Physics Unit 2 Flashcards
(218 cards)
0
Q
What are the 3 advantages of nuclear fusion?
A
More energy than fission
Doesn’t leave behind a lot of waste
Lots of hydrogen to use as fuel
1
Q
What are fission fragments?
A
The parts of a nucleus that have been split in nuclear fission
This is the radioactive waste
2
Q
What is nuclear fusion?
A
The joining of 2 light nuclei to create a larger nucleus and release a large amount of energy
3
Q
What are isotopes?
A
Variants of an element that have the same number of protons and electrons but a different number of neutrons
4
Q
Describe how nuclear fission works
A
A thermal neutron strikes a nucleus of the fissile isotope
The mass number of the isotope goes up by 1 because of the thermal neutron making the nucleus unstable
The instability causes the nucleus to split into 2 fission fragments
The fission fragments shoot off at high speed
A few neutrons also shoot off
One neutron hits another nucleus
This is why the chain reaction occurs
5
Q
What are the 2 most important fissile isotopes?
A
Uranium-235
Plutonium-239
6
Q
Describe the second stage of the life cycle of a star
A
Gravitational energy is transferred to heat and when the temperature gets high enough, hydrogen nuclei fuse together to form helium nuclei and give out massive amounts of heat and light
7
Q
What is nuclear fission?
A
The process of splitting nuclei in order to collect energy and start a chain reaction
8
Q
What is the factor that decides how much energy is released in nuclear fission?
A
How heavy the nucleus is
9
Q
What is a fissile isotope?
A
An isotope that can maintain a nuclear chain reaction
10
Q
Describe the third stage of the life cycle of a star
A
The star enters a long stable period where the heat created by the nuclear fusion provides outward pressure to balance the force of gravity pulling everything inwards
The star maintains its energy output for millions of years due to the massive amount of hydrogen
In this stable period, it is called a main sequence star
11
Q
What are the 3 problems with nuclear fission as an energy source?
A
Disposal of waste is very hard and expensive to do
Cost of power plant and decommissioning is very high and it takes a long time
Risk of a major catastrophe like Chernobyl
12
Q
What are the 3 problems with nuclear fission as an energy source?
A
Disposal of waste is very hard and expensive to do
Cost of power plant and decommissioning is very high and it takes a long time
Risk of major catastrophe
13
Q
What is nuclear potential energy?
A
Energy stored between the bonds holding the subatomic particles in the nucleus together
14
Q
In nuclear power stations, how are some of the neutrons stopped so that the chain reaction does not go out of control?
A
Control rods soak up the neutrons
15
Q
Describe what happens to red giants next
A
It then becomes unstable and ejects its outer layer of dust and gas as a planetary nebula
This leaves behind a hot, dense solid core called a white dwarf that finally cools down to a black dwarf and eventually disappears
16
Q
Describe the fourth stage of the life cycle of a star
A
The hydrogen begins to run out and heavier elements such as iron are made by fusion of helium
The star swells into red giant if it is smaller and a red super giant if it is larger
It becomes red because the surface cools
17
Q
What are the 2 disadvantages of nuclear fusion?
A
Can only happen at very high temperatures
You can’t hold the hydrogen at the high temperatures and pressures required for fusion in an ordinary container (very strong magnetic field is needed)
18
Q
Describe the first stage of the life cycle of a star
A
They initially form from clouds of dust and gas and the force of gravity makes the gas and dust spiral in together to form a protostar
19
Q
What is a thermal neutron?
A
A neutron that moves at the same speed as air particles at room temperature
20
Q
What are the masses of fission fragments in comparison to the original nucleus?
A
One is a third of the mass and the other is 2 thirds of the mass
21
Q
Describe the next stage that occurs in red super giants
A
They start to glow more brightly again as they undergo more fusion and expand and contract several times forming elements as heavy as iron in various nuclear reactions
Eventually, they explode in a supernova forming elements heavier than iron and ejecting them into the universe to form new planets and stars
22
Q
Describe the final stage of red super giants
A
The supernova leaves an extremely dense core known as a neutron star
If this star is big enough, it will become a black hole
23
Q
How do you do calculations for alpha decay?
A
Example:
238 234 4
U –> Th + He
92 90 2
24
What is an alpha particle?
2 protons and 2 neutrons which is the same as a helium nucleus
+2 charge
25
What are the properties of beta radiation?
Quite fast and quite small so they penetrate and ionise moderately
26
How do you calculate the half-life of a sample from an activity / time graph?
Look at the initial activity
Half it
Go across from the "half activity" until you touch the curve
Then go down and the time that you get to is the half-life
27
How do smoke detectors use radiation?
A weak source of alpha radiation is placed in the detector close to 2 electrodes
The source causes ionisation which causes a current between the electrodes
If smoke absorbs the radiation, the current stops and the alarm sounds
28
What is the advantage of using gamma rays to sterilise medical equipment?
The high temperatures of boiling are not needed
29
Describe how radiation causes cancer
All types of radiation enter living cells and ionises or destroys them
This causes mutated cells to divide uncontrollably and cause cancer
30
What are the properties of gamma radiation?
Weakly ionising and a high penetration power
31
Why do we use half-life to measure how quickly the activity drops?
Because the activity never actually reaches zero
32
What is interesting about radioactivity?
It is completely random when radiation is emitted and it isn't affected by any physical conditions like temperature etc.
33
How are the 3 types of radiation deflected by electric and magnetic fields?
Alpha and beta particles are deflected in opposite directions because alpha is positive and beta is negative
Gamma doesn't have a charge so the fields don't affect it
34
How does the number of decays per second change as a radioactive sample gets older?
It decreases
35
What are beta particles?
Simply an electron with virtually no mass and a -1 charge
36
How is sterilisation of food and medical equipment done with radiation?
Gamma rays can be used to kill microbes on food and medical instruments
37
What is half-life?
The average time is takes for the number of nuclei in a radioactive sample to halve
38
How do you do calculations for beta decay?
Example:
14 14 0
C --> N + e
6 7 -1
39
What are the 3 types of radiation?
Alpha particles
Beta particles
Gamma radiation
40
Describe the relative proportions of background radiation
51% radon gas
14% rocks and building materials
12% food
12% medical X-rays
10% cosmic rays
1% nuclear industry
41
How is radiation used for tracers in medicine?
Some isotopes can be injected into the body and their progress can be monitored by an external detector
The injected sample must be beta or gamma so that the radiation passes out of the body and the half-life should be short so that the patient isn't exposed to radiation for too long
42
What happens when beta particles are emitted?
A neutron turns into a proton in the nucleus
43
What does it mean if something is ionising and what affects this?
It is a measure of how much they can bash into atoms and knock electrons off them creating ions
Particles are more ionising if they are larger because they are more likely to hit atoms and ionise them
44
What are the properties of alpha radiation?
Relatively large and heavy and slow moving
Low penetration power and high ionising ability
45
What are isotopes?
Isotopes are variants of atoms that have the same number of protons and electrons but a different number of neutrons
46
What are the 5 safety measures to do with radioactivity?
Use radioactive sources for a short time as possible to keep exposure time down
Use tongs (never allow skin contact with a source)
Hold source at arm's length to keep down the amount of radiation that hits you
Keep source pointing away from you and avoid looking directly at it
For larger operations, use lead aprons, screens etc. as a protective measure because it stops all types of radiation although a lot is needed to stop gamma
47
Which are the most dangerous types of radiation that cause cancer?
Beta and gamma are the most dangerous outside the body because they are the most likely to penetrate the body
Alpha is the most dangerous inside the body because the radiation doesn't penetrate out of the body
48
What are the 5 locations / occupations that give a larger radiation dose?
Underground rocks can cause higher levels at the surface especially if they release radon gas which gets trapped in houses
Nuclear industry workers need to wear protective clothing and face masks to stop them touching or inhaling radioactive material
Radiographers in hospitals wear lead aprons and stand behind lead screens
At high altitudes, you are at higher risk of cancer because of cosmic rays (problem for pilots)
Miners have an increased risk because of the rocks underground that are all around them
49
What is the activity of a radioactive sample measured in?
Bequerels
Counts per minute
Etc.
50
How do you do calculations for gamma radiation?
Nothing changes because gamma rays have no mass or charge
51
How does radiotherapy work?
Gamma rays kill at living cells so they can be used to kill cancerous cells
The rays have to be directed carefully and at just the right dosage to kill the cancer without damaging the normal cells too much
52
What do isotopes tend to do?
They are usually radioactive which means that they decay into other elements and give out radiation
53
Describe how the theory of atoms developed over time
Dalton thought that each element was made of a different type of atom and that atoms couldn't be broken up
100 years later, Thomson discovered that electrons could be removed from atoms and suggested that atoms were spheres of positive charge with tiny negative electrons stuck in them (plum pudding theory)
10 years later, Rutherford and Marsden fired a beam of alpha particles at thin gold foil and expected that the positively charged alpha particles would be deflected by the electrons in the plum pudding model
However, most of the particles went straight through but a few came straight back at them
From this, they suggested the atomic model we use today
54
How do you calculate the half-life of a sample in the exam?
Example:
The activity of a sample has gone from 640 to 80 cpm in 2 hours. Calculate the half life
Initial - 640
After one - 320
After two - 160
After three - 80
So 2 hours is 3 half-lives meaning that a half-life is 40 minutes
55
What are the 4 main uses of radiation?
Smoke detectors
Tracers in medicine
Radiotherapy
Sterilisation of food and medical instruments
56
What are the masses and charges of protons, neutrons and electrons?
Protons have a mass of 1 and a charge of +1
Neutrons have a mass of 1 and no charge (0)
Electrons have a mass of 1/2000 and a charge of -1
57
What does it mean if something has high penetrating power and what affects this?
It can penetrate further through materials
Smaller particles penetrate further because they don't hit as many atoms etc.
58
What are gamma rays?
They are high frequency electromagnetic waves that have no charge or mass
59
How should fuses be rated?
So that their maximum current is slightly higher than the current of the circuit
60
How are earth wires different to the love and neutral wires?
They are thicker and haveess resistance so that a higher current can flow in order to melt the fuse
61
Why are electrical insulators needed?
The human body conducts electricity and this needs to be prevented
62
How do you calculate the frequency of an AC supply using an oscilloscope?
Calculate the time period by looking at the time between 2 consecutive peaks
Calculate the frequency by doing 1 / time period
63
What are circuit breakers?
An electrical safety device that detect surges in current and break the circuit by opening a switch
64
What is the voltage of mains electricity?
230 volts
65
What is difference between AC and DC?
AC can change direction but DC travels in one direction only
66
What is the disadvantage of circuit breakers?
Much more expensive than fuses
67
What is the voltage of the neutral wire?
0 volts even though it carries the electricity back
68
Why do some plugs have a plastic earth pin?
The casing is not conductive meaning the earth wire is not needed
69
Describe how cathode ray oscilloscopes work
If you plug in an AC supply into an oscilloscope, you get a trace on the screen that shows how voltage changes with time
You get a sine wave that goes positive then negative then positive
With a DC supply, you get a straight line
70
How often does mains current alternate?
50 Hz
| 50 times a second
71
What are the 3 advantages of circuit breakers?
Can be reset by flicking a switch where fuses have to be replaced
Break the circuit much faster than fuses
Work for tiny current changes that might not be large enough the melt a fuse
72
What are the colours of the live, neutral and earth wires?
Live is brown
Neutral is blue
Earth is green and yellow
73
How do you calculate the voltage from an oscilloscope?
For an AC supply, the peak of the sine wave is the voltage
For a DC supply, the height of the straight line is the voltage
74
What is double insulation?
When an appliance has a plastic casing and no metal parts showing, it is double insulated
This means that no earth wire is needed because there is no metal casing
75
What are the live, neutral and earth wires for?
The live carries the electricity to the socket of the plug
The neutral completes the circuit
The earth is connected to the casing of the appliance providing a safe route for the current
76
What do we do to prevent electric shocks when a live wire is touching a metal casing?
Attach an earth wire to the metal casing to provide a safe route for the current
77
What is the most commonly used circuit breaker and how does it work?
Residual current circuit breakers
Normally, the same current flows through the live and neutral wires but if someone touches the live wire, the neutral wire will carry back less current than the live wire
The device detects this difference in current and quickly opens a switch
78
What type of electricity do batteries and cells supply?
Direct current
79
On an oscilloscope, what do the gain and timebase dials do?
The gain dial controls how many volts each centimetre division represents on the vertical axis
The timebase dial controls how many milliseconds each division represents on the horizontal axis
80
What are the 9 electrical hazards in the home?
Long cables
Frayed cables
Cables in contact with something hot or wet
Water near sockets
Shoving things into sockets
Damaged plugs
Too many plugs in one socket
Lighting sockets without bulbs in
Appliances without their covers on
81
What makes a material an electrical conductor?
Freely moving charged particles
82
Why does the earth wire from the casing have a low resistance?
If the live wire touches the casing, there would be an increase in current in the live wire which would cause the fuse in the live wire to melt
83
If facing an electric plug, what is each socket? (Live, neutral and earth)
The bottom-right is the live
The bottom-left is the neutral
The top is the earth
84
What happens to voltage in series circuits?
Voltage is shared between the components
The voltage in a component is directly proportional to the resistance
The voltages of cells add up
85
Describe the basic test circuit
The order of the circuit is:
Cell
Variable resistor
Ammeter
Component to be tested with voltmeter in parallel around it
Back to cell
86
What is the symbol for an LDR?
Resistor with circle round it and 2 diagonal arrows pointing at it
87
What is the V/I graph like for a diode?
The current remains at 0 until a certain point where the line goes up at an increasing gradient
This is because the current will only flow through a diode in one direction
The resistance in the opposite direction is very high
88
What is the V/I graph like for different resistors?
A straight line with a positive gradient (gradient varies for different resistors)
The straight line means that the resistance is constant
89
What is the symbol of a battery?
Symbol for a cell then a horizontal dotted line then another cell symbol
90
What is the symbol for a cell?
Horizontal line connecting to long vertical line, then a gap, then a short vertical line connecting to a horizontal line
91
What is voltage?
The amount of energy transferred (joules) per coulomb of charge that passes between two points in a circuit
92
What is the symbol for a diode?
Horizontal line connecting to hollow triangle then a vertical line connecting to horizontal
Whole thing inside circle
93
What is the symbol for a fuse?
Horizontal line goes through a long rectangle
94
Describe thermistors
Temperature dependent resistor
In hot conditions, resistance drops and vice versa
95
What happens to current in a series circuit?
The current is same in all parts of the circuit
96
What happens to the current in a parallel circuit?
Current is shared between branches
The amount of current going down one path is inversely proportional to the total resistance of that path
97
What is the symbol for a resistor?
Horizontal line then long rectangle then horizontal line
98
What is the symbol for a variable resistor?
Resistor with diagonal arrow through it
99
What is the test circuit used for?
You vary the resistance of the variable resistor and look at the voltage and current
You can plot all of the data in a V/I graph and find the resistance of the component
100
What is the symbol for a switch?
Horizontal line to small circle to diagonal line
Then another small circle and a horizontal line
This is an open switch
101
What is the symbol for an LED?
Diode with 2 diagonal arrows coming off it
102
Describe LEDs
Emits light when a current flows through it in the forward direction
Better than filament lamps because they need a smaller current to produce the same light intensity
103
Describe diodes
Made from semi conductor (like silicon)
Used to let current through it in only one direction because there is a high resistance in the other direction
104
What is the symbol for a thermistor?
Start with a resistor
Start a horizontal line below it and quite soon, turn it into a diagonal line that goes through the resistor
105
How do you calculate resistance from a V/I graph?
Use V = IR to calculate the resistance from the current and voltage deltas (draw triangle under line)
The steeper the graph, the lower the resistance
106
Describe LDRs
Resistor that changes resistance depending on light intensity
Bright light gives lower resistance and vice versa
107
What happens to the voltage in a parallel circuit?
It is the same across all components
108
What is the V/I graph like for filament lamps?
The line approaches the x axis with an increasing gradient (curve)
When the line is above the x axis, it has a decreasing gradient
This is because as the temperature increases, the resistance increases
109
Why do resistors have a limit to the current that can pass through?
More current means an increase in temperature which means an increase in resistance which means the current decreases again
This is why the graph for the filament lamp levels off at high currents
110
Why does temperature increase resistance?
When electrical charge flows through a resistor, some electrical energy is transferred to hear energy that makes the resistor hot
The heat energy causes ions in the conductor to vibrate more making it difficult for the charge carrying electrons to get through so the resistance is higher
111
What is a V/I graph?
A graph where voltage (V) is on the x axis and current (I) is on the y axis
It can be used to calculate resistance of the component
112
What is current?
The rate of flow of charge
Charge / time
113
What is the symbol for a lamp?
Circle with an X touching the sides inside it
114
What do electrically charged objects do?
They attract small objects places near them
115
What is electric current?
The flow of electric charge
116
Why is there a current in a circuit?
The positive end of the battery is positively charged and vice versa
The electrons in the negative end are attracted to the positive end because opposite charges attract
This causes the electrons to travel through the circuit to get there
117
What is double insulation?
When the live wire and the metal casing have an insulator between them to ensure the live wire can't touch the casing
118
What is static electricity?
When the electrons cannot continue to move and complete the circuit because there is an insulator, this is called static electricity
119
What are the basic units of charge, voltage, current and power?
Charge is coulombs
Voltage is volts
Current is amps
Power is watts
120
What are conductors?
Materials that allow electrical charges to move easily through them
121
In the electrostatic series, which materials take electrons and which give electrons?
Materials at the top of the list are most likely to give electrons
Materials at the bottom are more likely to take electrons
122
What are the other units for voltage, current and power?
Voltage is joules per coulomb
Current is coulombs per second
Power is joules per second
123
What is electrostatic induction?
When we use a charged object to make neutral objects charged
124
What does friction cause electrons to do?
Some electrons jump from one surface to the other which means one surface is positively charged and one is negatively charged
125
What is the electrostatic series?
A series that shows us which materials give or take electrons because of friction
126
What is weight?
The force of gravity acting on the mass measured in Newtons (N)
127
What is mass?
The amount of matter there is in a body which is measured in grams (g)
128
What does gravitational force cause on a planet?
All things accelerate towards the centre of the planet at the same acceleration
For Earth, acceleration is 10m/s^2
129
How do cars make use of our knowledge of air resistance?
They are made more aerodynamic which means that air flows very easily and smoothly past them minimising air resistance
This allows the "terminal velocity" to be higher because there is less air resistance
130
How do you calculate weight?
Mass * gravitational field strength (10 N/kg)
131
What is terminal velocity?
When the force of gravity and the force of the air resistant of a falling object are equal, the object is travelling at terminal velocity
132
What is the strength of gravity on Earth?
10N per kg in GCSE
133
What 2 factors affect terminal velocity?
If the area of the face going against the air resistance is high then there will be more air resistance
If the mass is higher, then the weight will be higher so more air resistance is needed to reach terminal velocity
134
Why do we reach terminal velocity?
When an object falls, the force of gravity is higher than the force of air resistance (friction) slowing them down so they accelerate but as the speed increases, the air resistance increases and the acceleration slows until the force of gravity and air resistance are equal so the object will travel at a constant velocity
135
Why does a feather have such a low terminal velocity?
It has a very wide surface area
It has a low mass
136
What happens to kinetic energy in elastic collision?
The kinetic energy is completely conserved
137
How are force and momentum linked?
Force is the rate of change in momentum
138
What is the formula for kinetic energy?
1/2 * mass * velocity^2
| 1/2mv^2
139
How do regenerative braking systems work?
Rather than converting the kinetic energy to heat energy in brakes, it puts the motor in reverse
This slows the wheels and the motor acts as an electric generator to convert the kinetic energy into electrical energy which is stored as chemical energy in the battery
140
What happens to momentum in an inelastic collision?
The kinetic energy is dispersed as other types of energy
141
How do we calculate change in momentum?
m(v - u)
| Mass * (Final velocity - Initial velocity)
142
What is the unit of momentum?
Kg m/s
143
Describe the 4 ways that cars prevent injury in car crashes
Crumple zones at the front and back of the car crumple on impact which increases the impact time decreasing the force
Seat belts stretch slightly increasing the time taken for the wearer to stop
Side impact bars are strong metal tubes that direct the kinetic energy of the crash away from the passengers to areas of the car
Air bags slow you down more gradually and prevent you from hitting hard surfaces of the car
144
How do you calculate the rate of change in momentum?
m(v - u) / t
| (Mass * (final velocity - initial velocity)) / time
145
How are force and momentum related?
Force is the rate of change of momentum
146
What is the equation that shows the conservation of momentum?
Resultant momentum before = resultant momentum after
147
When an object hits another object and then stops, where is the momentum?
All of the momentum is in the other object that has been hit
148
What is meant by "momentum is conserved"?
That momentum can't be created or destroyed, it is only passed on
149
What is the formula for momentum?
```
P = mv
Momentum = mass * velocity
```
150
If a mass of 20kg was travelling at 10m/s, what would the momentum be?
200 kg m/s
151
If an object hits another object and they both travel together, where is the momentum?
The momentum is in both objects
| If the masses of the objects were the same, the final velocity would be half the initial velocity
152
Why are car crashes dangerous in terms of momentum and how are cars designed to take this into account?
In a car crash, momentum changes very quickly meaning that the forces in the body are very large (because force is rare of change of momentum)
Cars are designed to slow people down over a longer time when they crash so that the rate of change of momentum is smaller
153
Is momentum a vector or a scalar?
Vector
154
If two objects of the same mass collided at the same velocity, the momentum would be 0kg m/s
Explain how this is possible
Momentum is a vector meaning there is a direction
| In this case, the momentum is 0kg m/s because there is no resultant direction to the momentum
155
What are the 2 types of collision?
Elastic
| Inelastic
156
What is Hooke's Law?
If you apply a force to a spring it will stretch and the extension produced is directly proportion to the force applied
157
How does stretched rubber lose energy?
As heat
158
What is elastic potential energy?
Stored potential energy in any elastic object when it is stretched, twisted or otherwise deformed
159
When is a material said to have elastic properties?
If you apply a force to it by stretching or compressing and then release all force, it will revert to its original shape
160
What is the formula for calculating spring constant?
Spring constant = Force applied / Extension
| k = F / x
161
What is the elastic limit?
How far you can stretch a spring so that when you remove all force, it reverts to its original length
162
What is the formula for calculating energy used on a spring?
Energy = Force * Extension / 2
163
Give 2 things that EPE is directly proportional to
Spring's stiffness
| Square of spring's extension
164
What are the 2 groups of energy?
Stored potential energy
| Energy in use
165
What is the gravitational field strength of Earth?
10 N/kg
166
What is the formula for calculating gravitational potential energy?
Mass * gravitational field strength * height
167
In what way is energy transferred in friction?
Kinetic energy is transferred to heat
168
What is a watt in terms of joules?
Watts = joules per second
169
What happens to gravitational potential energy when an object falls to the ground?
It is converted to kinetic energy
170
Why do falling objects heat up?
The friction between the object and the air (air resistance) generates heat
171
What is friction?
Force that opposes a surface which is moving over another
172
What is power measured in?
Watts
173
What causes kinetic energy to be lost?
Friction causes kinetic energy to be transferred as heat
174
What is the formula for work?
Force * distance
175
What is work measured in?
Joules
176
How is gravitational potential energy put to use in the real world?
In hydro-electric power stations
177
What is the formula for power in terms of electricity?
Power = voltage (potential difference) * current
178
What is the formula for power in terms of energy?
```
Power = Energy / Time
P = E / t
```
179
What is kinetic energy compared to work done?
Kinetic energy transferred is work done so you can put them as equal on 2 sides of an equation
180
What does friction cause?
The work put into moving the object is dissipated as heat
181
If a mass of 5kg is lifted 10 metres above the ground, what is the gravitational potential energy of the object?
5 * 10 * 10
| 500 Joules
182
What are the 2 types of friction?
Air resistance
| Contact friction
183
What is power?
The rate at which work is done
184
What is the law of conservation of energy?
Energy can't be created or destroyed but only transferred into different types of energy
185
What is braking distance?
The distance a vehicle travels after the brakes have been applied
186
What is the thinking distance?
The distance the vehicle travels from when the driver decides to stop to when they put their foot on the brake pedal
187
What are the 4 factors that affect braking distance?
How fast you are going
How good your brakes are
How good the tyres are
How good the grip is
188
What are the parts of stopping distance?
Thinking distance
| Braking distance
189
What is the formula for kinetic energy?
1/2 * mass * velocity squared
190
What causes the braking distance to be larger?
A larger vehicle mass
A larger vehicle speed
Together this means a larger momentum because momentum = mass * velocity
191
Where does the kinetic energy of the vehicle go when it brakes?
Heat in the brake discs
192
What is the reaction time?
The time between deciding to stop and putting a foot on the brake pedal
193
What is the formula for calculating work done or energy transferred?
Work done or energy transferred = force * distance moved in direction of the force
194
What is work done measured in?
Joules
195
What are the 5 factors that affect thinking distance?
Tiredness
Illness
No concentration
Taking alcohol / drugs
How fast you are going (more distance covered in your reaction time)
196
What is stopping distance?
How far the vehicle will travel from when the driver decides to stop to when the vehicle stops
197
How do brakes work in terms of physics?
The brakes increase the friction force meaning the backwards force is larger than the forward so the vehicle slows down
198
What is the formula that calculates force?
F = ma
Force = mass * acceleration
199
What is resultant force?
The net force of all opposing forces
200
What are the 3 rules concerning resultant force (Newton's laws of motion)?
If the resultant force on a stationary object is zero, the object will remain stationary
If the resultant force on a moving object is zero, it carry on moving at the same velocity
If there is a non-zero resultant force, the object will accelerate in the direction of the force
201
What are the 2 types of friction?
Between 2 surfaces in contact
When an object passes through a fluid (air or liquid) which is called drag
202
What is friction?
A force that always acts in the opposite direction to movement
203
What is the rule that explains reaction forces?
When 2 objects interact, the forces they exert on each other are equal and opposite
204
How does increasing speed affect frictional forces?
Increasing speed always increases the opposing friction force
205
How do you calculate acceleration from a velocity / time graph?
Divide change in velocity by change in time to find the acceleration by using a gradient right-angle triangle
206
What is the formula for velocity?
```
V = s / t
Velocity = Displacement / Time
```
207
What is displacement?
Distance in a given direction
208
What is the difference between speed and velocity?
Speed is how fast you travel in any direction (scalar)
| Velocity is how fast you travel in a given direction (vector)
209
What is acceleration?
Rate of change in velocity in m/s^2
210
How does acceleration happen in terms of forces?
Forward force must be greater than the force in the opposite direction
211
How do you calculate weight?
```
W = mg
Weight = mass * force of gravity
```
212
What is the formula for calculating acceleration?
```
a = (v - u) / t
Acceleration = (final velocity - initial velocity) / time
```
213
What is the unit of weight?
Newtons
214
In a velocity / time graph, what is a horizontal line?
Constant velocity
215
What does a straight line sloping upwards in a velocity / time graph mean?
Constant acceleration
216
What is the difference between a scalar and a vector?
A vector is a magnitude in a given direction
| A scalar is a magnitude in any direction
217
What is the formula for calculating speed?
```
S = d / t
Speed = distance / time
```
