The Nature of Waves START-UP In this activity, you will observe the movement of a wave. Then, you will determine the source of the wave’s energy. 1. Tie one end of a piece of rope to the back of a chair. 2. Hold the other end in one hand, and stand away from the chair so that the rope is almost straight but is not pulled tight. 3. Move the rope up and down quickly to create a wave. Repeat this step several times. Record your observations. 1. In which direction does the wave move? 2. How does the movement of the rope compare with the movement of the wave? 3. Where does the energy of the wave come from? 1. In which direction does the wave move? The wave moves from one end of the rope to the other. 2. How does the movement of the rope compare with the movement of the wave? Each piece of rope moves up and down, that is, in a direction different from the wave. 3. Where does the energy of the wave come from? The energy of the wave comes from shaking the rope. When you stop shaking the rope, the wave eventually stops moving. Can you think of some examples of waves? Waves •Sound •Light •Water •Radio •Seismic. What is the function of a wave? A wave is a disturbance that carries energy from one place to another. A wave does NOT carry matter with it! It just moves the matter as it goes through it. A wave transmits energy from one place to another. For example, energy can be carried by a water wave generated by a boat out at sea to the shore, or by a sound wave from the loudspeaker to an audience’s ears. The most common waves found in daily life are water waves, sound waves and electromagnetic waves. Some waves do not need matter (called a “medium”) to be able to move (for example, through space).These are called electromagnetic waves (or EM waves). Some waves MUST have a medium in order to move. These are called mechanical waves. TYPES OF WAVES WAVES Mechanical waves Transverse waves Electromagnetic waves Longitudinal waves Transverse waves Mechanical Waves Require matter to travel through The matter the mechanical wave travels through is called a MEDIUM Examples of a medium that a mechanical wave can travel through: sound waves, earthquake waves, water waves Electromagnetic waves Energy transfer without going through a medium. Examples include: Microwaves, Visible light, TV and radio signals, and X rays Although electromagnetic waves do not need a medium, they can go through matter, such as air, water, and glass. The energy that reaches Earth from the sun comes through electromagnetic waves, which go through space. Wave Types Mechanical Electromagnetic e.g. Water waves, waves on a e.g. Radio, X-Rays, Light rope, sound Must have a substance to travel through Does not need a substance to travel through but can travel through various substances Cannot travel in a vacuum Can travel in a vacuum Vibrations passed on from molecule to molecule Travel at very fast speed in a vacuum: 3 × 108 m/s Quiz 1. A wave is a disturbance that travels through _____ or (space, matter) _____. (energy) 2. A wave carries _____. 3. Waves that require a medium are called (mechanical) _________waves. 4. Waves that do not require a medium are called (electromagnetic) ____________________waves. • All waves transfer energy by repeated vibrations. • Based on the direction in which the particles of the medium vibrate compared with the direction in which the waves move. • The two main types of waves are transverse waves and longitudinal waves. A part of a longitudinal wave where the particles are crowded together is called a compression. A part where the particles are spread apart is a rarefaction