![]() I ask the class: "Does this mean that every runner did a false start? What explains this?" We see the runners begin to run before we hear the starters pistol. To have students think about how the speed of light compares to the speed of sound, I show a video, False Start, where a camera is positioned over 200 meters from the start line of a race. CCSS Math Practice 1: Make sense of problems and persevere in solving them is also applicable for this activity as students first must understand the problem and then create an analogy that makes sense. It is in the context of performance standard HS-PS4-1: Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media. This applies NGSS Science Practice 1: Asking questions (for science) and defining problems (for engineering), Science Practice 5: Using mathematics and computational thinking, Science Practice 6: Constructing explanations (for science) and designing solutions (for engineering) and Science Practice 8: Obtaining, evaluating, and communicating information. They research various quantities and develop an analogy along the lines of the speed of light is to the speed of sound as x is to y. This is tough to grasp without some kind of analogy, so students spend this period to create one. The truth is, in the Earth's atmosphere the speed of light is about 800,000 times faster than the speed of sound. There is a common misconception among people that the speed of light is relatively close to the speed of sound. Though we use wave speed throughout the unit, we have never directly explored the speed of light or how it compares to the speed of sound in air. The speed of light is constant and does not depend on the speed of the light source.In lesson Wave Hello, students learned about the different wave properties, among them wave speed. Say that Einstein's bike travels at 10% the speed of light (30,000 km/sec): the speed of light from Einstein's headlight does NOT equal 330,000 km/sec. ![]() Light from a moving source also travels at 300,000 km/sec (186,000 miles/sec). Light from a stationary source travels at 300,000 km/sec (186,000 miles/sec). ![]() No matter how fast Einstein rides his bike, the light coming from his headlight always moves at the same speed. ![]() Although it might seem logical to add the speed of the light source and the speed of the light beam to determine the total speed, light does not work this way. The Special Theory of Relativity is based on Einstein's recognition that the speed of light does not change even when the source of the light moves. For example, beams of light from a lighthouse, from a speeding car's headlights and from the lights on a supersonic jet all travel at a constant rate as measured by all observers-despite differences in how fast the sources of these beams move. ![]() Instead, Einstein had an unexpected-and paradoxical-insight: that light from a moving source has the same velocity as light from a stationary source. Surprisingly, the answer has nothing to do with the actual speed of light, which is 300,000 kilometers per second (186,000 miles per second) through the "vacuum" of empty space. No matter how you measure it, the speed of light is always the same.Įinstein's crucial breakthrough about the nature of light, made in 1905, can be summed up in a deceptively simple statement: The speed of light is constant. ![]()
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