This investigation is great fun to do on a hot day! You will need a container to put water in – as large as possible. You can use a washing-up bowl, but if you can find something larger, so much the better. If you are lucky enough to be able to set up a paddling pool, you’ll be able to cool off after all your hard work……
This is a large, shallow box that I usually use for storing paper. It’s best if you can put it on a table, but there are ways round having to keep it on the floor.
Cut four equal strips of cardboard (I save boxes used for deliveries). These are 14 cm by 4cm. If you are using a smaller tank (such as a washing-up bowl) you may want to cut smaller pieces (say 6 x 3 cm).
Cut one of the shapes to give a point. Make a hole, using a pencil, near the end of each piece. Join two pieces together with a length of thread – the thread should be about the same length as the water tank you are using. Join the other two pieces with a thread of the same length.
You are now going to test the two shapes – flat-end and pointy-end. To do this, they are going to be towed along the length of the tank. To make it a fair test, we want the towing forces to be equal, so we are going to use the other two shapes as weights – they should be the same weight as they are the same size. Pick up the two shapes that aren’t in the water (you can see them by the blue handle in the left hand picture) and drop them at the same time.
Which shape reaches the end of the tank first?
Here are some more shapes you can try.
Does it make a difference if the back of your boat is also shaped, rather than square?