OCR Physics A G484 Jan 2012 - The Newtonian World

as pv is directly prop to T, this means that as the pressure and volume decreases, the temperature also decreases until a theoretical minimum of absolute zero where there is no pressure and volume.?

Should i get my coat?

So Am I right?

Reply 381

Beresford George

Original post by Jetblast

So Am I right?

Yeah thats right :smile:

Sometimes you also have to talk about their being no kinetic energy due to the velocity of the object being 0, when at absolute 0. However there is minimum potential energy (electrical) meaning that there is still energy inside the object, however no more energy can be taken from the object. (hence absolute zero)

Reply 382

PeterStoba

How would everyone define the mole? I have a feeling that this will be asked, I'm not sure on the exact definition.

Also, anybody know (or guess) exactly what experiments we need to know? Brownian motion, SHC, any others?

Reply 383

ChrisA7x

Just written the important definitions (pretty sure they're 100% correct) :biggrin:

Newtons 1st law: An object will remain at rest or at constant velocity unless acted on by an unbalanced force

Newtons 2nd law: Force is directly proportional to the rate of change of momentum; force is in the same direction as acceleration.

Newtons 3rd law: When two objects interact, the forces they exert are equal and opposite.

Conservation of linear momentum: Total momentum is conserved

Perfectly elastic collision: Momentum and Kinetic Energy are conserved

Inelastic collision: Momentum is conserved. Kinetic energy is lost in the form of heat/sound

Impulse: Change in momentum (area under a force/time graph)

Gravitational field strength: The gravitational force exerted per unit mass at a given point

Keplars third law: The square of the time period is directly proportional to the cube of the orbital radius

Geostationary satellites: Have an orbital time period of 24 hours and orbit above the equator

SHM: Acceleration is directly proportional to the displacement, and the acceleration always acts to the equilibrium position.

(The conditions needed for SHM are: a mass that oscillates, a restoring force, an equilibrium position)

Resonance: when there is a driving force causing something to vibrate at its natural frequency. The oscillations are big in amplitude.

Good examples of resonance:

Cooking – microwaves cause the water molecules in the food to vibrate

MRI – X-rays cause the nuclei to vibrate

Swings – intermittent pushes cause the swing to oscillate with higher amplitude

Bad examples of resonance:

Building bridges – people walking/or wind, causes the bridge to vibrate

Building structures – earthquakes can cause buildings to vibrate at their natural freq.

Brownian motion: Smoke particles moved haphazardly

Pressure: Particles have kinetic energy, therefore there are collision with the container. Collisions cause a force to be exerted on the container.

Pressure=force/area

Specific heat capacity: the amount of energy required to raise the temperate of a mass of 1kg by 1K

Latent heat of fusion: The amount of energy required to melt a substance at constant temperature.

Latent heat of vaporisation: The amount of energy required to boil a substance at constant temperature.

Internal energy: the sum of the random kinetic and potential energies of its atoms

SHC experiment: Measure initial and final temp, current, voltage, time, mass of substance. Determine the energy supplied by w=IVt, and rearrange the shc equation into c=E/m(deltatheta). Limitations: some energy might be dissipated into the surroundings, or absorbed by the container and heating itself up.

1 Mole contains Na particles (avagadro constant)

Boyles law: pressure is inversely proportional to volume for a fixed mass of gas at constant temperature

Kinetic theory of gases:
1) A gas contains a very large number of randomly moving particles
2) No intermolecular forces
3) Volume of the particles is negligible compared to the volume of the gas
4) All collisions are elastic
5) Particles move in straight lines and constant velocity, except for during a collision.

The mean translational kinetic energy of an atom of an ideal gas is proportional to the thermodynamic temperature

Reply 384

Ouzo

Anyone know what we are meant t do with sig figs??

In all the past papers it seems to be completely random how many they do it to?! I though it depended on how many you were gave in the original question, but seems to be completely random, and doesn't say allow any more or less accurate on the majority of mark schemes.

Reply 385

just george

for newtons first law, i would say "An object will remain at rest or at constant velocity unless acted on by an external force"
rather than "unbalanced" ?

Reply 386

Stevo F

18

Original post by ChrisA7x

2) No intermolecular forces

Just quickly skimmed through it, not sure this would get you the mark cause in the mark scheme of the last paper i did it said that inter-molecular forces included forces when particles collide, whether that be right or wrong.

Reply 387

just george

Original post by Ouzo

Anyone know what we are meant t do with sig figs??

In all the past papers it seems to be completely random how many they do it to?! I though it depended on how many you were gave in the original question, but seems to be completely random, and doesn't say allow any more or less accurate on the majority of mark schemes.

These seem to be a bit dodgy to me :L i think just put to the same number of significant figures as the least accurate value given in the question, but if you are reading off a graph that each square goes up say 0.1, do you do it to 1 decimal place? im not sure

Reply 388

Stevo F

18

Original post by ChrisA7x

Newtons 3rd law: When two objects interact, the forces they exert are equal and opposite.

Also, may want to put "and of the same type" here just to be safe

Reply 389

wibletg

3

Original post by PeterStoba

How would everyone define the mole? I have a feeling that this will be asked, I'm not sure on the exact definition.

Also, anybody know (or guess) exactly what experiments we need to know? Brownian motion, SHC, any others?

1 mole contains the same number of particles as there are in 12g of carbon-12 atoms by definition.

Reply 390

Stevo F

18

Original post by just george

These seem to be a bit dodgy to me :L i think just put to the same number of significant figures as the least accurate value given in the question, but if you are reading off a graph that each square goes up say 0.1, do you do it to 1 decimal place? im not sure

Always give back the number of sig figs they give you, it's all you can do really, and remember that something like "200"or "20" given in the question is only 1 sig fig.

Reply 391

singh224

8

Original post by wibletg

1 mole contains the same number of particles as there are in 12g of carbon-12 atoms by definition.

do we need to know this?

Reply 392

Stevo F

18

Aha just found something in the definition list i have about translational kinetic energy: State: "that the mean translational kinetic energy of an atom of an ideal gas is directly proportional to the temperature of the gas in kelvin;
E = 3/2kT KE = 1/2mv2
3/2kT = 1/2mv2 (3/2k is a constant)
T is proportional to KE
Hope that helps :smile:

Reply 393

Shack93

6

Original post by Stevo F

Just quickly skimmed through it, not sure this would get you the mark cause in the mark scheme of the last paper i did it said that inter-molecular forces included forces when particles collide, whether that be right or wrong.

You need to say other than during a collision

Reply 394

Ralphus J

Sorry if this has already been brought up, what do we need to know about mean squared speed? Do we have to know how to derive it? :s-smilie:

Reply 395

Jetblast

9

Original post by Beresford George

Yeah thats right :smile:

Sometimes you also have to talk about their being no kinetic energy due to the velocity of the object being 0, when at absolute 0. However there is minimum potential energy (electrical) meaning that there is still energy inside the object, however no more energy can be taken from the object. (hence absolute zero)