Projectile Motion using Angry Birds

Used Tracker motion analysis today to help us understand more about how projectile motion works. The video below shows how to use the autotracker function to analyse the motion of the Angry Bird.



We used the analysis to figure out how the horizontal and vertical motion of the bird changed over time. We also calculated the approximate length of Angry Bird required to give an acceleration similar to gravity. The question sheet below was used as a guide.

Projectile Motion Using Angry Birds

Projectiles

We started off with the simplest type of projectile - those that are projected horizontally. They therefore have an initial vertical velocity of zero so are pretty much the same as our calculations on bouncing balls and the like.



Things get a little more complicated when you launch projectiles into the air at an angle because the initial vertical velocity is no longer zero. If this is the case then you must think about the horizontal velocity and the vertical velocity separately.

5D - Vectors and vector diagrams

We draw vector diagrams to simulate what we see in the real world. I think some people still don't get this.

As I see it, there are two main rules when drawing vector diagrams:

1. Join your vectors 'tip to tail'
2. Use your common sense!

If the resulting velocity, displacement or force looks wrong then use your common sense. Th diagram is only showing you what will happen if you put these two velocities together or these two forces together.

5D - Errors and Uncertainties 2

When we have more than one uncertainty to deal with, we need to choose which one to take into account for our final answer. To do this, we use the value that has the greatest percentage uncertainty.

The percentage uncertainty is expressed as a percentage whereas the absolute uncertainty is written as a number.

5D - Errors and uncertainties

There are three types of uncertainty we need to consider for Higher Physics:

• Reading; occurs when taking a measurement visually
• Random; the subtle differences between experiments that produce differing results are caused by random errors
• and Systematic; when there is something wrong with the equipment or the way in which it is used.

We can limit the effect of random errors by carrying out repeated measurments. You need to know how to calculate the mean and the error in the mean (approximate random uncertainty).

4H - Radiation types

Learning outcome: 

•We are learning what radiation is and its different types.

Success criteria: 

•Be able to describe the effects that radiation can have 

•Be able to give examples of sources of radiation

•Be able to give at least one method of detecting radiation

•Be able to describe the different types of radiation and how to protect ourselves against them

4H - X-rays

Learning outcome:  We are learning how x-rays work and how they can be used to diagnose health problems

Success Criteria: 

•Be able to describe one use for x-rays in medicine

•Be able to describe how x-rays can be detected

•Be able to describe how x-rays behave when they enter the human body

•Be able to describe the advantages of computerised tomography (CAT scan)

 

2.4 - Collecting volcanic ash

This week we set about collecting some of the volcanic ash from the recent Grimsvotn eruption. We collected this data as part of a British Geological Survey project to track the spread and concentration of the ash cloud.

We used sellotape and old catalogues atop a Land Rover in the car park; leaving these out for the entire school day on Tuesday. Thereafter, we attached the tape to the back of a sheet of paper which we will send to the British Geological survey for analysis.

Hopefully we'll have picked up some ash throughout the day. Pretty amazing when you think that it has travelled around 1000 miles to get to where we are.

How to make a webcam into an infrared camera

Every time I teach about infrared radiation, I have a lot of nice images I can show my classes and maybe even a clip or two from 'The Predator' to go with them. I saw an email today offering an infrared camera as part of your attendance on a course and it reminded me of the fact that I have always wanted one to show realtime images in the infrared spectrum.

Given that I've got a little more time on my hands than I normally do, on account of it being the exam season, I set about trying to make myself one.

I opened up the nearest webcam and screwed off the plastic section surrounding the lens. On the back of it and found the infrared filter.











I duly removed it and replaced the infrared filter and set about replacing it with a visible light one. I initially cut a small square from some blackened x-ray film and tested it but I was still seeing some colour. This guide  suggested that the best visible light filter could be scavenged from the negatives of some old colour film.


This was the trickiest part of the process but I eventually managed to fit two small pieces of this film in place on the back of the lens.


I've tested it briefly and it looks pretty good. I'll post some images later.

My camera was a basic Creative Live Cam but other manufacturers should be constructed in a similar fashion. A nice cheap alternative for bringing infrared into the classroom!

5CH - Past papers by topic

Now uploaded for the whole course. All of you should be working through these over the holiday, picking out the topics you find most difficult in the first instance. Any problems, give me a shout.

5CH - MOSFETs

Look at the last device which uses p-type and n-type materials to conduct - the MOSFET. It will only switch on if there is a sufficient voltage across the gate of the transistor.

5CH - P-n junctions

By putting some n-type and p-type materials together you can make all sorts of wonderful devices. Diodes, LED's, solar cells and LDR's all rely upon the technology of semiconductors. We explained how each of these devices work in terms of electrons and holes. You need to be able to distinguish between reverse bias and forward bias as well as photovoltaic mode and photoconductive mode.

5CH - Semiconductors

Started semiconductors today. Semiconductors are, as the name suggests, materials that 'sort of' conduct electricity. We can add impurities to an element - the process is called doping - which allows the electrons to move. This can be done by adding an element with an extra electron (n-type) or by adding an element with one less electron (p-type).

5CH - The Bohr model of the atom

Did more work on the Bohr model today. Energy is taken in by the electron to jump up one level or more and energy is given out in the form of a photon as the electron moves back down to its original level. The energy required to move from one level to the next can be displayed in an energy diagram. The bigger the gap between the lines, the more energy it takes to move between the levels. These energies are always shown as negative with the ionisation level (where the electron leaves the atom) being at 0 Joules.

5CH - Quantum theory of light

If light and other electromagnetic radiations are made of photons then each photon must have an energy associated with it. This energy is E = hf. Thinking back to the photoelectric effect, we know that some materials will eject electrons when you shine radiation on them. The minimum energy required for this to happen is called the work function of the material. If a photon has an energy equal to this work function then it will cause an electron to be ejected to the surface. If the photon has an energy greater than the work function then the remaining energy will converted into kinetic energy of the photoelectron produced.

4H - Specific heat capacity (Homework out)

After carrying out an experiment to determine how well different metals heat up we related this to the idea of specific heat capacity. In simple terms this is a measure of how good a substance is at heating up or cooling down. This lead us to an equation for specific heat capacity and a few worked examples. Past paper on specific heat capacity for Tuesday.

5CH - Photoemissions

Photoemission is the release of electrons from a material. Whether an electron is released or not depends upon the frequency of the radiation hitting the material not the irradiance. This leads us to the idea that light and other types of electromagnetic radiation are made up of tiny particles called photons. The energy that these photons have is directly proportional to their frequency as stated in the the equation E = hf.

5CH - Irradiance

Irradiance is the power of radiation per unit area. The closer you are to a source of radiation, the greater the irradiance. As you move away from the source the irradiance will decrease, in other words there is less radiation per unit area. If you continue to move away from a radiation source then the irradiance will reduce as the square of the distance from the source. This means that if you double the distance from the source of radiation then the irradiance will be four times less.

5CH - Past papers by topic

Questions for Mechanics and Electricity. Radiation to follow.

You can download these or view them online.

5CH - Multiple slit diffraction grating

As we already know, a diffraction grating can be used to produce interference in the same way a double slit can. We looked at how we can use our knowledge of path difference with a bit of trigonometry to give us an equation for use with diffraction gratings. This gave us the equation nλ = d sinθ where n is the order of the maxima e.g. 1,2,3 etc. This equation can also be applied to the path difference for a minima but I haven't seen this asked for some time.

To calculate the slit separation, d,  you must know firstly how many lines there are per metre and then divide 1 by that value. The angle of deviation, θ, is the angle that the wave/ray is deviated from the normal line.

Remember also that wavelength of red light = 700 nm and wavelength of violet light = 400 nm.

5CH - Path difference

As we saw today, path difference is what causes interference. The path difference is the difference in distance travelled by the waves. This difference in distance will mean that the waves become either in phase or out of phase. Waves that arrive in phase will interfere constructively and waves that arrive out of phase will interfere destructively.

We introduced two equations for working with path difference, one for maxima and one for minima. You need to be able to select the correct one for the given situation. Remember of course that the path difference equation for a minima isn't actually very useful! It might be best to use p.d. = (n - 1/2)λ.

This will not be given in the data booklet though.

5CH - Interference of light

Light can undergo interference as well. You can use a diffraction grating to make this happen. You need to be able to explain an interference pattern of bright and dark areas, you also need to know the differences between white light through a prism and white light through a diffraction grating.

5CH - Interference

Looked at interference today. Interference is caused by two or more waves getting in each others way. When they meet they produce either constructive or destructive interference. What these are is explained in the video. All wave types - sound, light etc. exhibit interference patterns which are made up of alternating lines of constructive and destructive interference.

5CH - Ray diagrams

Applied the refraction formula to drawing/completing ray diagrams today. You can use the refractive index formula along with the knowledge that the angles in a triangle add up to 180 degrees to figure out how light will pass through most objects.

Sometimes we will have to consider the critical angle when completing ray diagrams. If the angle of incidence is greater than the critical angle then the light will reflect. The angle of reflection in these cases is equal to the angle of incidence.

Note: The more observant will spot my mistake with the angles. They should be 54 and 36 not 34 and 56. Final answer is still correct.

5CH - Critical angle and internal reflection

Not all light will be refracted through materials such as glass. Materials like glass have the ability to internally reflect light if the ray is at a certain angle. This is called the critical angle and is the angle beyond which no refraction will take place. In other words, the light will not pass through the material but be reflected back in the original direction of the ray.

Remember that at the precise point of the critical angle, the ray of light refracts into the air at 90 degrees. This is the last refraction that occurs before all light is reflected. Recall also that the angle of incidence is always equal to the angle of reflection.

5CH - Refraction past papers

Practised using the extended refraction formula today. There are three things that change when light enters a more dense material - the direction (angle), the wavelength and the speed. This is reflected in the equation we used today. Remember the more dense medium goes on the bottom of the equation for all values.

Also need to know the differences between blue and red light. Red light refracts less than blue because blue light has a greater refractive index.

5CH - Extended refraction formula

Extended the refraction formula today to include wavelength and velocity. When light moves into a more dense medium, it slows down. Its wavelength also decreases. We can use these changes in velocity and wavelength to calculate refractive index, n.

We also looked at white light refracting through a prism. Red refracts least and violet refracts the most. Because the angles of refraction for the colours that make up white light are different, then it must mean they have different wavelengths and different speeds as they enter the prism. This leads us to the idea that different colours of light have different refractive indexes.

5CH - Refraction

Finished the first lesson on refraction today. It is the refractive index (n) that determines how much refraction occurs. This is expressed as a number with no units. We proved the equation for this and looked at the couple of different ways that the equation can be written. It is very important to make sure that the angle in the least dense medium is 'on the top' of the equation. This is the only way that the refractive index will always be greater than 1.

5CH - Waves

Finished our introduction to waves today. There are two types of wave, most of the ones we will encounter are transverse waves. Frequency, period, amplitude and wavelength should be well understood from Standard Grade.

The various experiments and examples that we will cover in the coming weeks will often refer to 'rays' and 'wavefronts'. Make sure you are okay with these before we move on.

4H - Nuclear power

Nuclear power stations use nuclear fission to generate the heat energy to produce electricity. Neutrons are fired at uranium nuclei causing them to break apart and release energy. This process is called a chain reaction and produces the heat that is used to turn water into steam and drive the turbine that connects to the generator to make electricity.

The main advantage of nuclear fuel is that it produces far more energy than coal, oil or gas. But there are a lot of misconceptions about nuclear power and many people mistrust it, primarily because of its history. The Chernobyl disaster is probably the main reason for this and we'll spend a bit of time looking at this and what caused it to happen.

4H - Generation of electricity

Covered how electricity is generated by using coal, oil and gas. They all work in the same way by using the heat given off by the fuel as it is burned to change water into steam and turn the turbine to generate electricity.

Also looked at hydroelectric power stations as well. They use water released from a height to turn a turbine and generate electricity. A pumped storage hydroelectric power station uses the same technique. Water is pumped back to the reservoir, usually at night when the energy demand is low. The water is then released to help 'boost' the amount of energy available at peak usage times.

3H - Cost of electricity

Having already established that the kilowatt-hour is the unit of energy that we use to pay for our electricity, we went through how to calculate the cost of electricity used. This can be a bit confusing because we have to convert our power rating to kilowatts and our time to hours - this is really the opposite of what we normally do.

There are two types of calculation; the first is just an E=Pt calculation which we have done before but we have to use kilowatts instead of Watts and hours instead of seconds. If we do use Watts and seconds we'll get the answer in Joules which will be a really big number! The second type of calculation is where the cost is taken into account. Here all you do is multiply the number of units (this is the same as saying the number of kilowatt hours) by the price per unit which will always be given in the question.

Star Count Week 2011

As part of the campaign for dark skies in the UK, the CPRE are looking for people to count the number of stars they can see in the constellation of Orion.

Orion is very prominent in the winter sky and can be found most easily by looking for the three stars in Orion's 'belt'.

They want as many people as possible to look to the skies this week and count the number of stars they can see in the above constellation. More information and how to submit your total here:

http://www.cpre.org.uk/campaigns/landscape/light-pollution/start-count-week-2011

I suggest some of you go out and try this, if nothing else it'll help you find your way around the night sky!

3H - Parallel resistance calculations

Having proved the equation for parallel resistance, we looked at the three ways that we can tackle these types of calculations.

3H - Resistance in parallel

Proved the resistance in parallel equation today. A bit more complicated than the total resistance formula for a series circuit where we can just simply add the values together. The experiment showed that the total resistance in a parallel circuit actually decreases as we add more resistors so a new equation is needed. We'll do some examples with this equation next week.

5CH - 2007 Q27 Op amps

Solution to another Higher paper question with the differential op amp as a monitoring circuit. Some of you struggled with (b) (ii) - we haven't covered MOSFETs in class yet but you should still be able to figure out how changing the value of one resistor affects the potential at the points in a wheatstone bridge.

In this example, changing Rth causes an increase in the voltage across Rth. This means that resistor Z has less of a voltage across it and therefore there is less of a voltage a point Q.

5CH - Differential amplifiers as a monitoring circuit

The differential amplifier can be used to monitor changes in heat or light etc. The example we looked at was a temperature monitoring circuit. A wheatstone bridge is used to control V2-V1 and the output of the amplifier is connected to a suitable output device.



Some of you struggled a bit with this question so have a watch at the solution and make sure you understand this type of question okay. It may look complicated but if you split the circuit into the three parts as mentioned in the previous video then it is easier to understand.

5CH - Differential mode op amp

More on differential op amps today. Proved the equation through experiment last week so moved on to work through some examples. Remember that Rf/R1 must equal R3/R2 for this equation to hold.

When you are identifying a differential mode amplifier, remember that it has two input resistors. Meaning that it has two input voltages. All the amplifier does is amplify this difference in voltage (make sure you know which is V2 and which is V1 as this might not always be given).

4H - Work done

Work done is the amount of energy given to an object to make it move in a certain direction. The amount amount of work done depends on the force applied and over what distance the force is applied for. These quantities are ties together in the equation Ew = Fd.

5CH - Square wave saturation

Went through inverting op amps with an ac input and showed via an oscilloscope that this setup can be used to produce a square wave. Also went through the solution to a past paper question on saturation.

5CH - Op amp saturation

Looked at saturation of op amps today. An op amp cannot produce an output voltage that is greater than the voltage of the supply. The output voltage will reach a maximum when the op amp saturates.

4H - Newton's Second Law

Newton's second law says that if an object has an unbalanced force applied to it then it will accelerate in the direction of that unbalanced force. The size of the acceleration depends upon the mass of the object. Objects that are bigger are harder to accelerate and more difficult to stop once they start moving. Smaller objects are easier to accelerate and easier to stop.

Remember that unbalanced forces cause accelerations and decelerations.

We worked on the second type of F = ma calculations today. These are when more than one force is given so it necessary to calculate the unbalanced force first before using the equation.

Power, Energy and Time

Each appliance has a power rating. This tells us how much energy it converts each second. We proved this relationship through experiment and worked through some examples with the E = Pt equation.

Inverting mode op amp

Talked about how to identify the inverting mode op amp today. Also proved the equation for an inverting amplifier through experiment and video contains a worked example using that equation.

Remember that the input resistor in inverting mode is connected to the negative (inverting) terminal. This resistor is R1 in the equation. Rf is the feedback resistor that 'loops' back from the output to the input. It is these resistors that determine the gain that the amplifier has i.e. how much it will increase the input voltage by.

An inverting amplifier not only changes the size of the input voltage but also changes (inverts) the sign. So a positive input will give a negative output and a negative input will give a positive output.

2007 Q26 Capacitance

The solution from today's past paper on capacitance. Some of you are still struggling with resistors in capacitive circuits. Remember that at the moment when the switch in such a circuit is closed, the capacitor is fully discharged so all the voltage of the supply is across the resistor and the current in the resistor is at a maximum. This current can also be called the charging current.

Unless the capacitor is fully charged or fully discharged then the resistor and the capacitor will each have a share of the voltage. Always read the question carefully so that you know whether the stated voltage is across the capacitor or the resistor.