what “Brownian motion” is an how it came about..
Named after the Scottish botanist Robert Brown (1773-1858). In 1827 he was observing pollen grains in water and noticed the grains seemed to jerk around in random movements. At first he thought this was due to to a kind of life force in the pollen, but he also observed other tiny non-living particles in water and found they moved in a similar way. A similar effect is seen with particles in a gas.
Brownian motion was not explained until the theory that all substances are made from particles was developed.
Particles of a liquid or gas are moving around continuously and bump into each other and into tiny particles such as pollen grains. Sometimes there will be more collisions on one side of a pollen grain than on another, and this will make the pollen grain change its direction or speed of movement.
What is a Eureka Can and how is it used to determine the volume of an irregular solid?
Also known as a displacement can, it is essentially a can with a spout on top. It is filled with water up to just below the spout opening. An object is placed in the can and water is displaced through the doubt, into a measuring cylinder. The volume of water in the measuring cylinder is the volume of the object.
How do you weigh a liquid?
You can fill a measuring cylinder with the liquid, after you have already weighed the cylinder. Then weigh the measuring cylinder with the liquid in it, deduct the weight of the cylinder itself and that is the weight of the liquid.
In physics, how do you calculate pressure?
P = F / A
Where:
P = pressure in Pa F = force in N A = area in m2
Explain what is meant when we say the molecules in a gas have random motion
They move around in straight lines at a wide range of speeds. Each one moves around at a constant speed until it collides with another molecule, or the side of the container. When two gas molecules collide, they bounce off each other and their speeds will change, BUT the total kinetic energy of the two molecules will stay the same because the faster one tends to slow down the slower one tends to speed up.
In a hot gas, is the average speed of the molecules faster or slower than in a cold gas?
Faster
Explain the ‘Brownian motion experiment’ and how it demonstrates the random motion of air molecules..
It uses smoke and a microscope. If you illuminate smoke under a bright light and examine it at a low magnification you will see it is not a gas but is made up of microscopically small pieces of solid (carbon). If
You will see each smoke particle zigzags around, changing direction and speed several times per second without appearing to collide with any other smoke particles. The conclusion is the particles are being constantly bombarded by invisible particles which are causing the zigzag motion - these invisible particles are air molecules.
What is ‘absolute zero’ and what effect will it have on gas molecules, considering the fact that heating them up increases their average speed?
If the temperature is gradually reduced there will come a point when the molecules actually all stop moving. At this temperature the molecules have zero total kinetic energy so it is not possible to extract any more heat energy from them. They have reached the coldest temperature that is it possible to reach - Absolute Zero. Nothing can go down to a lower temperature than this, no matter what.
What temperature is Absolute Zero?
-273 degrees centigrade (to the nearest whole number)
How do you convert the kelvin temperature to degrees Celsius?
The kelvin temperature starts at absolute zero which is -273 degrees C.
So to convert from Celsius to kelvins simply add 273 and to convert from kelvins to Celsius simply subtract 273.
The Kelvin scale helps us to make more sense of physics theories because the average kinetic energy of the molecules in a gas is proportional to the temperature in kelvins. Why can this statement not be true if you use the Celsius or any other scale?
Because they all involve some negative values
