Section 7 - Matter Flashcards
What is density?
Mass per unit volume
What is the density equation?
p = m / V Density = Mass / Volume
What does density determine?
Whether an object can floatr
What must the density of a solid object to float be?
Lower average density than the fluid
How do you find the density of a substance?
Weight its mass and measures its volume
How can you find the mass and volume of a liquid?
Add into a measure cylinder and weigh and find volume
How can you find volume of prism or cube?
Calculate volume (maths)
How can you find the density of an object which isn’t a regular shape?
Add water in to a density bottle and find the volume of water before and after adding the object
Then plug the change of volume into density
An object has a mass of 0.45kg and a volume of 75cm^3
Calculate its density in kg/m^3
75cm^3 = 7.5e-5
P = m / V P = 0.45 / 7.5e-5 P = 6000 kg/m^3`
What is the difference between a physical change and a chemical change?
In a physical change the only the FORM of a substance changes where as in a chemical change new substances are CREATED by the reaction
Where is the thermal energy in a substance held?
In the particles kinetic energy store
What is boiling?
The particles having enough energy to break the bonds/forces causing the gas to form as bubbles
What happens to the mass of a physical change?
Remains the same (if a closed system)
Whats happens to the volume of a physical change?
Changes
Why does density change during physical changes?
Because, although, the mass remains constant (providing the system is closed) as the forces get weaker/stronger the volume will get larger/smaller causing a changing density
Generally, when are substances most dense?
When they’re solid
What is the specific heat capacity?
The change in energy in the substance’s thermal store needed to raise the temperature of 1kg of that substance by 1*C
WHat is the specific heat capacity equation?
Thermal Energy Change = Mass x SHC x Temperature Change
When finding the specific heat capacity of water, why is insulation used?
To reduce energy wasted to the surroundings
How do you find the specific heat capacity of water?
Find the mass of the water
Measure the temp, and then turn on the power
Stop the experiment after an increase in temperature, and record the energy on the joulemeter and the increase in temperature
How do you calculate specific heat capacity?
Specific Heat Capcity = Change in thermal energy / (Mass x Temperature change)
Why is energy needed during physical changes?
Ti break the intermolecular bonds
What happens when a substance is melting or boiling to the energy?
The energy used for breaking intermolecular bonds rather than raising the temperature
How can you get a graph for physical changes?
Fill a beaker with ice Place a thermometer in the beaker and record the temperature of the ice Heat the beaker full of ice Record the temp every 20 seconds Plot a graph
What is the definiton of specific latent heat?
The amount of energy needed to change 1 kg of a substance from one state to another without changing its temperature
Whats the specific latent heat equation?
Specific Latent Heat = Thermal Energy / Mass
What creates pressure?
Colliding gas particles
What is most gas made up of
Empty space
What is the pressure of a sealed container?
The total force exerted by all of the particles in the gas on a unit area
What does gas pressure depend on?
Temperature and volume
Why does temperature increase gas pressure?
Because heating the gas will make the particles faster meaning they will collide more often therefore increasing the pressure of the gas
What happens when to the pressure as increase the volume of a gas
The pressure decreases
Why does an increase in gas volume decrease gas pressure?
Because increasing the gas volume means the particles get more spread out and hit the walls of the container less often meaning the pressure decreases
What is the relationship between pressure and volume
Inversely proportional
What is the equation linking pressure and volume?
V1xP1 = V2xP2
What happens as you increase the temp of an object?
The particles move more
What is absolute zero?
The point of lowest kinetic store
Find the value of 25 *C in kelvin?
25 + 273 = 298 K
Explain how a gas exerts pressure on its container?
When gas particles collide with the walls of their container, they exert a force on it
3.5 m^3 of a gas is at a pressure of 520 Pa. It is compressed to a volume of 1 m^3 at a constant temperature
What is the new pressure of the gas?
P1 x V1 = P2 x V2
3.5 x 520 = P2
1820 = P2
What does a change in pressure cause?
A change in volume
What directions do the pressure collisions occur?
Random
When you add the pressure angles together what do you get?
Right angles to the wall of the container
When does the outside of a container not get under double pressure?
When its a vacuum
When does the volume of an container not change?
When the pressure of the gas inside pushing outwards is equal to the pressure of the air outside pushing inwards
How can you change the pressure of a gas inside a container?
By changing temperature (heating or cooling)
What happens to a balloon (container) when it is heated?
The gas particles inside it gain energy and move around quicker increasing the pressure of the balloon which leads to an increasing outward pressure which is larger that the inward pressure caused by the surroundings therefore the balloon expands until the pressures are equal
What happens to a balloon (container) when it is cooled?
The gas particles inside it lose energy and move around slower decreasing the pressure of the balloon which leads to an decreasing outward pressure which is smaller that the inward pressure caused by the surroundings therefore the balloon shrinks until the pressures are equal
How does the atmospheric pressure affect the container volume?
As you increase the altitude the inward pressure decreases this causes the gas to expand as the altitude increases
What does doing work on a gas cause?
An increase in it’s internal energy
Explain why pumping a bike tyre increases the tyre’s temperature?
The gas particles in the tyre exert a force on the pump so work is done against this force, this transfers energy to the kinetic energy stores of the gas particles
What happens to an object when you apply a force to it?
It can stretch, compress or bend
For an object to stretch, compress or bend, what must it experience?
MORE than one force
What must more than one force be on an object for it to stretch, compress or bend?
If it was just one force, the object would simply move in the direction of the force
What can happen an object that has been distorted?
It can go back to its original shape and length
What can happen an object that has been distorted?
It can go back to its original shape and length
What are elastic objects?
Objects that can be elastically distorted
What is an object that is inelastically distorted?
An object that doesn’t return to the original shape and length after the force has been removed
What is the elastic limit?
The point where an object stops distorting elastically and begins to distory inelastically
What is done when a force stretches or compresses an object?
Work
What store is energy converted to if an object is elastically distorted?
Elastic potential energy store
What is extension directly proportional to?
Force
What type of relationship is there between force and extension?
Linear
What is the force and extension equation?
F = K x x Force = Spring Constant x Extension N = N/m x m
What is the k in extension?
The spring constant
What unit is the spring constant in?
N/m
How high is a spring constant for a stiff object?
Higher
A stiff object will have a ______ spring constant
A stiff object will have a greater spring constant
When is the extension not ∝to the force?
When the elastic limit is broken
A spring is fixed at one end and a force of 1 N is applied to the other end, causing it to stretch
The spring extends by 2 cm
Calculate the spring constant of the spring?
2 cm = 0.02 m
F = k x d 1 = k x 0.02 k = 1 / 0.02 k = 50 N/m
What is the weight equation?
Weight = Mass x Gravitational Field Strength N = Kg x N / Kg
When investigating elasticity, why is a quick pilot experiment done?
To find out what size masses to use
When investigating elasticity, what is the pilot experiment
Use an indentical spring and load it with masses and plot a graph and check for a straight line, if the curves too early, you need to use smaller masses
When investigating elasticity, when doing a quick pilot experiment what should you see?
A straight line
When investigating elasticity, when doing a quick pilot experiment what shouldn’t you see?
If it curves
When investigating elasticity, what must you first do?
Measure the natural length of the spring
When investigating elasticity, when measuring what must you do?
Make sure you take the reading at eye level and add markers to the top and bottom
When investigating elasticity, what do you do?
Add a mass to the spring and measure the new length
Repeat until atleast 6 points
Plot a graph
When investigating elasticity, what is the extension?
The change in length
When investigating elasticity, what does a larger force cause?
A bigger extension
When investigating elasticity, how do you find work done (from a graph)?
By calculating the area under the linear section of your graph
What is the energy transferred in stretching equation?
E = (k x X²) / 2 Energy = (Spring Constant x Extension²) / 2 J = (N/m x M²) / 2
What does an object with distorion always being elastic mean?
All the energy being transferred is stored in the spring’s elastic potential energy store
When is the work done to the spring equal to the energy in the elastic potential store?
When the spring is not stretched past its limit of proportionality
A spring with a spring constant of 40 N/m extends elastically by 2.5cm
Calculate the amount of energy stored in its elastic potential energy store
E = (k x X²) / 2 E = (40 x 0.025²) / 2 E = 0.0125 J
What is pressure?
The force per unit area
What is the pressure equation?
P = F / A Pressure = Force / Area Pascals = Newtons / Meters²
Which states count as fluids?
Gas and liquids
What are fluids?
Substances where their particles are free to move
Where does fluid pressure always exert a force?
90* to any surface
What does fluid pressure depend on?
Depth and density
What is the density for a liquid?
Fixed
What is the density for a gas?
Forever changing
Assuming the particles are the same mass, which will have a higher pressure?
A more dense or a less dense liquid?
A more dense liquid
Assuming the particles are the same mass, which will have a higher pressure?
A more dense or a less dense liquid?
A more dense liquid
Why does density affect pressure?
Because the more dense the liquid, the more particles that are able to collide meaning the pressure will be higher
How does depth affect fluid pressure?
The deeper the fluid, the higher the pressure
Why does depth affect fluid pressure?
The deeper the fluid, the more particles that are above that point. The weight of these particles add to the pressure
What is fluid pressure equation?
P = h x p x g Pressure = Height (depth) x Density x Gravitational Field Strength Pascals = Meters x Kg/m³ x N/kg
The density of water is 1000 kg/m³
The gravitational field strength of the Earth is 10 N/kg
Calculate the change in pressure between a point 20m below the surface of water and a point 40m below the surface
P = h x p x g
P1 (20m) = 20 x 1000 x 10
P1 (20m) = 200,000 Pa
P2 (40m) = 40 x 1000 x 10
P2 (40m) = 400,000 Pa
P2 - P1 = 400,000 - 200,000 = 200,000 Pa
Can you have negative pressure?
No
Calculate the force exerted on a 10m² area by a pressure of 200kPa
200 kPa = 200,000 Pa
P = F / A F = A x P F = 10 x 200,000 F = 2,000,000 N
At a point 5cm below the surface of a jug of olive oil, the pressure is 450 Pa
Calculate the density of olive oil. The gravitational field strength of Earth is 10 N/kg
5cm = 0.05m
P = h x p x g p = (h x g) / P p = 450 / (10 x 0.05) p = 900 Kg/m
What do objects in fluids experience?
Upthrust
Why do objects experience fluid upthrust?
Because pressure acts on the object, there is a resultant force (upthrust)
What is the upthrust in fluids equal to?
The weight of the fluid that has been displaced
When does an object float?
When
Weight = Upthrust
Why does density affect whether an object floats or not?
When an object that is less dense than a fluid, is placed in that fluid. The volume of fluid that is displaced is equal to its weight before it is completely submerged
How do submarines sink?
They fill large tanks with water
What does atmospheric pressure decrease with?
Height
Why does air pressure decrease with height?
As you get higher, the atmosphere gets less dense so there are fewer air molecules that are able to collide with the surface
Explain a wooden object (p of 700 kg/m³) floats in water (p of 1000 kg/m³)
The wood object is less dense than water which means that when the wooden object is placed in water, it can displace enough water to create an upthrust equal to the weight of the object so the upthrust equals the weight and it floats
Is a change in state physical or chemical?
Physical
Name five changes of state?
Melting Boiling Freezing Condensing Subliming
Define specific heat capacity?
The heat required to raise the temperature of 1kg of a substance by 1*C
Define specific latent heat?
The change of state of a substance is the amount of energy needed to change 1kg of it from one state to another
What is the difference between an elastic and an inelastic distortion?
Elastic distortion is when an object returns to its original shape once the forces are removed
Inelastic distortion is when an object does not return to its original shape it is an inelastic deformation.
In what conditions will an object float?
When an object is less dense than a fluid
