1.1. Party shops sell helium-filled balloons for various events. One such balloon is shown in Fig. 1.1.

Fig. 1.1

The ribbon is tied to a chair to stop the balloon floating away.

By modelling the balloon as a point mass, sketch a free body force diagram for the balloon and ribbon.

1.2. At its widest point, the balloon has a diameter 40 cm. The density of the surrounding air is 1.30 kg m^–3.

Calculate the upthrust on the balloon.

1.3. Balloons filled with air do not float.

Explain why a balloon filled with helium floats.