paper 3 Flashcards
how has the atomic model changed overtime?
- dalton: small indestructible spheres, all atoms in an element are the same, atoms in one elemnt are different from another
- JJ. Thompson: discovery of negativley charged eletcron in all atoms, plum pudding model, over neutral
- Rutherford: tiny positivley charged nucleus (mass concentrated) , electrons round the outside
- Bohr: electrons can only move in fixed orbits (shells)
why do models change?
new evidnce brought up that cannot be explained using new models/ideas
describe the atom
- positivley charged nucleus
- surrounded by negativley charged electrons
- all mass in nucleus
- nuclear radius smaller than atom
what is the typical size of atoms and small moleucles
1 × 10^–10m
define density
how much mass is contined within a certain volume
what are the differences in density between a solid liquid and gas?
- in 1cm^3 there are more particles in a solid then in 1cm^3 of a gas
describe how mass is conserved when substances
melt, freeze, evaporate, condense or sublimate
- The law of conservation of mass states that you have to add or remove material for the mass of the system to change
how do physical changes differ from chemical changes?
- physical changes: particles are simply re-arranged and can recover it’s orginal properties if the change is reversed
- chemical changes are not easily irreversible
what are the effects of heating a system?
- energy stored within the system will increase, increase in temperature
- produce a change of state
- make chemical reactions happen
define the term specific heat capacity
the amount of energy needed to raise 1kg of a substance by 1kelvin
the lower the S.H.C the more easily it heats up
define specific latent heat of fusion
- the energy required to transfer 1kg of a substance from the solid state to the liquid state
(melting)
define specific latent heat of vaporisation
- the energy required to heat 1kg of a substance from liquid state to the gas state
(evaporation)
define temeperature
- the measure of the average kinetic energy of particles
how does the motion of a molecule of gas relate to the pressure?
- the more particles collide with the inside of the balloon (surface of container)
- producing a force with each collision, making an overall larger force
- exerted upon a certain area, gives rise to a pressure
how does the temperature of a gas relate to the pressure?
at constant volume
- more temperature
- particles have on average more kinetic energy
- collide more frequently with the walls of the container
- collsions produce a larger force over a given area
- producing a larger pressure
what is extrapolation?
extending the line of a graph, to estimate what would happen if you continue to change the independant variable
what happens when gases are compressed or stretched?
- the collsions of the gas particles produce a net force at right angles to any surface
what happens to the pressure of a gas when the volume is halved ?
at constant temperature
behaviour regarding particle
velocity and collisions
* double the number of collisions per second betwen the gas particles and container
* pressure doubles
how can doing work on a gas increase it’s temperature?
- energy transfered to the particles
- gain kinetic energy
- increase in their average energy, increase in energy
describe the earth’s atmosphere
an assumption of uniform
density
explain why atmospheric pressure
varies with height above the surface
of the planet
- atmospheric pressure decreases the higher you travel,
- as there are fewer gas particles
- becuase of a weaker gravitational field
why does a weather ballon expand as it rises?
appliccation Q
- travling higher mrans waker gravitational field
- so there will be less gas particles and a lower atomspheric pressure
- since there is a net outwards pressure (ballon pressure> atmospheric)
- the balloon expands
describe the force of upthrust
- there is a pressure differnce
- more presure is exerted at the bottom of the body, that at the top of the body
- net force upwards
what determines if a body sinks?
- if the weight force of the body is larger than the upthrust force (larger than the weight of the fluid displaced)
what determines if a body floats?
- if weight force = upthrust force
*
describe liquid pressure:
- acts in all directions
why does liquid pressure increase with depth?
- as there is a larger depth in the liquid,
- the molecules exeprience a larger mass force of molecules above
- become more compressed
- pressure is larger
what happens to pressure of liquid with varing densities?
- more dense, means a larger mass of liquid pushing down
- so more pressure
what is the gravitational field strength?
10N/kg
What is the density formula?
Density = mass➗volume
Kg/m 3 =kg ➗m3
How do you measure the volume of an irregular object?
Fill the eureka can to the top
Place object in
Make sure the spout is n a measuring beaker
The amount on the beaker is the volume
What is the specific heat capacity equation?
E = m ✖️S.H.C✖️temperature change(ø)
J= kg ✖️J/kgk ✖️K / °c
In the S.H.C practical, how could you have it more accurate/efficient?
Put a lid on
Use an insulating container
Add conducting gel between object and container
Submerge the heater fully
What is the specific latent heat equation?
Energy = mass ✖️S.LH(v/f)
J= kg ✖️j/kg
E=ML
what is the atmospheric pressure on earth?
100 kilo pascals
100,000 pascals
what is the relationship between the pressure and volume of a gas?
pressure and volume are inversely proportional as long as temperature is held constant.
on a graph the line would have a curved L but wouldn’t tough the axis of the graph
What is the equation for two variables of pressure and volume?
P1✖️V1= P2✖️V2
The product of pressure and volume stays the same before and after a change
What is the liquid pressure equation?
Ro GH
Pressure= density ✖️depth✖️gravitational field (10N/m)
Describe up thrust
A force that occurs whenever a body is immersed within a fluid.
Because of a pressure difference between the top and bottom fluid
What is archimedes principle?
The upthrust experienced by a body is equal to the weight of the fluid displaced
What is the formula for upthrust?
*upthrust is the weight of liquid displaced
Force = ro g h a
Force = density ✖️gravitational field strength ✖️height✖️surface area
Upthrust = ρghA
When will a body float, sink and rise
Float:
mg= ρghA
Rise :
Mg<ρghA
Sink:
Mg> ρghA
how do you measure time and distance?
- time: stopwatch(accuracy and precision) , light gates
- distance: trundel wheel, ruler, ultrasound
what are the differences between scalar and vector quanitites?
- scalar: only magnitude (distance, speed)
- vector: magnitude and direction (displacment, velocity)
what does uniform mean?
eg: uniform acceleration
- occurs at a constant rate
what are the two ways within which bodies interact?
- non contact: fields - rmagnetic fields, electrostatic field, gravitational fields
- contact: when solid forces exert a point on each other
how would to draw with arrows contact and non- contact forces?
non contact : from the centre of the body
conact: from point of contact
describe friction and the normal conatct force:
- friction : when atoms that make up the surface collide when rough surfaces slide over each other
- eg: box sliding on the surface, force of box on surface, force of surface on box
- normal conatct force: solids deform slightly when a force is exerted upon them
- eg: force of elephant on ground and ground on elephant
what is netwon’s 1st law?
- a body will remian stationary or at constant velocity, unless acted upon by a resulatnt force
what is inertia?
a measure of how difficut it is to change the velocity of an object
what is the ‘inertial mass’?
the same thing as normal mass
M=F/A
what happens when the resultant force is not zer0?
- velocity can change
- direction can change
- both
what is the law of conservation of momentum?
the total momentumn before an event is = to the total momentumn after an event
what is an elastic and inelastic collsion?
- elastic: no energy transferred to other stores
- inelastic: enrgy transfered to ther stores
what is power?
the rate of energy transfer
how can an object moving a constant speed be accelerating?
- object is moving in a circle
- direction is constantly changing
- an accelerattion is a vector quanity
what is netwon’s third law?
when two object intract they both exxert a forc upon each other:
* same magntityde
* opposite direction
what are the effects of appyling more than one force to a body?
object can become
* stretched
* compressed
* bent
what is the difference between an elastic and a plastic deformation?
- elastic: after the deforming force is removed, does return to it’s original shape
- plastic: doesn’t return to orginal shape once the deforming force is removed
what is hooke’s law?
the force applied and the extention of a body are dirctly proprtional, until the limit of proportionality has been exceeded
what is the difference between linear and non linear relationships on a force extension graph?
- linear: obeys hooke’s law?
how do you calulate the work done of stretching?
the area under a force extnsion graph
how is weight measured?
scales or newton meter
what is the acceleration in free fall?
10m/2^2
what is the definition of weight?
the force of the earth on an object
what does the gravitational force of an object depend on?
- the distance betwen
- mass of the two
what is the formula for weight?
weight = mass* 10
which forces cause rotation?
force around a pivot point
what differnce does th location of the pivot point make?
the closer the force is to the turning point, the harder it is to produce a turning effect
define the moment of a force
measure of turning effect about a pivot
moment(Nm) = force(N) * distance(m)
is a vector quanity so must state if is clockwise or anti clockwise
what does the moment depend on?
- the size of the force
- the disance from pivot to point, that is 90 to the force
what is the principle of moments?
the anti-clockwise moments are equal to the clockwise moments about a pivot
how do levers transmit the
rotational effects of forces?
- trasmits forces by rotating about a pivot
- level is a force multiplier
how do you calculate the mechanical advantage for a lever?
load/effort
will awlays be more than 1
how do gears transmit forces?
- larger cog exerts a larger force, but only travels half the distance
- ratio of diameters is the ratios of load and effort
in what direction do liquids produce a force?
- pressure produces a force 90 degrees to the surface
how do hydraulics work?
- uses liquids to transmit a force
- two pistons connected by a pipe
- when you push on piston, the pressure is transmitted through the liquid and the other piston moves
- small area and small force
- can lead to a large force over a large area
What is the equation of newton’s 2nd Law
F= M A
N= kg m/s**2
What is acceleration?
The rate of change of velocity.
If direction or speed changes so does acceleration
V - U
———
T
Why is a body moving in a circle at constant speed have a resultant force?
It’s changing direction and therefore velocity, constantly accelerating which means (N’s 1st law) there is a resultant force.
This resultant force is known as centripetal force
What is terminal velocity?
Constant velocity , zero resultant force
Describe a parachuter’s journey
- Weight acts down, no a lot of drag, RF increases down, acceleration, increasing velocity
- Air resistance increases to the point where RF is zero, terminal velocity - no acceleration & constant velocity
- Remains until parachute is opened, SA increases, increasing drag. RF is acting upwards, decreasing velocity
- As velocity decrease so does drag so eventually the RF becomes zero again, terminal velocity 2, contact velocity, zero acceleration
Define momentum
How difficult it is to stop a moving body. The two factors affecting this are mass and velocities.
(A vector value)
How do you calculate momentum? 🅿️
Mass * velocity = momentum
Kg * m/s = kg m/s
How do you apply the LofM when two stationary bodies push and move away from each other?
Eg (explosion)
The total momentum before and after must equal zero , as they were stationary.
To calculate a total:
. Calculate the first object using P = mv
. Then calculate the second object by knowing the fact the Momentum is negative, to equal zero, as they were going in opposite directions
How do you use the L of C when two bodies collide and move off together?
Calculate the total before , by calculating each separate component’s momentum and adding them together.
Calculate the total after but appreciate it as one value , use the momentum of previous to find out other variables
What is work?
The transfer of energy .
Whenever a force acts upon an object, work is done
What is the work equation?
Work done = force * distance
J = N *m
What happens in term of energy when work is done?
Energy is transferred from one form to another.
Eg : kinetic to gravitational potential energy,
When a body is lifted
What is the power equation?
P = E/T
W= J / s
How do you calculate the gravitational force?
Gravitational force = mass * gravitational field strength
N = kg * (N/ kg)
The gravitational field strength is always 10 N/kg on earth
What is the kinetic energy formula?
Kinetic energy = 0.5 ✖️mass ✖️ (speed2)
J =. Kg* (m/s)2
E= 1/2 mc squared
What is the potential energy formula?
Potential energy = mass * height * gravitational field strength
J = kg * m * (N / kg)
U=mgh
What is the equation for Hooke’s Law
Force exerted by spring = K✖️extension
N = (N/m) ✖️m
How do you find the extension?
New length - original length
What does a diagonal line show on a Force Extension Graph?
That it obeys Hooke’s law
What is formula for moment’s?
M= d ✖️force
d is the perpendicular distance from the pivot to the the line of action of force (m)
