"Looking for shoeprints" Return to list of pracs

Aim: This activity is used to demonstrate investigating shoeprints.

Equipment: The equipment includes...  

• sandpit;
• watering can;
• metre ruler;
• heavy backpack.

Method: Make sure the sand in the sandpit is somewhat wet (to hold shape) and then rake it smooth. Walk slowly across the smooth sand. Measure the distance between the first 2 shoeprints. Also measure the depth at the heel and at the toe of a shoeprint. Record your result in a table. Also, record the shape of the footprint or any pattern on its sole. Repeat the procedure by running, jogging, or walking or running with a heavy backpack.

Making a plaster cast:

Equipment: The equipment includes...  

• plastic beaker;
• water;
• plaster of Paris;
• tray of soil;
• paperclips;
• glass beaker;
• plastic stirrer;
• strip of card (30cm x 5cm);
• measuring cylinder;
• brush.

Method: Put about 70mL of water in the plastic beaker. Fill the dry glass beaker with plaster of Paris. Make a shoeprint in the tray of soil and make a mould around the part of the shoeprint with a strip of card and a paperclip (eg. the heel only). Pour the plaster into the water and stir well until you have a thick, smooth cream. Pour it into the mould quickly and let it set for about 48 hours. Lift off the cast and rinse the cast under the tap and brush if necessary.

• Why is it important to was the plaster cast before examining?
• What effect does air bubbles in the plaster have on the cast?

Try to make a good plaster cast of: bicycle tyre; dog print on earth; scratches on a stone floor; car tyre tracks; marks on a bench top; etc.

Background knowledge: Marks such as shoeprints are often left at the scene of a crime. These can become important clues and evidence against a perpetrator can be found. Police often use plaster of Paris to make casts.