Physics Paper 1

Newton's 1st and 2nd Laws

  • 1st Law - a resultant force is needed to make something speed up, slow down or start moving.
  • 2nd Law - Force = mass x acceleration
  • Larger deceleration can be dangerous. The force can be lowered by slowing the object now over a long time.Vehicles have crumple zones, seat belts and air bags to prevent the dangers of large deceleration. The brakes help by transferring from the vehicle's kinetic energy stores to the thermal energy store of the brakes. Very large decelerations can cause the brakes to heat and make the car skid.

Mass (kg) - the amount of stuff in object. Weight (newtons) - is amount of force acting on the object due to gravity. Close to the earth, this force is caused by the gravitational field of the Earth. Centre of mass - the point where you assume the whole mass is concentrated. Weight can be measured using a calibrated spring balance.

Weight = mass x gravitational field strength. On Earth: 10n/kg

Circular motion - when an object is travelling in a circle, it's constantly changing direction and so also changing velocity (accelerating) - must be resultant force acting on it and it's at centre of circle. This is known as centripetal force.

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Motion

  • You can measure people's speed using lightgates, measuring tape and frames per second. Average speed of walking: 3mph, average speed of running: 8mph, average speed of car: 40mph.
  • Inertia - stationary objects until acted on by resultant forces will stay at rest. Inertia is when something is unchanged - inertia mass measures how difficult it is to change the velocity of an object and can be found using mass = force divided by acceleration. 

Newton's Third Law - when two objects interact, the forces they exert on each other are equal and opposite. However, the force can exerted on something with a smaller weight and cause it to accelerate. For example, skater A (55kg) pushes on skater B (70kg ) using her hand and feels an equal push (normal contact force). However, skater A will accelerate further away because her mass is smaller - acceleration = force divided by mass. 

Stationary objects: The weight of the object pulls it down, whilst the e.g. table pushes it up - these forces are equal (the book is in equilibrium so doesn't move). Pairs of forces due to Newton's third law are: the normal contact forces from the table and book, and the book being pulled down by its weight due to gravity and it also pulling back up on the Earth.

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Momentum

  • (P) Momentum (kg m/s) = mass x velocity (m/s).
  • The total momentum before, is the same after the collision - known as conservation of momentum. Example: object A has no momentum and object P has momentum; when object P collides with A, object A now has the momentum whilst object P's velocity decreases and so loses momentum. The combined momentum of two objects = the original momentum of the object P. 
  • force = change in momentum (kg m/s) divided by time. If someone's momentum changes in a very fast time, the force will be very large and so it could be fatal. 
  • Conservation of momentum shows Newton's third law: when object P collides with object A, object A also exerts a force on P which causes object P to slow down once it hits object A. 

What affects your stopping distance (= thinking distance + braking distance): your reaction time - this is increased with tiredness, alcohol, drugs and distractions. Your speed - the faster you go, the further you will travel during your reaction time. 

Braking distance is affected by: your speed, the mass of the car, the conditions of the braks, how much friction there is between the distance and the road: you are more likely to skid if it is icy or your tyres are bald.

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Reaction Times + Stopping Safely

Ways of calculating reaction times: using a computer-based test (clicking colours) or you can use the ruler drop test by hoovering your hand over the 0cm mark of a ruler a someone dropping it. The longer the distance fallen, the longer the reaction time. You can use the uniform acceleration equation: final velocity2 - initial velocity2 = 2 x acceleration (which is 10m/s2 at free fall) x distance. Typical reaction time for this experiment is 0.2-0.6 seconds. An alert driver with have a reaction time of 1 sec. 

  • 30mph/13m/s: thinking distance (9m) + braking distance (14m)
  • 50mph/22m/s: thinking distance (15m) + braking distance (38m).
  • 70mph/31m/s: thinking distance (21m) + braking distance (75m).

Kinetic energy stores in car = work done by brakes

1/2 x mass x speed2 = braking force x braking distance

Estimations: A car's mass = 1000kg, a single decker bus = 10,000kg and a lorry: 30,000 kg. 

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Energy Stores

  • Kinetic, Gravitational potential, elastic potential, chemical (energy from chemical reactions), thermal, electrostatic, magnetic and nuclear (energy from atomic nuclei) energy stores. 
  • Change in GPE = change in height x mass x gravitational field strength (10n/kg on Earth).
  • Conservation of energy: energy can never be destroyed or created - it can only be stored, transferred between stores and dissipated. The total energy in a closed system has no net change. 
  • You can transfer energy: mechanically, electrically, by heating or by radiation. 
  • a ball rolling up a slope - it is doing work against the gravitational force so energy from the kinetic energy store is being transferred mechanically to it's gravitational potential energy stores.
  • a bat hitting a ball: energy from the kinetic energy stores of the bat are being transferred mechanically to the kinetic energy stores of the ball. Some energy is transferred mechanically to the bat and the ball (and to its surroundings). The rest is carried away by sound. 
  • rock dropping from cliff: Gravity does work on the rock, so the rock is constantly accelerating towards the ground. Energy is transferred mechanically from the gravitational energy stores of the rock to the kinetic energy stores of the rock.
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Efficiency

Efficiency = useful energy transferred by device / total energy supplied to device

Lubrication - to stop friction (which transfers energy mechanically to the thermal energy store of the object moving, which is then dissipated to its surroundings. You can lubricants such as liquids (like oil), so they can flow between objects easily and coat them.

Conduction - it transfers energy through an object - when one side of an object is heated, it will cause the particles that are being heated to vibrate and collide with each other - this transfers energy from their kinetic energy stores to other particles, which then vibrate faster. 

Products has thermal conductivity (how well a material transfers heat by conduction) - e.g. metal has a high conductivity whilst air has low conductivity. In a building, the lower the thermal conductivity of its walls, the slower it takes for the building to cool (the slower the rate of heat transferred through them). Some houses have cavity walls, made up of an inner and outer wall with an air gap in the middle. The air gap reduces the amount of energy (heat) transferring from the house because air has a low conductivity. Thicker walls help too, the thicker the wall, the slower the rate of energy transferred by conductivity.

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Energy Resource

  • Fossil fuels and nuclear energy are reliable - they have plenty of fuel that meets current demands, and power plants are always in stock. The cost is cheap and easy to build although nuclear power plants are expensive to build and decomission safely. Fossil fuels create environmental problems: they release carbon dioxide which adds to the greenhouse effect, burning coil and oil releases sulphur dioxide, which causes acid rain. To reduce this, take the sulphur out before burning the fuels. Oil spillages harm organisms. Nuclear power is clean but nuclear waste is dangerous and hard to dispose of - it's at risk of a catastrophe like the Fukushima disaster.
  • Bio-fuels advantages: carbon neutral (plant as many crops as they burn), grow quickly so different crops can grow all year round. Disadvantages: cannot respond to immediate demand (but to combat this, bio-fuels can be continuously produced and stored for when needed), expensive, not enough space or water for the high demand for crops that are grown for food, large areas of forest have to be cleared in some regions to make space for them which makes species lose their natural habitats. The decay or burning of this cleared vegetation produces carbon dioxide and methane emissions. 
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More Energy Resources

  • Wind power advantages: uses generator so wind turns blades and which turns generator and produces electricity, so no pollution, expensive but running costs are minimal. Disadvantages: lots are needed to produce as much power as e.g a power plant, they spoil the view for some people, they are loud, and only work when it is windy so can't respond to high demand.
  • Solar cells: material that uses energy transferred by light to create electric current. Advantages: no pollution, although expensive, running costs are low. Disadvantage:  they generate electricity on a small-scale, suitable for sunny countries and don't work at night. 
  • Dam and Flooding Valleys: rainwater is caught and allowed through the turbines. Advantages: no pollution , can respond immediately to high demands, expensive but low running costs and reliable. Disadvantages: huge impact of environment due to the flooding of a valley - many animal's homes are lost. 
  • Tidal Barrages: as tide comes in, it fills up the estaury. The water is then let out through turbines at a controlled speed to generate electricity. Advantages: no pollution, tides are reliable (they come twice a day), initial costs are high but there are no running costs. Disadvantages: affects boat access, spoil view, alter habitat (like wading birds), it doesn't work if tide is same height on both sides.
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Renewable

We are trying to increase the amount of renewable energy sources we use (the UK aims to use renewable energy resources to provide 15% of its yearly energy by 2020). Pressure from other countries and the public has meant that the governments have begun to introduce targets. This also puts pressure on energy providers to build new power plants using energy resources to make sure they don't lose money.

Car companies - electric cars and hybrid cars are already on the market and are increasing.

Disadvantages in general of renewable resources: expensive to build renewable power plants (smaller energy providers are reluctant to build this when fossil fuels are effective and cheap), many people might not want a wind farm which could lead to protests, some aren't reliable and can't respond immediately to high demand (wind power, bio-fuels), research into improving the reliability and costs of these takes time and money - this means we will have to continue using non-renewable power stations in the meantime and personal changes are very expensive because electric cars are expensive. 

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Waves

When a wave travels through a medium, the particles of the medium vibrate and transfer energy and information between each other - but the particles overall stay in place. 

For example, if you drop a twig in water, ripples form on, and move across the water's surface. The ripples don't carry the water (or the twig) away with them. 

If you strum a guitar string and create a sound wave, the sound wave is going to go in your ear but it doesn't carry the air from the guitar. 

  • Amplitude of wave - the displacement (movement) from the rest position to the crest or trough. 
  • Wavelength - full cycle of wave (e.g from crest to crest). 
  • Frequency - the number of complete cycles of a wave passing a certain point per second. 
  • Period - number of seconds it takes for one full cycle: 1/frequency. 

Transverse - the vibrations are perpendicular, these include: electromagnetic waves, s-waves, ripples.

Longitudinal - the vibrations are parallel to the direction the wave travels. Incluses sound waves and p-waves.

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Wave Speed

WAVE SPEED = FREQUENCY(Hz) x WAVELENGTH (m) 

WAVE SPEED = DISTANCE / TIME 

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Sound Waves

sound waves are caused by vibrating objects. Longitundal - pass through mediums in compressions and rarefactions. When sound waves hit (fastest in) solid objects, the air particles hitting the object, they cause the solid to vibrate back and forth. The particles hit the next particle in line and so on - passing all through the solid. Sound waves will be reflected by hard, flat surfaces - echoes.  Sound can't travel in space because it is a vacuum (no particles to move or vibrate).

How you hear sound: 

  • sound waves that reach the eardrum cause it to vibrate. These vibrations are passed on to tiny bones in your ears called ossicles, through the semicircular canals and to the cochlea. The cochlea then turn the vibrations into electrical signals. The brain interpret these signals as sounds of different volumes and pitches, depending on their frequency and intensity.
  • Human hearing is limited by the size and shape of our eardrum and the structure of all parts in the ear that vibrate to transmit the sound wave.
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Ultrasound

Ultrasound - higher than 20,000 Hz. Electrical devices can produce electrical oscilliations which can turn into mechanical vibrations and sound waves above 20,000hz (above human hearing).

Partial reflection - when some waves get reflected at the boundary between two medias whilst others get transmitted. Short bursts of ultrasound can be discovered as when a wave meets a boundary between two materials, the ultrasound will be reflected back. The time is takes for the reflection to reach a detector can be used to measure how far away a boundary is.

Medical imaging - Ultrasound wave pass through the body but then they reach the boundary between two medias (e.g. fluid in the womb and the skin of foetus some of the wave gets reflected back from both medias and detected - the timing and distribution of the echoes are processed in a computer to produce a video image of the foetus.

Ultrasounds can also be used to find flaws in materials - the cracks cause early reflections of ultrasound waves which can be detected.

Ultrasound is also used in echo sounding - which is a type of sonar used by boats and submarines to find out the distance between to the seabed or to locate objects in the water. 

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Infrasound

Infrasound waves - 20 Hz. Below human hearing. Elephants and whales communicate with this. By detecting infrasound, scientists are able to track these animals (for conservation purposes). 

Earthquakes produce seismic waves at a range of frequencies - we can detect these using seismometers. Seismologists work out the time it takes for the waves to reach each seismometer. When seismic waves reach a boundary between different layers inside the earth some are absorbed and some refracted. 

P-waves: longitudinal, they can travel through solids and liquids. They travel faster than S-waves.

S-waves: transverse, only travel through solids and slower than P-waves - can't travel through the outer core. 

Seismologists from the time taken for the waves to refract, are able to determined the Earth's internal structure.

Crust, mantle, outer core (liquid), inner core (solid).

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Reflection

angle of incidence (something moving in a straight line, like a light beam) = angle of reflection 

Total internal reflection: a wave hitting a surface can experience total internal reflection (when it is reflected back into the material). This only happens when a wave travels through a dense material towards a less dense material. 

This is when the angle of incidence is larger than the criticla angle for the particular material - every material has its own critical angle. 

Reflection - specular or diffuse: SPECULAR reflection is when waves are reflected in a single direction by a smooth surface - you get a clear reflection. DIFFUSE reflection happens when waves are reflected by a rough surface and in all different directions. This happens because the normal is different for each ray. When light is reflected by something rough, it will look matt and you don't get a clear reflection.

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Converging Lenses and Diverging

  • Converging lens (circular and is known as convex)  - this bring together light.
  • The principal focus of a converging lens is where the rays all meet (which is in front of the lens)
  • A real image is when the the rays come together to form an image - the image can be captures on a screen, because the light rays meet at the place where the image seems to be (for example, in front of you). Example: the image formed on the eye's retina. It is upside down. 

The axis of the lens is a line that passes through the middle. 

  • Diverging lens (known as concave) - spreads out light.
  • The principal focus of a diverging lens can be traced behind the lens where the rays of light all meet. 
  • A virtual image is when the light rays appear to be coming from a completely different place to where it actually is. The light rays don't actually come together to where the image seems to be, so it cannot be seen on a screen. Like a magnifying glass. 

You can increase the power of the lens (the more powerful the lens, the stronger it converges light, so the shorter the focal length. For converging, power is postive and diverging is negative. From certain materials like glass, you need to have a more strongly curved surface. 

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Diverging and Converging

Diverging lens always produce a virtual image. The image is the right way up, smaller than the object and on the same side of the lens as the object.

The distance from the lens to the objects affects the size and position of the image: an object two focal lengths from the lens produces a real, inverted (upside down) image the same size as the original object. 

An object between 1 focal length and 2 focal lengths produces a virtual image the right way up, bigger than the object and on the same side of the lens of the object. 

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Radio Waves

Transmiter - an object in which the charges inside it (electrons) oscillate to create radiowaves. The transmitted radiowaves are then absorbed by a receiver. The energy of the wavelength is absorbed by the receiver, causing the charges (electrons) inside the receiver to oscilliate. This creates an alternating current in the receiver if the circuit is complete. The current has the same frequency as the radio waves. 

Long-wave radio (wavelengths from 1-10km) can be received from half-way around the Earth because the long wavelengths bended around the curved surface. This make it possible for radio signals to be received even when the receiver is not in a line of sight.

Short wave radio signals (wavelengths of about 10m-100m) can be received at long distances. This is because they are reflected by the Earth's atmosphere. 

Bluetooth uses short-wave radio waves to send data over short distances between devices without wires (wireless headphones). 

For TVs and FM radio transmissions have very short wavelengths. To get reception, you must be in direct sight of the transmitter - the signal doesn't bend or travel far through buildings. 

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Microwaves

Communication two and from satellites (including satellite TV signals and phones) use EM waves such as microwaves are able to pass through the Earth's watery atmosphere. The waves are usually microwaves, but can also be high freqency radio waves too. 

For satellite TV, the signal from a transmitter is transmitted into space, picked up by the satellite receiver dish and then sent back to a different location, where ist is received by a satellite dish on the ground.

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Nuclear Radiation

If an outer electron absorbs enough radiation with enough energy, it can move so far that is leaves the atom. It is now a free electron and is said have been ionised. 

Nuclear Radiation:
Alpha Particles - helium nuclei, alpha radiation is emitted from the nucleus. They don't penetrate very far into materials and are stopped quickly. They can only travel a few cm in the air before being stopped. 

Beta Particles - beta-minus particles are fast-moving electrons released by the nucleus. Beta-plus particles are fast-moving prositrons. The postitron is the antiparticle of an electron. They are both moderately ionising - beta-minus particles have a range in air of a few metres and are absorbed by a sheet of aluminium (around 5 mm thick). Postitrons have a smaller range but when they hit an electron, the two destroy each other and produce gamma rays. - this is called annihilation.

Gamma rays - after the nucleus decays, it undergoes nuclear rearrangement and releases more energy. Gamma rays carry this energy away when released from the nucleus. They penetrate far into materials without being stopped and travel a long distance through air. This means they are weakly ionising becase they tend to pass through raher than collide although they do hit something. They are absorbed by thick sheets of lead or metres of concrete

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