1. PHYSICS UNIT 2

2. Distance-Time Graphs
The line is straight - this means that the object is moving at a constant speed (40 seconds to go every 1000m)
If the car had gone faster then the line would have been steeper. In other words the gradient would have been greater (would have gone further than a 1000m every 40 seconds)
The gradient of a line on a Distance-Time graph represents speed

3. Y and Z went at a constant speed because the lines are straight
X went the fastest because its gradient is greatest
Part of Z’s line is straight – this means the object is stationary (the car stopped)

4. Calculating Speed SPEED = Distance / Time Distance in metres
Time in seconds
Speed is m/s (metres per second)
Distance – 1000m
Time – 40 seconds
Speed = 1000/40 = 25m/s

5. Calculating Speed Speed of Y = 30,000 / 1250 = 24m/s
For Z you can only work out the average speed
Speed of Z = 20,000 / 1500 = m/s

6. Velocity is speed in a given direction
What is Velocity?
An object moving at a constant speed in a straight line has a constant velocity
An object moving in a circle at a constant speed does not have a constant velocity
Velocity is speed in a given direction
Cars travelling at the same speed in different directions have different velocities

7. What is Acceleration? Acceleration is change of velocity per second
Unit is metres per second squared

8. The greater the gradient – the greater the acceleration
Velocity-Time Graphs
The greater the gradient – the greater the acceleration

9. Calculating change in velocity
Change of velocity = Final velocity (v) – initial velocity (u) Change of velocity = v - u

10. Calculating Velocity
Acceleration (A) = Change in velocity Time taken for the change (T) Acceleration (a) = v-u t

11. The area under the line on a velocity-time graph represents distance travelled

12. What is a force? The unit is Newton (N)
A force can change the shape of an object. It can change its state of rest. It can change its motion
The unit is Newton (N)

13. Resultant Force
We can work out the effect of the forces acting on an object by replacing them with a single force, the resultant force This is a single force that has the same effect as all the forces acting on an object

14. Zero Resultant Force
If an object remains stationary then the resultant force is zero
If the object continues to move at the same velocity then the resultant force is zero
In this case: If only two forces act on an object, they must be equal to each other and act in opposite directions

15. Calculating Resultant Force
Resultant force is their difference if the forces act in opposite directions
Resultant force is the sum of the two forces if they act in the same direction

16. Calculating Resultant Force
Resultant Force (F) = Mass (M) x Acceleration (A) Resultant Force in Newtons Mass in Kilograms Acceleration in metres/second squared
The greater the mass of an object, the smaller its acceleration is for a given force

17. Breaking Force
Breaking force to stop a vehicle = Mass * Acceleration Acceleration when the breaks are first applied

18. Stopping Distances
Shortest distance a vehicle can safely stop Stopping distance = Thinking Distance + Braking distance

19. What increases thinking distance?
Poor reaction time (Tired / Alcohol / Drugs)
High speed

20. What increases braking distance?
High speed
Poor weather conditions
Poor maintenance

21. We can solve this using speed cameras
Fall in speed by 17%
55% reduction in deaths and serious injury

22. How to prevent skidding when breaking
Anti skid surfaces
Rougher
This increases friction
Reduces skidding when breaking hard
Used at junctions

23. What is Weight? Weight of an object is the force of gravity on it
Mass of an object is the quantity of matter in it

24. Calculating Weight Weight = Mass * Gravitational Field Strength
Weight in Newtons (N)
Mass in Kg
Gravitational Field Strength in N/Kg

25. Where will you weigh less?
The gravitational field strength is weaker at the equator
If you want to reduce your weight, go to the equator

26. Releasing an object
When you release an object it falls because of its weight
Weight is the resultant force

27. Releasing an object into liquid
Drag force acts in the opposite direction to the weight of the object
Resultant Force = Weight – Drag Force
As it falls the acceleration will decrease
It will reach a constant velocity when the Drag Force = Weight. The resultant force will be zero
This velocity is its TERMINAL VELOCITY

28. What is an Elastic Object?
It is an object that regains its original shape
For example rubber

29. Extension
Increase in length of an elastic object is known as extension
Extension = New length – Original length

30. Hooke’s Law
Extension of a spring is directly proportional to the force applied
As long as the limit of proportionality is not exceeded
It obeys Hooke’s law

31. Energy and Work
Work is done on an object when a force makes the object move
Energy transferred = work done
Work done (joules) = force (newtons) x distance moved in the direction of the force (metres)

32. Gravitational Potential Energy
This increases when the object goes up and decreases when it goes down
Change of gravitational potential energy = mass * gravitational field strength* change in height

33. Kinetic Energy and Momentum
Kinetic energy (J) = ½ * Mass (Kg)* Speed (m/s)²
Momentum (Kg m/s) = Mass * Velocity
In a closed system, the total momentum before an event is equal to the total momentum after an event

34. Inside an atom In the nucleus there are protons and neutrons
Electrons move around the nucleus

35. PROTONS – Positive charge
ELECTRONS – Negative charge
NEUTRONS – Uncharged
Equal number of electrons and protons means that the object is UNCHARGED
Objects become charged if electrons or added or lost
STATIC ELECTRICITY

36. Adding electrons makes it negative – more electrons than protons
Removing electrons makes it positive – more protons than electrons

37. Electric Current
This is a flow of electrons around a circuit (flow of charge)
Move from negative end of battery (repelled from it) to positive end of battery
They transfer energy from the battery to the bulb
Battery is two or more cells connected together
In a circuit every component has an agreed symbol
A circuit diagram shows how they are linked together

39. Calculating Electric Current
Electric current is the flow of charge (flow of electrons) per second
More electrons = More current
Current = Charge flow / Time
I = Q/T
I is current in amperes (A)
Q is charge in coulombs (c)
T is time in seconds (s)

40. Ammeter Ammeter measures current
In this case it measures the current going through the bulb (flow of electrons which carry the energy)

41. Voltmeter
Voltmeter measures the potential difference across the torch bulb
This is the amount of energy transferred to the bulb by each coulomb of charge
It is called voltage
The unit is volts (V)

42. Calculating Voltage Voltage = Work done /charge V = W/Q
V is Voltage in volts (V)
W is work done in Joules (J)
Q is charge in Coulombs (C)

43. What is Resistance?
Electrical components RESIST the passage of electrons
Resistance = Voltage /Current
R = V/I
R is Resistance in Ohms
V is Voltage in Volts
I is current in amperes

44. OHMS Law
The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor
Double the voltage – double the current
This means that the resistance is constant
Changing the current does not change the resistance

45. Series: Parallel: Current Potential Difference Cells Resistance
Same current passes through components in series with each other
Current splits. Thus total current is sum of the currents
Potential Difference
This is shared between the components. Thus you add the potential differences to get the total potential difference
This is the same for each component in parallel
Cells
Add the potential difference from each of the cells together to get the total potential difference
Resistance
Add resistances to get total resistance
The bigger the resistance the smaller the current

46. The battery in a torch makes the current go round the circuit in one direction only. This is called DIRECT CURRENT (dc)
At home you use ALTERNATING CURRENT (ac) which means the current repeatedly reverses direction. It flows one way and then the opposite way.
Its FREQUENCY is the number of cycles it passes through each second
An OSCILLOSCOPE measures this
Frequency = 1 / Time taken for one cycle
Frequency = 1/0.02 = 50Hz

47. Cables Every mains circuit has a LIVE wire and a NEUTRAL wire
The live wire alternates between + and – volts
The neutral wire is always at 0V

48. Earth Wire Live wire touches the metal case
Big current will flow from the live into the metal case
This will give you an electric shock
The metal case is attached to the Earth wire
The earth wire takes the current away and blows the fuse.
The fuse in the plug must be in series with the appliance. The fuse melts.
Alternatively there is a circuit breaker which pulls a switch open

49. Plugs Remember the colours
Cable grip and case and made of plastic because they are good insulators
Wall sockets are connected in parallel

50. POWER = Energy transferred / Time – UNIT IS WATTS (W)
2. POWER SUPPLIED = Current * Potential Difference – UNIT IS VOLTS (V)
3. CORRECT RATING FOR A FUSE = Electrical power / Potential Difference
4. CHARGE = Current * Time – UNIT IS COULOMBS (C)
5. ENERGY TRANSFERRED = Potential difference * Charge – UNIT IS JOULES

51. Atoms have a nucleus that are unstable.
They become stable by emitting particles

53. 2 protons and 2 neutrons stuck together Positively charged
Alpha
2 protons and 2 neutrons stuck together
Positively charged
Beta
Fast moving electron
Negatively charged
Gamma
Electromagnetic radiation
Uncharged

54. Nuclear Reactions Atomic number: Number of protons in a nucleus
Mass number: Number of protons and neutrons
Number of neutrons = Mass number – Atomic number
Alpha emission reduces the atomic number by 2 and the mass number by 4
Beta emission adds 1 to the atomic number and does not change the mass number

55. Half life is the time it takes for the number of nuclei of an isotope (mass of atoms to half)

56. What are the uses of radioactivity?
Measure thickness
Trace the flow of a substance through a system
Find the age of an ancient material

57. Nuclear Fission
Nucleus releases 2 or 3 neutrons and energy (radiation)
This causes other nuclei to split – CHAIN REACTION
This happens in a nuclear reactor
The energy is used to generate electricity
Uses Urannium-235 or Plutonium-239

58. Nuclear Fusion
Small nuclei are fused into large nuclei (for example hydrogen)
This releases energy
It happens in stars and the sun
Could do this with water – lots of hydrogen atoms
The nuclei need to move fast or they will repel

59. The birth of the universe
13 billion years ago- THE BIG BANG
A hot glowing ball of radiation and matter were created
The university expanded and the temperature fell – it became cold and dark – THE DARK AGES
Uncharged matter was attracted to one another and formed gigantic clumps
This became galaxies and stars

60. The Birth of the Universe
13 billion years ago- THE BIG BANG
A hot glowing ball of radiation and matter were created
The university expanded and the temperature fell – it became cold and dark – THE DARK AGES
Uncharged matter was attracted to one another and formed gigantic clumps
This became galaxies and stars

61. The Life Cycle of a Star
Gravity pulls dust and gas together. This forms a PROTOSTAR
As it gets denser –it gets hotter
Nuclear fusion changes hydrogen to helium. This is the MAIN SEQUENCE. The star is stable because the force of gravity is balanced by the outward force of radiation.
Star runs out of hydrogen
Those the same size of the sun swell out, cool down and turn red. This is called a RED GIANT
Gravity then causes it to collapse in on itself. It heats up and turns white. This is called a WHITE DWARF
It then goes cold and becomes a BLACK DWARF
Those bigger than the sun swell out and become a RED SUPERGIANT
It starts to collapse but then explodes in a massive explosion called a SUPERNOVA
Most then become NEUTRON STARS. Very heavy stars create a BLACK HOLE