Month: February 2014

The Weekend Experiments – Gravity

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Do you remember those days at school when your physics teacher would tell you that the strength of gravitational acceleration is 9.8 m/s2? You just took it on blind faith that that was the strength of gravity right? Well, in the first of my Weekend Experiments series we are going to look at a very simple experiment anyone can do to find the strength of gravity in their local area (or planet). All we need is some string, a weight and your mobile phone to do some timings and a few calculations.


Myself and students of St Saviours High School, Leribe, Lesotho performing the Pendulum Investigation – 2010

What you need

A long piece of string – the longer the better

Somewhere to hang it from

A stop watch – just use the one on your phone

A weight – even a small stone will do

And a measuring tape or metre stick

Calculator – again use the one on your phone if desperate

What you do

Tie the weight to the end of the string and hang the piece of string up from the other end (remember the longer the string the better).

Measure the length of the string in metres to the nearest mm if you can.

Let the weight rest down and give it a little push – just a few cm will do.

The weight should now start moving back and forth in a pendulum motion.

Using your stopwatch we need to time how long the pendulum takes to go back and forth (We call this an oscillation). Human beings don’t have great reaction times so I suggest you time 10 swings or more in one go and find an average.

The Calculation

So here comes the maths – don’t freak out.

g = L4π2/T2

L is the length of your string in metres

π is that circle thing equal to 3.142 (approximately)

T is the time taken for one swing

An example

L = 3.56m

T = 3.8 seconds

g = 3.56 x 4 x 3.142 x 3.142 / (3.8 x 3.8)

and I get..

g = 9.73m/s2

not a bad answer with just some basic equipment!



All your education are belong to us..

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1393060065639What should you do when parents have unrealistic expectations of their children? Recently at school the students received their IGCSE and AS level results. There was very large crowd outside of the principal’s office, crammed full even, with lots of expectant children and parents. Many of the students were being congratulated as they received their certificates and one of the girls fainted when she got her results. One parent asked me if I thought their child would get an A or B for their AS level but as that student only got a C grade at IGCSE, the level of expectation was simply way too high. It is always difficult to know what to tell a parent when they simply have too much expectation of what their son or daughter is capable of but the simple fact is students generally do not do better at AS level than IGCSE because the subject level is so much harder.

Recently I went to my own daughters parents evening. She has just started grade R. Some of the parents in the meeting wanted to know how quickly their child could be moved into grade 1. The principal quite rightly responded that with differentiation in the classroom that student would still be pushed and it is not necessarily wise to jump up a grade. One of the parents would not give up and was convinced that their little darling was a genius. The honest truth is that most children are just average at most things and with time develop specialist skills with positive feedback from parents and teachers playing an important guiding role. What’s the rush to get a child through high school? School is not just about grades and academics, perhaps more importantly it’s about social interaction, making friends, understanding how to interact with other people. Children should always be encouraged and supported throughout their education but over-expectation is dangerous, puts stress and pressure on the child and must be avoided at all costs.