LEGO and M&M Half-Life

The half-life of a radioactive substance is the time it takes for the number of parent nuclei in a sample to halve, or for the count rate from the original substance to fall to half its initial level. Half-life is random and it is impossible to know which individual parent nucleus will be the next to decay. LEGO and M&Ms can be used to model this random decay while also negating the need for students to handle radioactive materials.

M&Ms

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Students start with 100 M&Ms (other sweets can be used so long as there are two distinct sides e.g. Skittles) and tip them into a tray. Record the number of M&Ms which have landed face-up (these represent parent nuclei which have decayed). Remove these ‘decayed’ nuclei and tip the remaining M&Ms into a second tray. Once again count the ones that have ‘decayed’ and repeat until all of the M&Ms have gone. Use the data to plot a half-life curve.

LEGO

Lego_Color_Bricks

Students throw 60 2×2 LEGO bricks into a tray and remove all of the bricks that land studs-up (these represent parent nuclei which have decayed). Stack these bricks together to show the activity i.e. the number of decays per throw. Throw the remaining LEGO bricks and again remove those that have ‘decayed.’ Stack these into a second column and place this next to the first to quite literally build an activity vs. throws bar chart. Repeat until all of the LEGO bricks have gone.

 

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Modelling Electric Circuits

Electricity is something that students encounter every day of their lives. However, there tend to be lots of misconceptions and these are best addressed at Key Stage 3 and GCSE by using models and analogies to explain what are otherwise abstract concepts.

Below are four methods of modelling electric circuits but it is important to remember that not all of them need to be used at once and that their value lies not only in students identifying the ways in which they work well but also in evaluating their limitations.

Hula hoop model

pink-hoop

Students sit in small groups (4-5 students) and hold a plastic hula hoop (or loop of rope) loosely in their hands. One of the students acts as the cell / power supply and begins to turn the hula hoop in one direction. The main message here is that the current moves at all points at all times in a circuit (a common misconception is that the current starts at the cell and slowly makes its way in procession through the wire).

The students will also feel some heat from the friction of the plastic hula hoop as it passes through their hands. This demonstrates that energy is being transferred but that the electrons themselves are not being used up (another common misconception). This model can also be used to introduce resistance i.e. for a given power supply, a higher resistance (i.e. a tighter grip on the hula hoop) will result in a lower current.

Student electron model

A student plays the part of the cell / power supply with a big plus sign on their right shoulder (positive terminal) and a big minus sign on their left (negative terminal). The remaining students are electrons and should arrange themselves in a tight circle (the circuit) around the edge of the classroom. Remind the students that electrons are negatively charged and, as such, repel each other (so they need to spread out evenly rather than clump together).

The student (electron) nearest the ‘positive terminal’ is pulled into the ‘cell’ and then pushed (gently!) out of the ‘negative terminal.’ As a result, this student will bump into / move close to the student standing next to the ‘negative terminal’ who, in turn, will be repelled and move away. This repulsion is repeated all the way around the classroom until a new ‘electron’ is pulled into the ‘cell’ at the ‘positive terminal.’ The whole process should be repeated and sped up to create a giant electric circuit.

Highlight that the push or shove from the ‘cell’ represents the voltage. The more powerful the cell, the bigger the voltage it gives to each electron. Finally, model resistance by placing two rows of chairs, through which the students have to squeeze, along one side of the classroom. As with the hula hoop model, the students should see that in a series circuit, if they are slowed down in just one small section of the circuit the current is reduced everywhere.

Bank and shop model

As above, the students should arrange themselves in a tight circle around the classroom. One student is the ‘bank’ (cell / power supply) and another is the ‘shop’ (bulb) which is located someway further down the road. At the bank, each student is given ten pounds (use Monopoly money) which they must then spend in full at the shop and therefore return to the bank with nothing (herein lies one limitation of the model as some energy is required for the current to get back to the battery).

monopoly

Next, pretend there are two bulbs in series of equal brightness or, in other words, two neighbouring shops in which each student spends an equal amount of money (the ‘bank’ should give each student ten pounds in two £5 notes in order to model this). Extend the activity by asking the students to model what would happen if there were two bulbs of different brightness or how the model would differ in a parallel circuit.

Mini whiteboards and sweets

Before building electric circuits, it can be useful for students to draw circuit diagrams on mini-whiteboards and then use sweets to demonstrate what is happening at each component. For example, if each sweet represents 1 V and the students are using a 6 V cell then they should start with just six sweets. If there are two bulbs in series but one is twice as bright as the other, how many sweets (volts) does each bulb require? Again, extend this activity by asking students to consider what would happen in different series and parallel circuits.

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Oreo Plate Tectonics and Moon Phases

A couple of nice activities using Oreo cookies (or in my case, cheaper alternatives).

Plate tectonics

Explain that the upper cookie is the lithosphere, the creamy filling is the asthenosphere, and the lower cookie is the lower mantle. Begin by simulating the motion of the rigid lithosphere plate over the softer asthenosphere by sliding the upper cookie over the cream. Then break the top cookie in half and simulate a divergent plate boundary by sliding the two cookie halves apart.

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Push one cookie half under the other to make a convergent plate boundary.

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Finally, simulate a transform plate boundary by sliding the two cookie halves past one another. Students should feel and hear that the two ‘plates’ do not glide smoothly past one another (thus modelling the earthquakes that occur at transform fault lines such as San Andreas).

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Moon phases

Simply remove the top cookie to reveal the creamy filling beneath. Scrape away and shape the cream to show the phases of the moon. Students should draw the relative location of the Earth and label the phases. Great as a revision tool or plenary.

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Forces Dance Mat

This is a great activity for introducing students to drawing force diagrams and resultant force. I have taken the idea directly from TES (the hugely popular original is available here) but I have made my own version in order to emphasise that the length of the arrow shows the size of the force. Obviously any music can be used to accompany it but I have always found that Gangnam Style works well (some of the students even do the dance moves as they jump about!).

Start the music, start the presentation and then jump in the direction of the resultant force. Have fun!

Motion Obstacle Course

I have just started the topic of Motion with my Year 9 students and used an obstacle course as an active way to introduce speed, distance and time equations.

obstacle course

The students set up an obstacle course in the sports hall (balance beams, hopscotch, cones, a wall to climb over etc.) Then, working in pairs, one member of each team tackled the course whilst the other timed them and recorded how long it took to complete each section. The students also recorded the length of each section using a measuring tape e.g. balance beam = 3m, hoops = 8m.

Now that the students knew the distance and the time taken, they could work out the speed at which they completed each obstacle. Finally, the students were asked to plot a distance-time graph (which lead nicely onto the follow-up lesson in which we looked at motion graphs using DynaKars).

Canva

Canva is a free online graphic design tool which can be used to make beautiful posters, infographics, presentations and many other things. It is extremely simple to use and features a vast library of templates, fonts and photographs to choose from.

My AS level biology students have recently used Canva to create eyecatching infographics summarising the structure and properties of biological molecules. I think they look great!