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# Speeding Up, Slowing Down

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### Speedy Sidney

### Illusion

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Age 11 to 14

Challenge Level

- Problem
- Getting Started
- Student Solutions
- Teachers' Resources

Try to approach the problem systematically.

As you go along try to understand why the graph takes the shape that it does:

- by relating it to the rolling polygon and the journey of the dot
- by trying to predict what will happen before you set the polygon rolling

Could the dot have been on the centre of a polygon?

Try for each of the polygons.

Could the dot have been on the centre of the base of a polygon?

Try for each of the polygons.

Could the dot have been on the centre of one of the sloping sides of a polygon?

Try for each of the polygons.

Could the dot have been on the centre of a side opposite the base of a polygon?

Try for each of the polygons.

Could the dot have been on a vertex opposite the base of a polygon?

Try for each of the polygons.

Could the dot have been on a vertex on the base of a polygon?

Try for each of the polygons...

Alternatively...

- try all possible positions of the dot in a triangle,
- and then in a square,
- and then in a pentagon,
- and then in a hexagon...

Two trains set off at the same time from each end of a single straight railway line. A very fast bee starts off in front of the first train and flies continuously back and forth between the two trains. How far does Sidney fly before he is squashed between the two trains?

A security camera, taking pictures each half a second, films a cyclist going by. In the film, the cyclist appears to go forward while the wheels appear to go backwards. Why?

How far have these students walked by the time the teacher's car reaches them after their bus broke down?