AQA Additional Science. Physics 2. A slideshow that covers the entire AQA 2006 Syllabus Physics 2 Module. W Richards. Distance, Speed and Time. Speed = distance (in metres) time (in seconds). D. S. T. Seb walks 200 metres in 40 seconds. What is his speed?
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Physics 2
A slideshow that covers the entire AQA 2006 Syllabus Physics 2 Module
W Richards
Speed = distance (in metres)
time (in seconds)
D
S
T
This car is travelling at a speed of 20m/s
This car is travelling at a velocity of 20m/s east
Speed is simply how fast you are travelling…
Velocity is “speed in a given direction” (a “vector quantity”)…
VU
Acceleration = change in velocity (in m/s)
(in m/s2) time taken (in s)
A
T
80
60
40
20
0
Velocity
m/s
T/s
10 20 30 40 50
60
40
20
0
Velocity
m/s
T/s
10 20 30 40 50
Reaction
Consider a camel standing on a road. What forces are acting on it?
These two forces would be equal – we say that they are BALANCED. The camel doesn’t move anywhere.
Weight
Reaction
What would happen if we took the road away?
The camel’s weight is no longer balanced by anything, so the camel falls downwards…
Weight
A force is a “push” or a “pull”. Some common examples:
Air resistance/drag – a contact force that acts against anything moving through air or liquid
Weight (mg) – pulls things towards the centre of the Earth
_____ – a contact force that acts against anything moving
Upthrust – keeps things afloat
Air resistance is a force that opposes motion through air. The quicker you travel, the bigger the air resistance:
The same applies to a body falling through a liquid (called “drag” or “upthrust”).
1) This animal is either ________ or moving with _____ _____…
2) This animal is getting _________…
3) This animal is getting _______….
4) This animal is…
Calculate the resultant force of the following:
500N
100N
700N
600N
50N
700N
700N
800N
800N
200N
100N
F
M
A
If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers:
Force (in N) = Mass (in kg) x Acceleration (in m/s2)
F
M
A
Consider a skydiver:
2) As his speed increases his air resistance will _______
3) Eventually the air resistance will be big enough to _______ the skydiver’s weight. At this point the forces are balanced so his speed becomes ________  this is called TERMINAL VELOCITY
Words – increase, small, constant, balance, accelerates
Consider a skydiver:
5) Because he is slowing down his air resistance will _______ again until it balances his _________. The skydiver has now reached a new, lower ________ _______.
Words – slowing down, decrease, increases, terminal velocity, weight
Parachute opens – diver slows down
Speed increases…
Terminal velocity reached…
On the Moon
New, lower terminal velocity reached
Diver hits the ground
Velocity
Time
Thinking distance
(reaction time)
Braking distance
Tiredness
Too much alcohol
Too many drugs
Poor visibility
Wet roads
Icy roads
Tyres/brakes worn out
Driving too fast
Momentum = Mass x Velocity
P
(in kgms1)(in kg)(in ms1)
M
V
Any object that has both mass and velocity has MOMENTUM. Momentum (symbol “p”) is simply given by the formula:
mv
Force = Change in momentum
(in kgm/s)
(in N)
Time
(in s)
F
T
Also called “impulse”
Newton’s second law of motion says that the force acting on an object is that object’s rate of change of momentum. In other words…
mv
F
T
Let’s use Newton’s Second Law to explain how airbags work:
W
M
g
Earth’s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N.
Weight = Mass x Gravitational Field Strength
(in N) (in kg) (in N/kg)
Thinking distance
(reaction time)
Braking distance
Tiredness
Too much alcohol
Too many drugs
Poor visibility
Wet roads
Icy roads
Tyres/brakes worn out
Driving too fast
W
F
D
When any object is moved around work will need to be done on it to get it to move (obviously).
We can work out the amount of work done in moving an object using the formula:
Work done=Forcexdistance moved
in J in N in m
Elastic potential energy is the energy stored in a system when work is done to change its shape, e.g:
Any object that moves will have kinetic energy.
The amount of kinetic energy an object has can be found using the formula:
Kinetic energy = ½ x mass x velocity squared
in J in kg in m/s
KE = ½ mv2
Momentum = Mass x Velocity
P
(in kgms1)(in kg)(in ms1)
M
V
Any object that has both mass and velocity has MOMENTUM. Momentum (symbol “p”) is simply given by the formula:
Speed = 50ms1
Speed = 20ms1
Speed = ??ms1
In any collision or explosion momentum is conserved (provided that there are no external forces have an effect). Example question:
Two cars are racing around the M25. Car A collides with the back of car B and the cars stick together. What speed do they move at after the collision?
Mass = 1000kg
Mass = 800kg
Mass = 1800kg
Momentum before = momentum after…
…so 1000 x 50 + 800 x 20 = 1800 x V…
…V = 36.7ms1
Speed = 20ms1
Mass = 1000kg
Mass = 800kg
Speed = 50ms1
What happens if the bodies are moving in opposite directions?
Momentum is a VECTOR quantity, so the momentum of the second car is negative…
Total momentum = 1000 x 50 – 800 x 20 = 34000 kgms1
Speed after collision = 34000 kgms1 / 1800 = 18.9ms1
α
241
237
Am
Np
4
95
93
2
Consider the nuclear decay of Americium241:
If the new neptunium atom moves away at a speed of 5x105 ms1 what was the speed of the alpha particle?
mv
Force = Change in momentum
(in kgm/s)
(in N)
Time
(in s)
F
T
Also called “impulse”
Newton’s second law of motion says that the force acting on an object is that object’s rate of change of momentum. In other words…
mv
F
T
Let’s use Newton’s Second Law to explain how airbags work:
+


+
Static electricity is when charge “builds up” on an object and then stays “static”. How the charge builds up depends on what materials are used:
+
+


+
+
+



+
+

+


Chimney
Negatively charged plates






Positively charged grid
+
+
+
Find out how static electricity is used in the following:
1) Photocopiers
2) Paint sprayer
Find out how static electricity is dangerous in the following situations:
1) Fuel pipes
2) Hospitals
Variable resistor
A
V
Diode
Switch
Bulb
Ammeter
Voltmeter
LDR
Resistor
Cell
Fuse
Thermistor
Battery
Note that electrons go from negative to positive
+

e
e
Electric current is a flow of negatively charged particles (i.e. electrons).
By definition, current is “the rate of flow of charge”
Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____.
Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta.
Resistance is anything that resists an electric current. It is measured in _____.
Words: volts, amps, ohms, voltage, ammeter, voltmeter
If a battery is added the current will ________ because there is a greater _____ on the electrons
If a bulb is added the current will _______ because there is greater ________ in the circuit
If the current here is 2 amps…
The current here will be…
The current here will be…
And the current here will be…
In other words, the current in a series circuit is THE SAME at any point
Here comes the current…
Half of the current will go down here (assuming the bulbs are the same)…
And the rest will go down here…
A PARALLEL circuit is one where the current has a “choice of routes”
And the current here will be…
The current here will be…
The current here will be…
The current here will be…
If the current here is 6 amps
V
If the voltage across the battery is 6V…
…and these bulbs are all identical…
V
V
…what will the voltage across each bulb be?
2V
V
If the voltage across the battery is 6V…
…what will the voltage across two bulbs be?
V
4V
If the voltage across the batteries is 4V…
What is the voltage here?
V
V
And here?
4V
4V
In a SERIES circuit:
Current is THE SAME at any point
Voltage SPLITS UP over each component
In a PARALLEL circuit:
Current SPLITS UP down each “strand”
Voltage is THE SAME across each”strand”
Resistance is anything that will RESIST a current. It is measured in Ohms, a unit named after me.
Georg Simon Ohm 17891854
V
Resistance = Voltage (in V)
(in ) Current (in A)
I
R
The resistance of a component can be calculated using Ohm’s Law:
Ammeter reads 2A
A
V
Voltmeter reads 10V
Resistance (Ohms, ) = Potential Difference (volts, V)
Current (amps, A)
Resistance is anything that opposes an electric current.
I
I
I
V
V
V
3. Diode
1. Resistor
A diode only lets current go in one direction – it has very high resistance in the other direction
Current increases in proportion to voltage
2. Bulb
As voltage increases the bulb gets hotter and resistance increases
Resistance
Resistance
Amount of light
Temperature
1) Light dependant resistor – resistance DECREASES when light intensity INCREASES
2) Thermistor – resistance DECREASES when temperature INCREASES
1.
4.
5.
2.
6.
3.
Earth wire
Live wire
Fuse
Neutral wire
Cable grip
Insulation
The neutral wire of a plug stays at a potential close to zero relative to the Earth
The live wire of a plug alternates between positive and negative potential relative to the Earth
V
DC stands for “Direct Current” – the current only flows in one direction:
Time
1/50th s
AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz)
230V
T
V
This number tells you how many seconds each square on the horizontal axis represents
This number tells you how many volts each square on the vertical axis represents
Q. What is the voltage and frequency of this supply?
Fuses are _______ devices. If there is a fault in an appliance which causes the ____ and neutral (or earth) wire to cross then a ______ current will flow through the _____ and cause it to _____. This will break the _______ and protect the appliance and user from further _____.
Words – large, harm, safety, melt, live, circuit, fuse
P
V
I
Power is “the rate of doing work”. The amount of power being used in an electrical circuit is given by:
Power = voltage x current
in W in V in A
Using this equation we can work out the fuse rating for any appliance. For example, a 3kW (3000W) fire plugged into a 240V supply would need a current of _______ A, so a _______ amp fuse would be used (fuse values are usually 3, 5 or 13A).
Copy and complete the following table:
E
P
T
The POWER RATING of an appliance is simply how much energy it uses every second.
In other words, 1 Watt = 1 Joule per second
E = Energy (in joules)
P = Power (in watts)
T = Time (in seconds)
Earth wires are always used if an appliance has a _____ case. If there is a _____ in the appliance, causing the live wire to ______ the case, the current “_______” down the earth wire and the ______ blows.
Words – fuse, fault, metal, surges, touch
Q
I
T
As we said, electricity is when electrons move around a circuit and carry energy with them. Each electron has a negative CHARGE. Charge is measured in Coulombs (C). We can work out how much charge flows in a circuit using the equation:
Charge = current x time
(in C) (in A) (in s)
E
V
Q
The amount of energy that flows in a circuit will depend on the amount of charge carried by the electrons and the voltage pushing the charge around:
Energy transferred = charge x voltage
(in J) (in C) (in V)
A hundred years ago people thought that the atom looked like a “plum pudding” – a sphere of positive charge with negatively charged electrons spread through it…
Ernest Rutherford, British scientist:
I did an experiment (with my colleagues Geiger and Marsden) that proved this idea was wrong. I called it the “Scattering Experiment”
Alpha particles (positive charge, part of helium atom)
Thin gold foil
Most particles passed through, 1/8000 were deflected by more than 900
Conclusion – atom is made up of a small, positively charged nucleus surrounded by electrons orbiting in a “cloud”.
ELECTRON – negative, mass nearly nothing
PROTON – positive, same mass as neutron (“1”)
NEUTRON – neutral, same mass as proton (“1”)
MASS NUMBER = number of protons + number of neutrons
4
He
SYMBOL
2
PROTON NUMBER = number of protons (obviously)
Notice that the mass number is different. How many neutrons does each isotope have?
16
O
17
18
O
O
8
8
8
Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more.
An isotope is an atom with a different number of neutrons:
A “radioisotope” is simply an isotope that is radioactive – e.g. carbon 14, which is used in carbon dating.
New nucleus
1) Alpha () – an atom decays into a new atom and emits an alpha particle (2 protons and 2 ______ – the nucleus of a ______ atom)
Unstable nucleus
New nucleus
Alpha particle
2) Beta () – an atom decays into a new atom by changing a neutron into a _______ and electron. The fast moving, high energy electron is called a _____ particle.
Beta particle
Unstable nucleus
3) Gamma – after or decay surplus ______ is sometimes emitted. This is called gamma radiation and has a very high ______ with short wavelength. The atom is not changed.
Words – frequency, proton, energy, neutrons, helium, beta
Unstable nucleus
New nucleus
Gamma radiation
More neutrons
Neutron
Unstable nucleus
Uranium or plutonium nucleus
New nuclei (e.g. barium and krypton)
Each fission reaction releases neutrons that are used in further reactions.
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