Copernicus’s discovery that the Earth revolves around the sun was a huge shift in how we think about our place in the universe. Before this, it was widely believed that the Earth was the center of the universe. So, when Johannes Kepler proposed his three laws of planetary motion, which said that planets orbit the sun in elliptical orbits, it was a completely new way of thinking about the solar system.
The three Kepler Laws about the motion of planetary objects are as follows:
The orbit of a planet is an ellipse, with the Sun at one focus point.
A planet sweeps out equal areas in its orbit over equal periods.
The square of a planet's orbital period is proportional to the cube of its average distance from the Sun.
These laws explain the motion of planets in our Solar System. They also provide a foundation for understanding Newton's Laws of Motion, which govern the motion of all objects in the Universe.
In astrophysics, Kepler's laws serve as a base and hold a very prominent position. You may need to include this topic in your course contents if you are planning to teach an advanced physics course.
Image from Labster's Kepler Laws simulation.
Some students may find these three laws a bit tricky to understand. Read on to learn three reasons why Kepler's laws can be hard and five ways to teach them effectively.
Laws are abstract and their statements can be sometimes hard for students to digest. Here are three reasons why Kepler's laws can be hard for students.
Since this law explains the motion of celestial bodies, it seems abstract for students. As these bodies move in outer space; you cannot show them to the students. This makes it hard for them to visualize.
Kepler's laws apply to planetary motion and celestial bodies. Many students find it difficult to see how these laws are relevant to their everyday lives. They may wonder why they need to learn about something that seems so abstract and theoretical.
To understand Kepler's laws, students need to be comfortable with basic algebra and geometry. The equations can be complicated, and some students may find them difficult to follow.
Keeping in view some difficulties faced by students, here are five ways to make Kepler's Laws more approachable topic.
Laws can be quite boring for students and that’s because students think of them as a piece of information they have to memorize. However, to make things interesting and get them energized you can take start with a story. The story can be about the scientist who put forward this law or about an incident that led him to propose that conclusion. For instance, in this case, you can tell students about Tycho Brahe and Johannes Keppler.
Johannes Keppler though proposed the three laws but he would haven’t done without Tycho’s observational data. Tycho Brahe was a rich Danish astronomer with an extravagant laboratory in Denmark. He was from a noble family and therefore received thorough formal education. He was one of the last astronomers to work without a telescope. However, he had developed instruments to accurately take measurements, and his observational data was highly valued at that time.
Kepler was a German astronomer who unlike Brahe didn’t belong to any noble family. He was quite religious and a strong believer in Copernican theory. When Kepler was 27, he became an assistant to Brahe, who asked him to work on the orbit of Mars.
Brahe and Kepler had two different personalities and Brahe was much superior to Kepler. Initially, they had trouble working together. However, the sudden death of Brahe in 1601 proved to be a blessing in disguise for Kepler; he became an imperial Mathematician and got access to Brahe’s data. He struggled for the first two years with Brahe’s data, however, he got a breakthrough with these two laws. The third law was discovered a decade later.
There’s a long story on how Kepler led to the first laws; we have just presented a short version to describe how you can mention things from this perspective.
Sometimes it's difficult for students to understand things with technical terms. They seem new and their brains find it hard to understand the concept being conveyed through them. So, the best way to teach new theoretical laws is through analogies.
Analogies can be helpful when explaining difficult concepts. For instance, when introducing Kepler’s laws, you can say that the motion of celestial bodies is similar to the way a satellite orbits the Earth. Since the law explains the elliptical paths of space bodies, you can give examples of how elliptical orbits are found in nature, such as the way a leaf falls from a tree.
You can also help students become familiar with Kepler Laws by having them create models of the Solar System that demonstrate the laws in action. This can be done with balls of different sizes (to represent the different planets) and string (to represent their orbits). By moving the balls around and watching how they interact, students can gain a better understanding of how the laws work.
Physics laws usually describe natural phenomena or behavior of natural objects around us. In this case, the Kepler laws also mention the motion of celestial bodies. Now, it is not possible, even for diligent students to understand these laws without any visuals.
As an educator, you will need multiple clear and concise images to explain these laws. Here are a few figures, that you can use to explain each of the three laws.
Kepler’s first law states that the orbit of a planet is an ellipse, with the Sun at one focus point. (The elliptical path is just similar to a circular one, however, it’s a little stretched. )
In the figure, we can see that the path of all planets around the Sun is elliptical. But the eccentricity of this path is too small, that we confuse it with a circle.
Figure from Labster explaining Kepler’s First Law
The second law states that each planet sweeps out equal areas in its orbit over equal periods. This law explains the fact that a planet doesn’t move at the same speed all the time. When it is closer to the sun, it moves faster, as shown by the arc length in Area 1. But when it is away from Sun, it moves slower, as shown by the arc length of Area 2.
If you look closely at the figure, you will see that planet has covered more distance in the first case, and less distance in the second case, during one month period. However, in the first case, the orbit is narrow, while in the second case, it's wider. So, the total area, despite speed variations, is the same in each case.
The third law explains the relative motion of planets with respect to each other. The law states that the square of a planet's orbital period is proportional to the cube of its average distance from the Sun. In similar terms, it means that planets that are far from the Sun will take a longer time to complete their orbit around and vice versa.
In the figure below, you can see that the closest planet completes more than three-fourths of its orbit in one period, whereas the end planet just covers a fractional distance after one time period.
In addition to these figures, you can also use animations to explain the path of planets and their orbits. For instance, the animation below shows the orbit of a planet around the Sun.
Image from Labster's Kepler Laws simulation.
Keppler’s laws are used in many fields, from astronomy to engineering. Mentioning how these laws are used in the real world can help students see their relevance.
Motion of Satellites
Kepler's laws are greatly applied to study the motion of planets, asteroids, and other space objects in the solar system. Today, they are being used to design and launch satellites in space.
Newton got the idea from the Kepler laws and put forward his own three laws on motion and universal gravitation law. These laws are the base of modern physics.
Kepler’s laws explain the movement of celestial and space bodies, which cannot be physically shown to students nor you can design any experiments around these laws. In this case, Labster virtual lab simulations can help you.
At Labster, we create interactive simulations based on real-world scenarios to explain complex scientific phenomena. Students play games, make fun and learn through their interaction during the simulation.
For the current case, you can check out Kepler Laws simulation, in which students get in search of life on other planets. Along the journey, they learn about the shape, and path of planets’ orbits and how their velocities change along an orbit.
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