Unit 3: Considering the Influence of Light and Thermal Phenomena on Local Weathe
Unit 3: Considering the Influence of Light and Thermal Phenomena on Local Weather
V. Using Central Ideas to Explain Intriguing Phenomena Involving Local Weather at the Beach
Students in our area of the country can go to the beach on sunny days. The sand is warm; brrr, the water is cold! How can that be? Later in the day, however, the sky often clouds over and a breeze comes up from over the water. Why would that happen?
A. Considering the influence of the properties of materials on thermal effects
Question 3.8 Why is the sand warm and the water cool at the beach if the Sun has been shining on both in the same way for the same time?
- Use central ideas about the properties of sand and water, such as their thermal conductivities, specific heats, and reflectivities, to explain why the sand is hot and the water cool at the beach even though the Sun has been shining on them in the same way for the same time.
1. Example of student work explaining about hot sand and cool water at the beach
At a sunny day at the beach, the top of the sand is warm. The radiation from the Sun heats up the surface of the sand, but sand has a low thermal conductivity, so this energy stays at the surface of the sand. When you dig your feet into the sand it is cool below because the energy from the Sun was not transferred below the surface of the sand.
Water has a higher thermal conductivity, meaning the energy from the Sun is quickly transferred throughout the water, a big area. This means the heat will be even throughout the water, taking a lot more energy than is supplied to finally heat up the entire ocean. The water also feels cool because water has a bigger specific heat than sand. Despite the water receiving the same amount of energy for the same amount of time as the sand, the water needs more energy to change one gram of the water one degree Celsius. It takes 1 calorie of energy from the Sun to change one gram of the water one degree Celsius, while sand only needs 0.2 calories of energy from the Sun to change the same amount. This means it will take longer for the water to increase in temperature because water needs more energy to do so.
Another factor contributing to water temperature is the angle of the Sun. If the Sun is shining on the water from an angle, some of the light is reflected. When the light is reflected the energy is not being absorbed, so the temperature is not increasing as much. When the Sun is high in the sky above the water, the energy will be absorbed because the light is not being reflected.
Physics student, Spring 2016
B. Considering the influence of light and thermal effects on weather at the beach
A wonderful sunny day at the beach can turn cloudy and somewhat chilly with a breeze coming off the water late in the afternoon. What causes this shift in the weather?
Question 3.9 Why do clouds and sea breezes often form in the afternoon after a sunny day at the beach?
- Draw a diagram that illustrates why sand is warm, water cool, clouds often form