Topic 9: Matter Flashcards
What’s the equation for Density?
Density = Mass/Volume
What does the average density of an object determine?
It determines whether it floats or sinks
When will an object float on a fluid?
The solid will float on a fluid if it has a lower average density than the fluid
How can you find the density of solids and liquids?
Measure its mass and volume and use the formula
What’s a closed system?
A system where no particles can get in and none can escape
What happens to the mass of a substance when it changes state? - why?
It stays the same because the particles are just being rearranged, not changing
What happens to the volume of a substance when it changes state? - why?
The volume changes because in solids the particles are usually closer together than in liquids (except for ice and water)
What happens to the density of a substance when it changes state? - why?
Changes, because the volume changes and density = mass/volume
What’s the specific heat capacity?
The change in energy in a substance’s thermal energy store to raise the temperature of 1kg of that substance by 1 degrees C
How do you find the specific heat capacity of water?
- Measure the mass of an insulating container (using a mass balance), then measure the mass again with water in it, difference in mass is the mass of the water
- Place a thermometer and immersion heater into the water and read the starting temperature (put a lid on)
- Connect a joulemeter to the immersion heater and make sure it reads 0
- When the temperature has reached e.g. 10 degrees, stop the experiment and record the energy on the joulemeter and the increase in temperature
- Plug in the values to the rearranged equation
- Repeat experiment 3 times and calculate the average specific heat capacity
Why may the specific heat capacity core practical not be fully accurate?
- Thermal energy may be passing out of the beaker, into the air (so, use an insulator with a lower thermal conductivity)
- Not all the thermal energy from the immersion heater may be passing into the water (so, make sure the heater is fully submerged)
- Incorrect reading of thermometer (so, use an electronic temperature probe instead)
What happens in terms of energy when you heat a solid or liquid?
The energy is transferred to the kinetic energy stores in the particles of the substance, so the particles vibrate and move faster
What happens in terms of energy when a substance is condensing or freezing?
Bonds are forming between particles, which releases energy so the temperature doesn’t go down until all the substance has turned to liquid or a solid
What’s specific latent heat?
The amount of energy needed to change 1kg of a substance from one state to another without changing its temperature
What is the specific latent heat for melting and freezing (changing between a solid and liquid) called?
Specific latent heat of fusion
What is the specific latent heat for evaporating, boiling and condensing (changing between a liquid and a gas) called?
Specific latent heat of vaporisation
According to kinetic theory, what is all matter made up of?
Very small, constantly moving particles
What happens to gas particles in a sealed container?
The gas particles collide with each other, when they collide with something, they exert a force (an so a pressure)
What happens to gas particles in a sealed container at high temperatures?
- The higher the temperature, the more kinetic energy the particles have, so they move faster
- The faster they move, the more often they can collide with each other and the container
- The collisions have a higher energy at higher temperatures, also
- So, increasing the temperature of a fixed volume of gas increases its pressure
What’s the relationship between pressure and volume?
They are inversely proportional
What temperature is the coldest you can get (absolute zero)
-273 degrees C
- 0 kelvin
How do you convert from Celsius to Kelvins?
Add 273
How do you convert from Kelvins to Celsius?
Subtract 273
When is the volume of a container constant?
For containers without a fixed volume, the volume of the container is constant 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 volume of a gas in a container without a fixed volume?
By changing either the internal (pushing outward) or external (pushing inward) pressure on the container
How can you change the pressure of a gas inside a container?
- Heating/Cooling
- HEATING: As gas particles inside gain energy, they move around faster which increases the pressure. So, the outward pressure of the gas inside the (e.g. balloon) is now larger than the inward pressure caused by the surroundings. The (e.g. balloon) volume of the gas expands until the pressures are equal again
- COOLING: Gas in the balloon has the opposite effect (outward pressure is smaller than the inward pressure, so the gas inside the balloon is compressed)
What is ‘work’?
The transfer of energy by a force
How does doing work on a gas increase its temperature/why does pumping up a bike tyre increase its temperature?
- Gas exerts pressure on the plunger of the pump, so it exerts a force
- Work has to be done against this force in order to push down the plunger
- This transfers energy to the kinetic energy stores of the gas particles which increases the internal energy and therefore the temperature
- If the pump is connected to a tyre (for example), some of this energy is transferred from the gas to the thermal energy store of the tyre, and you’ll feel the tyre getting warmer
What does ‘inelastically distorted’ mean?
An object that doesn’t return to its original state and length after the force has been removed
What’s the elastic limit?
The point where an object stops distorting elastically and begins to distort inelastically
When is work done on a compressing object?
Work is done when a force stretches or compresses an object causing energy to be transferred to the elastic potential energy store of the object
What happens, in terms of energy, when an object is elastically distorted?
When elastically distorted, all this energy is transferred to the object’s elastic potential energy store
What’s the relationship between extension and force?
Extension is directly proportional to force (linear)
What’s the limit of proportionality?
The point on the graph where the relationship is no longer proportional - maximum force is achieved
If the spring is stiff, how is the spring constant?
Greater
What’s the elastic limit?
The point on the graph where the object is permanently stretched, so it levels off
What’s pressure?
The force per unit area
What’s the equation for pressure in solids, liquids and gases?
Pressure (pascals - Pa) = Force normal to surface (N) / Area of that surface (m squared)
What’s fluid pressure caused by?
Fluid pressure is caused by the collisions of gas or liquid particles on a given surface.
Fluid pressure always exerts force at right angles to any surface in contact with the fluid
What does fluid pressure depend on?
Depth and density
In which states of matter is density uniform and not uniform?
Liquid - uniform
Gas - non uniform
Why does fluid pressure increase with density?
A denser fluid has more particles in a certain space than a less dense one
So, there are more particles that can collide so the pressure is higher at a given depth in the denser fluid
Why does fluid pressure increase with depth?
As the depth of a fluid increases, the number of particles above that point increases
So, the weight of these particles adds to the pressure felt at that point, hence, fluid pressure increases with depth
Why do objects in fluids experience upthrust?
- When an object is submerged in a fluid, the pressure of the fluid exerts a force on it from every direction
- As pressure increases with depth, the force exerted on the bottom of the object will be greater than the force acting on the top of the object
- This causes a resultant force, known as upthrust (which is equal to the weight of the fluid that has been displaced by the object)
In what conditions will an object float?
When the upthrust equals the weight of the object, the forces balance and the object floats
What’s the atmosphere?
A layer of air that surrounds Earth
How does altitude relate to atmospheric pressure?
As altitude increases, atmospheric pressure decreases
This is because as the altitude increases, the atmosphere gets less dense, so there are fewer air molecules that are able to collide with the surface
State why the total pressure on a diver going deeper in water is greater than just the pressure due to the water above the diver.
There is additional pressure due to the atmosphere
State two factors that affect the pressure of the atmosphere on the aeroplane as the aeroplane goes higher in the atmosphere.
- Height of atmosphere (above the plane)
- Temperature of atmosphere
- Density of atmosphere
When objects are submerged in water, what does the displaced water show?
- Upthrust is equal to water displaced
- This upthrust/water displaced is equal to the weight of the object
- More water has to be displaced to provide more upthrust when the object is heavier
