CRAMMAMAMAMMAM Flashcards
(90 cards)
1
Q
A
2
Q
Name some scalars
A
distance, speed, time, mass, energy and
temperature
3
Q
What is velocity?
A
speed in a given direction
4
Q
Describe the motion of objects falling in a uniform gravitational field with air/liquid resistance
A
When an object falls, initially it accelerates. The resultant force on the object is very large initially, so it accelerates. As the speed increases, the force of friction acting upon the object increases. Eventually the object falls at a steady speed when the force of friction equals the force of weight acting on it. This is called terminal velocity (when the forces are equal)
5
Q
What is weight?
A
a gravitational force on an object that has mass
6
Q
What is gravitational field strength?
A
force per unit mass
7
Q
What is the effect of gravity on weight and mass?
A
Weight is the effect of a gravitational field on a mass. Mass always stays the same, but weight can change depending on how much gravity is acting upon an object.
8
Q
What do the different line types on a distance time graph mean?
A
- Horizontal line (object is stationary or nor moving or zero speed)
- Diagonal straight line (constant velocity)
- Curving up (Increasing velocity or acceleration)
- Curving down (decreasing velocity or deceleration)
- Diagonal straight line downwards (constant velocity in the opposite direction)
9
Q
What do the different line types on a speed time graph mean?
A
- Horizontal line on time axis (stationary, not moving or zero speed)
- Horizontal line above time axis (constant speed)
- Diagonal straight line (constant acceleration)
- Diagonal straight line downwards (deceleration)
- Curving (the acceleration isn’t constant)
10
Q
What is newton’s first law?
A
An object either remains at rest or continues in a straight line at constant speed unless acted on by a resultant force
- This means that no force is required to maintain constant velocity if no external forces act on the object.
11
Q
What is a force?
A
A push or a pull that acts on an object due to the interaction with another object
12
Q
How do forces affect things?
A
- Changes in speed: forces can cause bodies to speed up or slow down
- Changes in direction: forces can cause bodies to change their direction of travel
- Changes in shape: forces can cause bodies to stretch, compress, or deform
13
Q
What is a resultant force and what does it determine?
A
A resultant force is a single force that describes all of the forces operating on a body. It determines the direction in which the object will move as a result of all of the forces and the magnitude of the final force experienced by the object
14
Q
What is Newton’s second law?
A
The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the object’s mass
- a resultant force may change the velocity of an object by changing its direction of motion or its speed (when F=ma is used)
15
Q
What is circular motion?
A
An object moving with constant speed in a circle, the velocity isn’t constant as its direction is constantly changing
16
Q
What is the centripetal force?
A
The direction of the force is towards the centre
17
Q
What does friction act on?
A
object moving through a liquid and object moving through gas
18
Q
What is a moment?
A
The turning effect of a force about a pivot
19
Q
What’s the formula for moment?
A
M = F × d
(M is moment in newton metres (Nm), F = force in newtons (N), d = perpendicular distance of the force to the pivot in metres (m))
20
Q
How to convert between km/h and m/s?
A
To convert between m/s to km/h multiply by 3.6, to do the opposite divide by 3.6
21
Q
What is acceleration?
A
change in velocity per unit time
22
Q
Describe the motion of objects falling in a uniform gravitational field without air/liquid resistance
A
In the absence of air resistance, all objects falling in a uniform gravitational field, accelerate uniformly, regardless of their mass. On earth this is 9.8m/s^2. So long as air resistance remains insignificant, the speed of a falling object will increase at a steady rate, getting larger the longer it falls for.
23
Q
spring constant definition
A
force per unit extension
24
Q
Centre of gravity definition
A
The point through which the weight of an object acts
25
How to make object stable?
The centre of gravity of a symmetrical object is along the axis of symmetry. The position of the centre of gravity affects the stability of an object. An object is stable when its centre of gravity lies above its base. Toppling occurs when, the vertical line through the centre of gravity falls outside the base of support
26
Principle of conservation of momentum
In a closed system, the total momentum before an event is equal to the total momentum after the event
27
Do stiff springs have high or low spring constant?
high
28
What is the law of conservation of energy?
Energy cannot be created or destroyed but can be transferred between energy sources
29
Energy stored in a ball?
Elastic energy
30
Define unit kWh
energy transferred in one hour at a rate of transfer of 1kW
31
Impulse definition
Force x time for which force acts
32
Energy may be stored as...
kinetic, gravitational potential, chemical, elastic (strain), nuclear, electrostatic and internal (thermal)
33
Advantages of fossil fuels
High energy density readily available during peak demand
34
Disadvantages of fossil fuels
Limited supply, environmental pollution (CO2, SO2), finite resource
35
How fossil fuels are used in power stations?
Coal: In coal-fired power stations, coal is burned in a boiler to produce heat.
Natural Gas: In gas-fired power stations, natural gas is burned directly in a gas turbine.
The heat generated from burning these fuels is used to boil water, creating high-pressure steam. The steam drives turbines connected to electrical generators. Turbines are designed with sets of blades (rotor) mounted on a shaft, which rotates when steam is directed onto them. As steam expands through the turbine, its energy is transferred to the rotor, causing it to spin. The spinning rotor generates electricity through electromagnetic induction in the generator.
36
How nuclear fuels are used in power stations?
Nuclear power stations use controlled nuclear fission reactions with uranium to generate heat.
This heat is used to produce steam indirectly through a heat exchanger.
The steam, similar to fossil fuel stations, drives turbines connected to generators to produce electricity. The operation involves the steam passing through a turbine's fixed blades (stator) onto the rotating blades (rotor), where the expansion of steam energy is converted into rotational motion. The rotational motion of the rotor then drives the electrical generator, producing electricity for consumption.
37
Advantages of nuclear fuels
High energy output, low CO2 emissions
38
Disadvantages of nuclear fuels
Radioactive waste disposal issues, potential for accidents (e.g., Chernobyl, Fukushima).
39
Advantage of solar cells for electrical power
no polluting gases, quiet, low maintenance, can be placed on roofs, cheap to run
40
Disadvantage of solar cells for electrical power
intermittent supply, unattractive, takes up space, uses land, d.c. output
41
Advantages of wind energy
Clean energy source, abundant in suitable locations, renewable resource
42
Disadvantages of wind energy
Visual and noise impacts, intermittent nature of wind
43
Advantages of wave energy
Renewable, predictable in coastal areas with consistent waves, renewable resource
44
Disadvantages of wave energy
Technologically challenging, potential environmental impacts
45
Advantages of tidal energy
Predictable and consistent, minimal greenhouse gas emissions, renewable resource
46
Disadvantages of tidal energy
High infrastructure costs, environmental impacts on marine ecosystems
47
Advantages of geothermal energy
Reliable, low emissions, constant energy source, renewable resource
48
Disadvantages of geothermal energy
Limited to geologically active areas, high upfront costs for exploration and drilling
49
Advantages of hydroelectric energy
Reliable, long operational life, minimal greenhouse gas emissions, renewable resource
50
Disadvantages of hydroelectric energy
Disruption of aquatic ecosystems, potential displacement of communities, limited suitable sites
51
Advantages of biofuels
Renewable, lower emissions compared to fossil fuels
52
Disadvantages of biofuels
Competition with food production, land use issues, varying energy content
53
What happens to pressure in a liquid?
Pressure in a liquid increases with depth because the further down you go, the greater the weight of liquid above.
Pressure at one depth acts equally in all directions.
Pressure depends on the density of the liquid; the denser the liquid, the greater the pressure at any given depth.
54
Pressure in a column of water
In a column of water, the highest pressure would be at the bottom
If a hole is made at the bottom of the column, the water will pour out with a large force
If a hole was made at the top of the column, the water will pour out with a small force
This is because of the difference in pressure in the column caused by the weight of the water
55
What are the main features of liquids?
- Fixed volume
- Acquires shape of container
- Forces of attraction between particles are less strong than between a solid
- Particles can freely move and slide over each other (greater energy)
- Irregular arrangement
- Medium density
- Can’t be compressed
- Slowly diffuse
56
What are the main features of solids?
- Fixed volume
- Fixed shape
- Strong attraction between particles
- Particles can’t move freely but can vibrate (low energy)
- Regular arrangement
- High density
- Can’t be compressed
- Can’t diffuse
- The particles are packed very closely together in a fixed and regular pattern
57
What are the main features of gases?
- Not fixed volume
- Not fixed shape
- No or very weak forces of attraction between particles
- Particles move randomly and are spread out (highest energy)
- Irregular arrangement
- Low density
- Can be compressed
- Diffuse quickly
58
What is evaporation?
Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquid's surface at low temperatures, below the b.p. of the liquid. The larger the surface area and the warmer the liquid surface, the more quickly a liquid can evaporate
59
What is Brownian motion?
Brownian motion is the random movement of particles in a liquid or a gas produced by large numbers of collisions with smaller particles which are often too small to see (the random motion of microscopic particles in a suspension is evidence for the kinetic particle model of matter)
60
How do you convert kelvin to celsius and vice versa?
T (in K) = θ (in °C) + 273 T (in °C) = θ (in K) - 273
61
What is absolute zero?
Temperature at which particles have least kinetic energy. Lowest possible temperature
62
What is thermal expansion?
Thermal expansion is a process where a body expands in either area, volume or shape when heated. When heat energy is supplied to an object, the particles have more kinetic energy and start moving faster. This causes the particles to move further apart and as a result it increases in area, volume or shape. Different states of matter expand different amounts depending on how strong the forces are that hold the particles together. (Molecules don’t expand, the space between them does)
63
How do solids expand?
Expand slightly because the low energy molecules can’t overcome the intermolecular forces of attraction holding them together
64
How do liquids expand?
Expand more than solids because the molecules have enough energy to partially overcome the intermolecular forces of attraction holding them together
65
How do gases expand?
Expand significantly because the high energy molecules have enough energy to completely overcome the intermolecular forces of attraction holding them together
66
How do thermostats use thermal expansion?
Thermostats have a bimetallic strip. This is a strip in which there are two metals, with different coefficients of linear expansion, placed side by side. Therefore, when the strips warm up, one of the metals linearly expand more than the other, causing the bimetallic strip to bend. When it becomes hot enough, the strip bends enough to close the circuit, and the air conditioner turns on, cooling down the room. Once the room has reached the desired temperature, the strip slowly unbends, opening the circuit and turning off the air conditioner. The same mechanism can be used for heaters – when it is warm, the strip bends away from the circuit, and is it grows colder, the strip straightens out until it closes the circuit and the heater can turn on again.
67
What are the consequences of thermal expansion?
- The expansion of solid materials can cause them to buckle if they get too hot. This expansion can be significant enough to cause structural damage to buildings, bridges, and other structures.
- This could include:
- Metal railway tracks
- Road surfaces
- Bridges
- Things that are prone to buckling in this way have gaps built in, this creates space for the expansion to happen without causing damage
68
What is internal energy?
Internal energy is the total energy stored inside a system by the particles that make up the system due to their motion and positions
69
What is the specific heat capacity?
The specific heat capacity is the energy required per unit mass per unit temperature increase (1 kg of the substance by 1°C)
70
What does it mean if a substance has a high heat capacity and low heat capacity?
If a substance has a high specific heat capacity, it heats up and cools down slowly (ie. it takes more energy to change its temperature) ex water
If a substance has a low specific heat capacity, it heats up and cools down quickly (ie. it takes less energy to change its temperature) ex copper
71
What happens during evaporation?
- Evaporation is a change in state of a liquid to a gas
- Evaporation occurs when more energetic molecules moving near the surface of the liquid have enough energy to escape
- The average energy of the liquid is reduced, therefore liquids are cooled down by evaporation
- The process of evaporation can be used to cool things down:
- If an object is in contact with an evaporating liquid, as the liquid cools the solid will cool as well. This process is used in refrigerators and air conditioning units
- It happens;
- At any temperature
- Only from the surface of a liquid
72
What are the three factors that affect evaporation?
Temperature, surface area and air movement
73
How does temperature affect evaporation rate?
Higher temperature leads to a higher rate of evaporation. This is because increased temperature increases the kinetic energy of the molecules in the liquid. Molecules with more energy are more likely to overcome the intermolecular forces holding them in the liquid state and escape the surface
74
How does surface area affect evaporation rate?
Larger surface area leads to a higher rate of evaporation. This is because evaporation only occurs at the surface and a larger surface means more evaporation.
75
How does air movement affect evaporation rate?
Increasing air movement, increases the rate of evaporation. This is because it clears the evaporated molecules from the air and allows more water molecules to escape
76
What are the differences between boiling and evaporation?
- Evaporation can happen at any temperature from the melting point to the boiling point while boiling only happens at the boiling point
- Evaporation is on the surface while boiling happens in the entire body of the liquid
77
What is conduction?
Conduction is when two solids of different temperatures come in contact with one another, thermal energy is transferred from the hotter object to the cooler object
78
Why does thermal conduction not happen in liquids and gases?
Thermal conduction in gases and liquids is bad because for thermal conduction to occur the particles need to be close together so that when they vibrate the vibrations are passed along. This does not happen easily in fluids because in liquids particles are close, but slide past each other and in gases particles are widely spread apart and will not 'nudge' each other. Both types of fluid, liquids and gases, are poor conductors of heat.
79
How does thermal conduction happen in solids?
Thermal conduction happens in solids when a substance is heated and the atoms at the hotter end of the solid will vibrate more than the atoms at the cooler end. As they do so they bump into each other, transferring energy from atom to atom, these collisions transfer internal energy until thermal equilibrium is achieved throughout the substance. This occurs in all solids, metals and non-metals alike
80
When does convection happen?
- Convection is an important method of thermal energy transfer in liquids and gases
- It can’t happen in solids only in fluids (liquids and gases)
- Both temperature rising and falling can create convection currents
- Heat does not rise - it is the hot gases or liquids which rise due to the change in density when they were heated.
81
What is convection?
Convection occurs when particles with more heat energy move and take the place of particles with less heat energy.
82
How does convection happen when a liquid/gas is cooled?
The molecules move together, making the liquid/gas contract. This makes the cold liquid/gas more dense than the surroundings. The cold liquid/gas falls, so that warmer liquid or gas can move into the space created. The warmer liquid or gas gets cooled and also contracts and falls down. The resulting motion is called a convection current
83
What is thermal radiation?
Thermal radiation is infrared radiation and all objects emit this radiation. The hotter an object is, the more thermal radiation it emits. Thermal energy transfer by thermal radiation does not require a medium (only way that heat can travel through a vacuum, why heat reaches us from the Sun)
84
What is thermal equilibrium?
For an object to be at a constant temperature it needs to transfer energy away from the object at the same rate that it receives energy
85
Why does an object warm up?
If the rate at which an object transfers energy away is less than the rate at which it receives energy then the object will heat up
86
What affects thermal radiation?
- The surface colour of the object (black=more radiation)
- The texture of the surface (shiny surfaces=less radiation)
- The surface area of the object (greater surface area=more area for radiation to be emitted from)
87
How does radiation contribute to the Greenhouse effect?
- The temperature of the Earth is affected by factors controlling the balance between incoming radiation and radiation emitted
- The Earth receives the majority of its heat in the form of thermal radiation from the Sun. At the same time, the Earth emits its own thermal radiation, with a slightly longer wavelength than the thermal radiation it receives (the surface temperature of the Earth is significantly smaller than the surface temperature of the Sun)
- Some gases in the atmosphere, such as water vapour, methane, and carbon dioxide (greenhouse gases) absorb and reflect back longer-wavelength infrared radiation from the Earth and prevent it from escaping into space. These gases absorb the radiation and then emit it back to the surface
- The rate of absorption and emission of radiation on Earth contributes to the Greenhouse Effect (This is the natural process that warms the Earth's surface from the Sun
- The Sun's thermal radiation reaches the Earth's atmosphere where: Some radiation is reflected back to space, any radiation not reflected is absorbed and re-radiated by greenhouse gases, the absorbed radiation then warms the atmosphere and the surface of the Earth
88
How are the three types of thermal energy transfer shown in a fire burning wood or coal
Conduction: When the fire is lit, the part of the wood or coal that is in direct contact with the flame heats up. This heat energy is transferred from one particle of the wood or coal to another, moving through the solid via conduction.
Convection: As the wood or coal burns and releases heat, the air surrounding the fire becomes warmer and expands. This warm air is less dense than the cooler air above it, causing it to rise. As the warm air rises, cooler air moves in to replace it, coming into contact with the fire, warming up, and rising in turn. This creates a convection current that helps to spread the heat from the fire throughout the room.
Radiation: The fire emits infrared radiation, which travels out in all directions from the fire. This radiation can travel through the air, allowing it to heat up objects that are not in direct contact with the fire.
89
How are the three types of thermal energy transfer shown in a car radiator?
Conduction: The engine of the car generates heat during operation. This heat is conducted through the engine block and to the coolant fluid that circulates around the engine. The heated coolant then flows into the radiator.
Convection: Inside the radiator, the hot coolant flows through thin tubes which maximize surface area for heat transfer. As the coolant flows, it transfers heat to the cooler air flowing through the radiator fins. This heated air becomes less dense and rises, and cooler air moves in to replace it, creating a convection current that cools the coolant.
Radiation: The radiator is designed to maximize the surface area available for heat dissipation. The heat from the coolant is not only transferred to the air by convection but is also radiated from the surface of the radiator to the surrounding environment.
90
How does an insulator keep something warm?
The insulator contains trapped air, which is a poor conductor of heat, trapping the air also prevents it from transferring heat by convection, this reduces the rate of heat loss from the object, meaning that it will stay warmer for longer
