around a comer. Aside from travelling in a straight line, light also travels in all directions. It can travel very fast. Mediums like air, water and a book, a wood or a plastic chair or a wall can block the light. transparent glass slow down the speed of light. Materials like a cardboard, Activity 2: "How does sound travel?" What you need: A ticking clock Balloon filled with water Wooden door What to do: 1. Cover one ear. Hold the clock 5cm away from your ear. Can you hear the clock ticking? 2. Place the water-filled balloon against your ear. Hold the clock against the balloon. Can you hear the clock ticking? Figure 2. A boy trying to hear the ticking sound of the clock. 3. Place your ear against a wooden door and the clock on the other side while covering your other ear. Can you hear the clock ticking? Guide Question: 1. In which material did you hear the sound of the ticking clock best t? Why?​