# Physics 2

Helpful Notes created by notes submitted on get revising - all formulas at the back which might be helpful :)

## Representing Motion

Distance Time Graphs

- The Slope of a Distance Time Graph Represents Speed
- Speed(m/s) = Distance(m)/Time(s)
- When an object is stationary the line on the graph is horizontal(flat)
- When an object is moving at a steady speed the line is straight but sloped.
- Distance is on the Y axis and Time is on the X axis

## Representing Motion

Velocity Time Graphs

- The velocity of an object is its speed in a given direction
- The slope on a velocity time graph represents Acceleration
**VELOCITY IS SPEED IN A GIVEN DIRECTION****ACCELERATION is change of velocity per second**- Acceleration(m/s/s) = Change in Velocity / Time
- When an Object is moving with constant velocity the line on the graph is horizontal
- When an Object is moving with constant acceleration the line is straight but slopped
- The Gradient of a velocity-time graph represents Acceleration
**The Area under a velocity time graph represents Distance Travelled**

## Newtons three laws of motion

**Newtons Three Laws of Motion**

- 1. Every Object in steady motion tends to remain in that state unless an external force applies to it
- 2.The relationship between an objects mass (m), its acceleration (a), and the applied force (F) can be represented by the equation
**Resultant Force(N)=mass(kg)xacceleration(m/s2)**- IF THERE IS AN UNBALANCED FORCE , THEN THE OBJECT WILL ACCELERATE IN THAT DIRECTION
- 3. for every action there is an equal and opposite reaction
- if you push against a wall, the wall will push back at you at the same force you applied to it
- the faster a body moves through a fluid, the greater the frictional force acting on it.
- a body falling through a fluid will intitailly accelerate due to the force of gravity.
- EVENTUALLY THE RESULTANT FORCE ON A BODY WILL BE ZERO THEREFORE WILL FALL AT ITS TERMINAL VELOCITY

## Work done

**Work-done**

- When a force causes a body to move through a distance, energy is transformed and work is done.
**WORK DONE(JOULES) = FORCE APPLIED(NEWTONS) X DISTANCE TRAVELLED(METRES)**- WORK DONE AGAINST FRICTION IS MAINLY TRANSFORMED TO HEAT
- for an object to recover its original shape, elastic potential is the energy stored in an object when work is done on the object to change its shape
- the kinetic energy of a body depends on its mass and speed
**KINETIC ENERGY(Joules) = 1/2 MASS(kg) X VELOCITY squared(m/s/s)**

## Momentum and Collisons

- The faster a body is moving the more kinetic energy is has
- It also has MOMENTUM
- When working out what happens to a bodie as a result of a collison/explosion it is more useful to think of it in momentum rarther than energy
- Momentum,Mass and Velocity Can be related by the equation
**Momentum(kgm/s) = Mass x Velocity**- Momentum has both MAGNITUDE AND DIRECTION
- Momentum is conserved in any Collision/Explosion provided no external forces act upon it
- When a force acts on an object it causes a change in momentum
- the larger the force, the faster the change of momentum
**FORCE ACTING = CHANGE IN MOMENTUM / TIME TAKEN FOR CHANGE**- Crumple zones crumple on impact. this increses the time taken for the car to stop
- Seatbelts stretch slighlty . this increses the time taken to stop . it reduces the forces acting upon there chest
- Airbags alow you to slow down more gradually

## Static Electricty

Static Electricity

- Some insulating Materials become electrically charged when they are rubbed together
- Charges that are the same repel, whilst unlike (opposite) charges attract.
- When certain insulating materials are rubbed against each other they become electrically charged.
- Negatively charged electrons are rubbed of one material onto the other
- The material that gains electrons becomes negatively charged
- The material that loses electrons becomes positivly charged
- When two electricly charged objects are brought together, they exert a force on each other
- Electrical Charges can move easily through some substances , e.g metals
- The rate of flow of electrical charge is called current.
- A Charged body can be discharged by connecting it to earth with a conductor
- Charge then flows through the conductor
- The greater the charge on an isolated body the greater the potentinal differance beetween the body and the earth
- If the potential differance becomes high enough a spark may jump across the gap beetween the body and any earthered conductor that is brought near it.

## Electrical Circuits

- Two things are important for a circuit to work: there must be a complete circuit, there must be no short circuits
- The current that flows through a circuit in series is the same
- The P.D(Voltage) that flows through a circuit in series is shared
- The current that flows through a circuit connected in parallel is shared
- The P.D that flows through a circuit in parallel is the same
- Current-Potential Difference Graphs are used to show-how the current through a component varies with the P.D across it
- The Current through a Resistor (at a constant temperature) is directly proportional to the P.D across the resistor
**P.D = CURRENT X RESISTANCE**- The resistance of a filament lamp increases as the temperature increases
- the resistance of a thermister decreses as the temperature increses
- the resistance of a LDR (Light Dependant Resistor) decreases as light intensity increases
- The current through a componant depends on its resistance
- The greater the resistance the smaller the current for a given P.D accross the componant

## Electrical Circuits...

Current-Potential difference graphs are used to show how the current through a component varies with the potential difference across it

- The current through a resistor(at a constant temperature) is directly proportional to the potential difference across the resistor
**P.D(Volts) = CURRENT(Amps) X RESISTANCE(Ohms)**- The resistance of a filament lamp increases as the temperature of the filament lamp increases
- The current through a diode flows in one direction only, the diode has a high resistance in the reverse direction
- The resistance of an LDR decreases as light intensity increases
- The resistance of a Thermister decreases as temperature increases
- The current through a componant depends on its resistance.
- The greater the resistance the smaller the current for a given P.D across the compant

## Mains Electricity

Cells and batteries supply current which flows in one direction, this is called direct current or d.c

**An alternating current is one that is constantly changing direction****A Direct current is one that flows in one direction only**- Mains electricity is a.c supply
- In the UK, it has a frequency of 50 cycles per second (50 hertz)
- UK mains supply is 230Volts
- If an electrical fault causes too great a current the circuit should be switched off by a fuse
- When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit
- Appliances with metal cases are usally earthed
- The earth wire and the fuse together protect the applience and the user
- The live terminal of the mains supply alternates beetween positive and negative potential with respect to the neutal terminal
- the neutral terminal stays at a potential close to zerowith respect to the earth
**Frequency(Hz) = 1/Time Period(peak to peak)**

## Electrical Appliances

- Electrical Appliances Transform energy
- The power of an electrical appliance is the rate at which is transforms energy
- Most appliances have their power and the potential difference of the supply printed on them
- FROM THIS WE CAN CALCULATE THEIR CURRENT AND THE FUSE THEY NEED
- Electric current is the rate of flow of charge
- When an electrical charge flows through a resistor, electrical energy is transformed into heat energy
- The rate at which energy is transformed in a device is called the power
**Power(Watts) = Energy Transformed(Joules) / Time(Secounds)**- Power, P.D and current are related by the equation
**POWER = CURRENT X P.D**- energy transformed , p.d and charge are related by the equation
**ENERGY TRANSFORMED(JOULES) = P.D(VOLTS) X CHARGE(COULOMBS)**- the amount of electrical charge that flows is related to current by the equation
- CHARGE = CURRENT X TIME

## Atomic Structure (Works of other Scientists)

- In 1804, John Dalton agreed with Democritus that matter was made up of tiny spheres that could not be broken up
- Nearly 100 years later, JJ Thompson discovered that electrons can be removed from atoms
- He suggested that atoms were spheres of positive charge with negatively charged neutrons stuck in them like plums in a plum pudding
- However in 1909 Rutherford tried firing alpha particles at thin gold foil, most of them went through but some were deflected
- He then came up with the Nuclear model of the atom
- The nuclei of some atoms are unstable
- The can split or decay and release radiation
- Such isotopes are called Radioactive Isotopes/Radioisotopes
- When radioactive isotope decays it forms a different atom with a different number of protons
- When an atom emits alpha/beta radiation its nucleus changes
- it becomes the nucleus of a different element
- this is because the number of protons determines what type of atom it is

## Alpha and Beta Decay

**Alpha decay**

Change in nucleus - Nucleus loses 2 protons and 2 neutrons

Particle Emitted - 2 protons and 2 neutrons emitted as an alpha particle

**Beta Decay**

Change in nucleus - a neutron in the nucleus changes into a proton

Particle Emitted - an electron is created in the nucleus and instantlly emitted

IN EACH CASE A DIFFERENT ELEMENT IS LEFT BEHIND

## Nuclear Fisson and Fusion

Nuclear Fission - ** the splitting of atomic nuclei** and is used in nuclear reactors as a source of heat energy which can be transformed to eletrical energy

Nuclear Fusion - * the joining together of atomic nuclei* and is the process by which energy is released in stars

URANIUM- 235 AND PLUTONIUM-239 istopes are normally used as the fuel in nuclear reactors , because their atoms have relativly large nuclei that are easy to split, expecially when hit with neutrons.

**ENERGY IS RELEASED IN NUCLEAR REACTOR AS A RESULT OF A PROCESS CALLED NUCLEAR FISSION**

**THIS EVENT CAN CAUSE OTHER FISSONABLE NUCLEI TO SPLIT, SO PRODUCING A CHAIN REACTION OF EVENTS**

The nuclei undergoing fission splits into two smaller nuclei and 2 or 3 neutrons and energy is released

## Nuclear Fussion

**THE JOINING TOGETHER OF TWO ATOMIC NUCLEI TO FORM A LARGER ONE**

- IT IS THE PROCESS BY WHICH ENERGY IS RELEASED IN STARS

- IT INVOLVES TWO ATOMIC NUCLEI JOINING TOGETHER TO MAKE A LARGE NUCLEUS

- ENERGY IS RELEASED WHEN TIS HAPPENS

- THE SUN AND OTHER STARS USE NUCLEAR FUSION TO RELEASE ENERGY

- THE SEQUENCE OF NUCLEAR FUSION REACTIONS IN A STAR IS COMPLEX, BUT OVERALL **HYDROGEN NUCLEI JOIN TO FORM HELIUM NUCLEI**

## ALL FORMULA

FORCES AND MOTION

- Speed(m/s) = Distance(metres)/ Time(seconds)
- Acceleration(m/s2) = Change in Velocity(m/s)/Time Taken(seconds)
- Weight(Newtons) = Mass(kg) x Gravitational Field Strength(N/kg)
- Resultant Force(Newtons) = Mass(kg) x Acceleration(m/s2)
- Thinking distance + Braking distance = Stopping Distance
- Work done(Joules) = Force Applied(Newtons) x Distance Moved(Metres)
- Kinetic Energy(Joules as it is energy) = 1/2 Mass(kg) x Velocity Squared (m/s)
- Momentum(kgm/s) = Mass(kg) x Velocity(m/s)
- Force Acting(n) = Change in momentum(kgm/s)/time taken for change to happen

ELECTRICITY

- RESISTANCE = P.D / CIRRENT
- Frequency (Hz) = 1/Time Period(s)
- Energy = Power x Time
- Power = Voltage x Current
- Total charge(coulombs) = current x time
- Energy tranformed = Charge x P.D

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