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# Force

## Buoyancy – Galileo’s Thermometer

I am happy with the explanation in this video. I think students would need to draw free-body force diagrams to understand the physics behind the thermometer. In one of my assignments I asked my students to look up how the density of water changes with temperature. Then work out how much sand they would need to put into ping pong balls to get them to sink at a set of given temperatures, effectively creating their own Galilean thermometer.

## Spring Constants

The definition of the spring constant is the applied force per unit length of stretch of the spring. So for a constant applied force the spring with the largest spring constant will stretch the least distance i.e. the spring will be “stiffer”.

## Bed of Nails

I think the explanation in this video is ok but it might be interesting to mark out a space on the floor and pretend it is a bed of nails. Then get students to practice lying down on the “bed of nails” and standing up again. They fail if they double the pressure of their skin on the nails, e.g. sit in the bed, lie on their side, stand on the bed, put a hand on the nails that caries the weight of their body. Could be fun!

## Interrogating Formulae

Here again one of my tutors is advocating on the part of the students, this time with regard to formulas.

Many students have a simplistic view of what a formula can be used for. They see it as a ‘black box’ that turns given information into answers and if they choose the formula that the teacher is using, they will get the ‘right’ answer.