PHYSICS
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- Created by: vickieboadi
- Created on: 04-02-18 20:24
equation for density
Density = mass/volume
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Density measured in...
kg/m3 or g/cm3 , 1m3 = 10000cm3
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How do you measure the density of a regular object?
use an electronic balance to find the mass of the object then measure the side of the object and calculate the volume
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equation for the volume of a cuboid
height x length x width
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equation for the volume of a cylinder
πr2 x height
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How do you measure the density of a irregular object? using displacement can
use an electronic balance to find the mass, then fill a displacement can with water util is overflowing. after carefully lower the object into the can collect the water in a measuring cylinder volume of cylinder = volume of object
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Solid
in a solid the particles vibrate about a fixed positions within a close packed regular structure. the particles cannot move in between each other which results solid having a definite shape and fixed volume. solids have a high density.
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Liquids
when a solid is heated it may melt to form a liquid. a liquid does not have a definite shape but a fixed volume, it has quite a high density because the particles are close together density decreases as you heat it up because particles spread out.
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Gases
in a gas the particles move in between each other and are further apart than a liquid, gases take up the shape and volume of its container, gases have a low density because the particles are spread far apart, it decreases as it heats up
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what is internal energy?
energy that is stored inside a system by the particles that make up the system.
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how is internal energy measured?
it is the total kinetic and potential energy of all particles that make up a system
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what doe s heating do to internal energy?
it changes the energy stored within the system by increasing the energy of the particles that make up the system. this either raises the temperature of the system or produces a change of state
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how do we reduce unwanted energy?
through lubrication and the use of thermal insulation. the higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material
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thermal radiation
all warm objects emit infra red radiation, the hotter the object is the more infra red it will radiate, dark matt surfaces are good emitters of infra red they will cool down quicker, light shiny surfaces are bad emitters of radiation,
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thermal radiation
dark matt surfaces are goo absorbers of infra red, light, shiny surfaces reflect the infra red red, the black can will heat up more quickly.
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examples of infra red radiation
in hot weather we prefer to wear light colored clothing, as black clothes make us heat up in the sun. thermos flask has a light shiny surface. this helps keep the drink warm by reflecting infrared rays back into the drink
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conduction
thermal energy always travels from hotter objects to colder ones, in solids the particles are very close together. when they heat up they vibrate more vigorously, these vibrating particles collide with the particles next to them and make them move.
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examples of conduction
each rod has wax at the end. when they are heated equally, the wax in the copper rod melts first, copper is a very good thermal conductors.gases are very good insulators as the particles are far apart.
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why are metals good conductors
metals are particularly good conductors of thermal energy because they contain free electrons that are not bound tightly to the atoms. these electrons move through the metal. plastic and wood are poor conductors but good insulators.
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examples of conduction
Fiberglass insulation helps to keep a house warm, by reducing the heat lost from the roof. saucepans, the hand;e is made from an insulating material, wood or plastic,the pan is made from a conducting material. thermal energy travels through by con
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convection
the particles in liquids and gases are free to move and so can carry thermal energy from one place to another. this is called convection. convection cannot occur in solid because particles cannot move
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how does it work: when a busen burner heats up water in a beaker
the water near the bunsen burner heats up so becomes less dense. it rises and cooler, more dense, water sinks to take its place. the resulting circulation called a convection current
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examples of convection
kettels-; the heating element is at the bottom. the water near it heats up and rises and colder water sinks to take its place. all the water in kettle get warmer. also keeping house warm- reduces heat loss through fibre glass
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equation for change in thermal energy
mass x specific heat capacity x temperature change
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change in thermal energy: measured in...
J/Kg ℃
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what is the specific heat capacity of a substance
is the amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius
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when an object is heated, what does the change in its temperature depend on?
1.the greater the mass of an object, the greater energy needed to heat it up.2.the material of the object 3.the amount of temperature change
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equation for change in temperature:
ΔE=m c Δθ
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what is change in temperature measured in?
in joules (J)
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what is latent heat?
it is the energy needed to change state . when a change of state occurs, the energy supplied changes the energy stored (internal energy) but not the temperature
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what is specific latent heat?
is the amount of energy required to change the state of one kilogram of the substance with no change in temperature
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equation for change in state:
E=mL (mass x specific latent heat)
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what is specific latent heat of fusion
it is the change of state from solid to liquid
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what is specific latent heat of vaporization?
change of state from liquid to vapor
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change of state:
solid->liquid:melting, liquid->solid: freezing, liquid ->gas: boiling, gas->liquid condensation, solid->gas: sublimation
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what happens to a solid in melting or fusion?
solids have strong forces of attraction which hold the particles in a rigid structure, when a solid is heated, the particles gain energy and vibrate more, eventually enough energy is added to allow the particles to break away from each other.
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what happens to a solid in melting or fusion?
energy is needed to break from the forces of attraction, the temperature of the material does not rise although energy is added, this is called latent heat of fusion.
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what happens in evaporation?
when a liquid is heated the particles gain more energy and move more,some of the particles gain enough energy to break away from the surface of the liquid. they have evaporated. energy allows the particles to break away from the liquid, vaporization
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particle motion in gases
the molecules of a gas are in constant random motion. The temperature of the gas is related to the average kinetic energy of the molecules. changing the temperature of a gas, held at constant volume, changes the pressure exerted by the gas.
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pressure in gases
a gas can be compressed or expanded by pressure change. the pressure produces a net force at right angles to the wall of the gas.
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equation for change in pressure of a gas or the volume change:
pV = constant p (pressure)= pascals (Pa) V (volume) meters cubes (m3)
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particle motion gases:
the particles are constantly moving. their motion is completely random this motion can be demonstrated by observing smoke particles, the temperature of a gas is directly related to the average kinetic energy of the particles.
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equation for kinetic energy:
1/2 m x v2 , so the hotter the gas the faster the particles move
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the particle theory of gas explains gas pressure in the following way
1.gas molecules in constant random motion.2 when molecules collide with a surface it exerts on the surface as it changes direction.
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the particle theory of gas explains gas pressure in the following way
3. the pressure exerted by the gas is equal to the total force exerted by the molecule over an area of the surface ÷ by area 4. the net force, and therefore the pressure is at right angles to the surface
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gas pressure and volume:
increasing the volume of a container that the gas is in, means the gas particles collide with the sides of the container less often and the pressure is lower.
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gas pressure and temperature
if a gas is heated up in a fixed volume the pressure will increase. when the gas particles get hotter, they move faster, this means they collide with the walls of the container more frequently so the pressure increases.
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summary of volume temperature and gas pressure
fixed volume- increasing the temperature increases the pressure, fixed pressure- decreasing the volume increasing the temperature, fixed temperature- decreasing the volume increases the pressure
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what is work done....
is when energy is transferred by a force, doing work on a gas increases the internal energy of the gas and can cause an increase in the temperature of the gas
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equation for work done.
force x distance moved in the direction of the force
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Other cards in this set
Card 2
Front
Density measured in...
Back
kg/m3 or g/cm3 , 1m3 = 10000cm3
Card 3
Front
How do you measure the density of a regular object?
Back
Card 4
Front
equation for the volume of a cuboid
Back
Card 5
Front
equation for the volume of a cylinder
Back
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