Additional Physics Key Points

• The steeper the line on a distance-time graph, the greater the speed it represents
• The slope on a distance-time graph represents speed
• If a car is travelling on a motor way, and every marker post it passes between takes 40s, it is travelling at a constant speed.

• Velocity is SPEED IN A GIVEN DIRECTION
• An object moving at a steady speed in a circle has a constant speed but its velocity is NOT constant because its direction of motion is constantly changing.
• A campervan travelling to scotland at a speed of 30 m/s has a different velocity to a campervan travelling to cornwall for a beach party at 30 m/s. they have the same speed but different velocities because they are travelling in different directions.

• The acceleration of an object is its change in velocity per second

• The gradient of a line on a velocity-time graph represents the acceleration of the object
• The area under a velocity-time graph represents the distance covered

• For and Object moving at a constant speed, the graph is a straight line.
• The speed is represented by the slope of the line
• To find the slope, we draw a triangle under the line
• The height of the line represents the distance travelled
• The base represents the time taken
• To find the objects speed you do:
  • the height of the triangle divided by the base of the triangle
• THIS ONLY WORKS FOR A CONSTANT SPEED

• For a moving object with a changing speed, you can see if the speed increased gradually or no depending on slope of the line.

TBH, rather do Potions with Snape than Physics with Ed.

• The slope on a velocity-time graph represents the acceleration
• This is because ACCELERATION = CHANGE OF VELOCITY DIVIDED BY TIME TAKEN
• To Find the distance travelled, work out the area beneath the line

• Whenever two objects push or pull on eachother, they exert equal ond opposite forces on one another.
• The unit of a force is in NEWTONS

• An object may have several different forces acting on it, which can have different strengths and directions. But they can be added together to give the resultant force. This is a single force that has the same effect on the object as all the individual forces acting together.

• When all the forces are balanced, the resultant force is zero. In this case:

  • a stationary object remains stationary
  • a moving object keeps on moving at the same speed in the same direction

• When all the forces are not balanced, the resultant force is not zero. In this case:

  • A stationary object begins to move in the direction of the resultant force.
  • A moving object speeds up, slows down or changes direction depending on the direction of the resultant force.
• If a body is accelerating, it can be speeding up, slowing down or changing direction.
• If a body is accelerating, there must be a resultant force acting on it
  

Example: A chicken starts from rest and accelerates along a straight flat road.

• The force of air resistance on it is less than the motive force of its engine
• The resultant force is greater than zero
• The downward force of the chicken on the road is equal to the support force of the road on the chicken

• resultant force (newton, N) = mass (kg) × acceleration (m/s²)
• If the velocity of an object changes, it must be acted upon by a resultant force
• If the velocity increases, the resultant force is in the same direction as the velocity
• If the velocity decreases, the resultant force is in the opposite direction as the velocity

• For any car travelling at a constant velocity, the resultant force is zero
  • This is because the motive force of the engine is balanced with the resistive forces on it like air resistance and friction etc.

• The braking force needed to stop a vehicle depends upon:
  • The velocity of the vehicle when the brakes are applied
  • The mass of the vehicle
• The greater the velocity, the greater the deceleration needed to stop it in a certain distance. So the braking force must be greater at a low velocity.
• The greater the mass, the greater the braking force needed for a given decelaration.

• Stopping distances are the shortest distance a vehicle can safely stop in. it is split into two parts:
  • The thinking distance
  • The braking distance

The Stopping Distance = the Thinking Distance + the Braking Distance

It takes a certain amount of time for a driver to react to a hazard and start applying the brakes. During this time, the car is still moving. The faster the car is travelling, the greater this thinking distance will be.

The thinking distance will also increase if the driver's reactions are slower because they are:

• under the influence of alcohol
• under the influence of drugs
• tired

The braking distance is the distance the car travels from where the brakes are first applied to where the car stops. If the braking force is too great, the tyres may not grip the road sufficiently and the car may skid. The faster the car is travelling, the greater the braking distance will be.

The braking distance will also increase if:

• The brakes or tyres are worn.
• The weather conditions are poor, such as an icy or wet road.
• The car is more heavily laden, for example, with passengers and luggage.

• Weight is due to the gravitational force of attraction between objects and the earth
• This force is weaker at the poles and the equator, so you will weigh less if you are here, but your mass is the same wherever you are, even if you are a fat man on the Moon.

• This guys mass will be the same, but he would weight less if he stood at the equator. he would weigh even less if he was on the moon (if they could get him up there) lol. in the exam just think of him floating around in space with his burger...                                                                      

• The weight of an object is the force of gravity on it
• The mass of an object is the quantity of matter in it

weight (N) = mass (kg) × gravitational field strength (N/kg)

weight (N) = mass (kg) × gravitational field strength (N/kg)

weight (N) = mass (kg) × gravitational field strength (N/kg)

weight (N) = mass (kg) × gravitational field strength (N/kg)

weight (N) = mass (kg) × gravitational field strength (N/kg)

(Remember this, dude.)

• If you drop a banana abouve the ground, it falls because of its weight
• If the banana falls freely, no other forces act on it, so the resultant force on it is its weight
• It accelerates downward at a constant acceleration of 10 m/s2
• For example, if we release a 1kg banana abouve the ground:
  • the force of gravity on it is 10N
  • its acceleration (=force/mass=10N/1Kg) = 10m/s2

• If a banana falls in a fluid, the fluid drags on the object
  • the drag force increases with speed
  • the resultant force on the object = weight - drag force
  • in air, the drag force is air resistance
• The acceleration of the banana decreases as it falls
  • this is because the drag force increases as it speeds up, so the resultant force decreases
  • the banana reaches constant velocity when the drag force is  = its weight. This is terminal velocity. The acceleration and the resultant force is zero

• When an object is moved by force, we say work is done by the object. The force transferres energy to the object

Work Done = Energy Transferred

• The work done depends on the force and the distance moved

Work Done(J) = Force(N) X Distance Moved in the Direction of the Force(M)

• Work done to overcome friction is mainly transformed into heat energy

• The kinetic energy of an object is its energy due to motion

Kinetic Energy(J) = 1/2 x Mass(Kg) x Speed2 (m/s2)

• When you stretch a bowstring, the work you do is stored in it as elastic potential energy. This can be transformed into Kinetic Energy
• An object is elastic if it regains its shape
• Elastic Potential energy is the energy stored in an elastic object when work is done on it to change its shape

The Momentum of a moving object = its mass x its velocity

• Momentum is conserved whenever objects interact, provided that no external forces act on them
• If a vehicle crashes into the back of a line of cars, each car in turn is shunted into the one in front. Momentum is transferred along the line of cars to the one at the front.

• Momentum has size and direction
• When two objects push each other apart, they move apart in equal and opposite directions
• If you throw a stone, you are giving it momentum
  

You need to be able to calculate the force involved in changing the momentum of an object. Here is the equation you need:

The force is measured in newtons, N. The time is measured in seconds, s.

You should see that, for a given change in momentum, the longer the time taken, the smaller the force needed. This is the idea behind many car safety features. It also explains why it takes a long time to stop a super-tanker at sea, or to change its direction.

• Like charges repel, Unilike charges attract
• Insulating materials that lose electrons when rubbed. become positively charged
• Insulating materials that gain electrons when rubbed, become negatively charged

• The rate of flow of electrical charge is called the current
• Metals conduct electricity because they contain delocalised electrons which move about freely in the metal
• Insulators cant conduct electricity because all the electrons are held in atoms

• A conductor can only hold charge if it is insulated from the ground
• To charge an insulated conductor, it needs to be brought into contact with an insulated object.
  • If the object is posotively charged, electrons transfer from the conductor to the object, making the conductor positive because it LOSES electrons
  • If the object is negitively charged, electrons transfer to the conductor from the object. so the Conductor becomes NEGITIVELY charged because it GAINS electrons

• If we supply a conductor with more and more charge, its electrical potential energy increases. The potential difference between the conductor and the ground increases
• If the potential difference becomes high enough, a spark may jump between the object and a nearby earthed object. (a metal object is earthed by connecting it to the ground)

The Electrostatic paint sprayer.

• Automatic paint sprayers are used to paint metal panels
• They Charge the panels
• Then they oppositely charge the paint.
• The paint droplets repel eachother - making them spread out giving a more even coat
• The paint droplets are attracted to the plate

Pipes.

Whena road tanker pumps oil or petrol into a storage tank, the pipe must be earthed. If it isnt, the pipe could become charged and a build up of charge could cause a spark. this could make an explosion.

Static electricity is also generated when grains of powder are pumped through pipes. Friction between the grains and the pipe charges them. An explosion could happen due to a spark igniting the powder.

Antistatic Floors.

Doctors use anaesthetic explosions during operations. some of these gases are explosive. If the gas escapes, it may explode. To eliminate Static charge in operating theatres, an antistatic material is used on the floor. It is a poor insulator so it conducts charge to the Earth.

• Electrical circuits can be represented by circuit diagrams. The various electrical components are shown by using standard symbols in circuit diagrams. Components can be connected in series, or in parallel. The characteristics of the current and potential difference (voltage) are different in series and parallel circuits.
• Each component has its own symbol
• A ciruit diagram shows  how components are connected together
• A battery consists of two or more cells connected together

• Firstly, pretend that the rectangle is a bulb. (only decent pic on google :p)
• The ammeter measures the current through the bulb. It is connected in a series with the bulb so that the current trough them is the same
• The Voltmeter measures the potential difference accross the bulb. it is connected in parrellel with the bulb.
• Electrons passing through the bulb have to push their way through lots of vibrating atoms. The atoms resist passage of electrons through the bulb.
• We define the RESISTANCE of an elecrical component as:
  • Resistance(O) = Potential difference(V) / Current (A)
  • The unit of resistance is the Ohm
• The current through a resistor at constant temperature is directly proportional to the potential difference accross the resistor
  

• Filament lamp: resistance INCREASES with INCREASE of the filament temperature
• Diode:
  • FORWARD resistance LOW
  • REVERSE resistance HIGH
• Thermistor: resistance DECREASES if its temperature INCREASES
• LDR: resistance DECREASES if the light intensity on it INCREASES

• The total potential difference of the voltage supply in a series circuit is shared between the components
• The same current passes through each component in a series circuit
• The total potential difference of cells in a series is the sum of the potential difference of each cell
• The total resistance of components in a series is equal to the sum of their seperate resistances.

• REMEMBER: in a series circuit, the same current passes through all of the components

• Components that are connected one after another on the same loop of the circuit are connected in series. The current that flows across each component connected in series is the same.
• The circuit diagram shows a circuit with two lamps connected in series. If one lamp breaks, the other lamp will not light.

• The total current through the whole circuit is the sum of the currents through the seperate components
• For components in Parrallel, the potential difference across each component is the same
• The bigger the resistance of a component, the smaller the current is

Current = Potential Difference / Resistance

• Components that are connected on separate loops are connected in parallel. The current is shared between each component connected in parallel.
• The circuit diagram shows a circuit with two lamps connected in parallel. If one lamp breaks, the other lamp will still light.

Which is parrallel and which is series? 

• When you switch on a light at home, it has an alternating current, becuase mains electricity is an alternating current supply.
• An alternating current repeatedly reverses its direction - it flows one way and then the other way
• A mains circuit has a live wire which is alternately a positive and negative cycle and a neutral wire at zero volts.
• The live wire is dangerous because it is potential
• Mains electricity is an alternating current supply

• Have cases made out of stiff plastic
• The pins are made of brass because:
  • Brass is a good conductor
  • Brass des not oxidise or rust
  • Copper is not used because it isnt as hard as brass
• The case material is an electrical insulator
• The plug contains a fuse between the live pin and the live wire. The fuse melts and cuts off the live wire if too much current passes through

• A fuse contains a thin wire that heats up and melts cutting off the current, if too much current passes through it.
• A circuit breaker is an elecromagnetic switch that trips/opens and cuts the current off, should too much current pass through

• The power supplied to a device is the energy transfer to it each second
• Elecrical Power supplied = Current x Potential Difference

• An electric current is the rate of flow of charge
• When charge flows through a resistor, electrical energy is transferred as heat
• Charge = Current x Time
• Energy Transferred = Potential Difference x Charge Flow

NUCLEAR PH**ICS

Man, gotta love Ice age...

• OK, you already know about Protons, Nuetrons and Electrons from chemistry
• An uncharged atom has equal numbers of protons and electrons
• An atom with unequal protons and electrrons is an ion
• Isotopes are atoms of the same element  with different numbers of the nuetrons

cwotei mie fisicx Teecher hoo tawwt mei hoooh tu speeaarwl

" chemists are interested in the pretty little elecrons dancing around, whilst the physicists are interested in the real stuff. that is the nucleus"

• An unstable nucleus becomes more unstable by emmiting:

• Alpha particles in a beam are sometimes scattered through large angles when they are directed at a thin metal foil
• Scientists used to think that a nucleus was like a plum pudding with:
  • the posotively charged matter spread evenly
  • electrons buried inside
•  This random guy called Rutherford used measurments from the alpha particles to prove that an atom has a small positively charged central nuleus where most of the mass of an atom is located.

Nuclear power reactors use a reaction called nuclear fission. Two isotopes in common use as nuclear fuels are uranium-235 and plutonium-239.

Fission is another word for splitting. The process of splitting a nucleus is called nuclear fission. Uranium or plutonium isotopes are normally used as the fuel in nuclear reactors, because their atoms have relatively large nuclei that are easy to split, especially when hit by neutrons.

When a uranium-235 or plutonium-239 nucleus is hit by a neutron, the following happens:

1. the nucleus splits into two smaller nuclei, which are radioactive
2. two or three more neutrons are released
3. some energy is released

The additional neutrons released may also hit other uranium or plutonium nuclei and cause them to split. Even more neutrons are then released, which in turn can split more nuclei. This is called a chain reaction. The chain reaction in nuclear reactors is controlled to stop it going too fast.

Nuclear fusion involves two atomic nuclei joining to make a large nucleus. Energy is released when this 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. Here is one nuclear fusion reaction that takes place:

hydrogen-1 nuclei fuse with hydrogen-2 nuclei to make helium-3 nuclei

• Nuclear fusion occurs when two nuclei are forced so close they form a single larger nucleus.
• Energy is released when two light nuclei are forced together
• A fusion reactor needs to be at a high temperature before nuclear fusion can take place