# Loaded ship

for 11-14 14-16 16-19

In this activity, students make a model of a cargo ship and investigate how deep it sits in the water for different loads to predict when it will sink.

## Learning outcome

Students can use load and depth data to predict the maximum load a ship can carry.

## Preparation

Make a depth meter for each group by following the instructions on the template which can be downloaded below. You will need a laminator.

## Equipment

Each group of students will need:

- A depth meter
- A empty 1 litre cardboard drinks container (eg juice carton)
- A large tray or bowl with a depth at least 6 cm
- Access to tap water
- Scissors and sticky tape
- 5 x 50 g slotted masses (or 12 x 20 g masses)
- Paper towels (for spillages)
- A few drops of blue food colouring (optional)
- A ruler and graph paper

## Procedure

Ask students to:

- Fill the large container with water to a depth of at least 5 cm (adding the blue food dye if available).
- Draw a line around the bottom of the juice carton at a height of 5 cm from the base and cut along the line to make the ‘ship’.
- Stick the depth meter to the side of the ship ensuring that zero on the meter is aligned to the bottom of the ship.
- Place the empty ship in the container and record the depth in cm.
- Remove the ship and add a mass of 50 g.
- Lower the ship into the container and adjust the positions of the mass(es) so that the ship sits level in the water.
- Record the new depth in cm.
- Repeat the steps above to obtain data for cargo mass (g) and depth (cm) up to a depth of 4 cm.
- Plot a graph of cargo mass (g) against depth (cm).
- Use their graph to predict the maximum load that their ship can carry before sinking.

## Teaching notes

To aid with even loading of their ship students can use Blu-tack or a small strip of sticky tape to keep the masses in position. To predict the maximum load, they should draw a best line fit through their data and extrapolate to the height of their ship (5 cm).

The equation that describes the straight-line is:

M = ρAD – m

Where m is the mass of the empty ship, M is the cargo mass, A is the cross-sectional area of the bottom of the ship, D is the depth of the ship under water and ρ is the density of water.

## Extension (16-19)

Provide the above equation and rulers so students can determine A, and challenge them to work m and ρ from their graphs.