SPEAK OUR LANGUAGE

• CELL – Core Experience Learning Lab
• SDR – Scientist Data Record

ASK WHY

Great scientists question the world around them. We encourage our LabLearner students to do the same. In anticipation of this, we explain the importance of learning the concepts in the Ask Why section within the CELL. Our hope is that these explanations help students understand why science matters.

BRANCH OUT

Each Investigation introduces students to a different branch of science or STEM (Science, Technology, Engineering, Mathematics) career that utilizes the scientific concepts of the CELL. These real-world connections will help students see the relevance of what they are learning. STEM connections are also integrated into each Performance Assessment.

GET FOCUSED

The Focus Questions in each Investigation are designed to help teachers and students focus on the important concepts. By the end of the CELL, students should be able to answer the following questions:

Investigation 1:

• What causes the changes in day and night on the Earth? The movement of the Earth as it rotates on its axis causes different parts of the Earth to be turned toward the Sun, which causes day, and away from the Sun, which causes night.

• What causes the change in seasons in the Northern and Southern Hemispheres? The tilt of the Earth alters how directly the light shines on the Earth during different points in its revolution. This causes some areas of the Earth to experience seasonal changes.

Investigation 2:

• Based on your model, why do you think we observe different phases of the Moon from the Earth? The position of the Sun, Earth, and Moon cause the phases of the moon.

Investigation 3:

• What causes the orbit of the planets around the Sun and the Moon around the Earth? The combination of forward motion and gravity causes the planets to orbit the Sun and the Moon to orbit the Earth.

Note: The Focus Question for Investigation Three and Four is the same. Students continue to explore the orbit of the planets through both investigations.

Investigation 4:

• What causes the orbit of the planets around the Sun and the Moon around the Earth? Why are they important in maintaining the orbit of the planets and the Moon? The combination of forward motion and gravity causes the planets to orbit the Sun and the Moon to orbit the Earth. Without this precise amount of gravity, planets would either fly out of orbit in a straight line or they would be pulled toward the Sun.

Note: These are succinct responses to the Focus Questions and are placed here for easy reference. Fully developed responses to the Focus Questions can be found on each PostLab page.

Note: Some questions may be revisited as the CELL progresses. As students acquire additional knowledge, their responses should reflect this.

LEARN THE LabLearner LINGO

The following list includes Key Terms that the teacher should introduce, as appropriate, within the CELL. These terms should be used, as appropriate, by teachers and students during everyday classroom discourse.

Note: Additional words may be bolded within the Backgrounds. These words are not Key Terms and are strictly emphasized for exposure at this time.

Investigation 1:

• Rotation: the turning of a planet on its axis
• Orbit: the pathway of an object around another, such as the Moon around the Earth or the planets around the Sun

Investigation 2:

• Revolution: the movement of a planet or Moon around another body, such as the Sun or a planet

Investigation 3:

• Gravitational force: the force that exists between all objects because of their mass. The force of gravity acts to pull objects together.

Investigation 4:

• Newton’s First Law of Motion: a scientific principle first described by Sir Isaac Newton, which states that an object in a state of uniform motion stays in that state unless acted upon by an outside force.
• Force: a kind of a push or a pull on an object. A force causes an object to accelerate in the direction of the force.

BE PREPARED

An overview of the materials for each lab is placed here for easy reference. Specific teacher preparation for the labs is placed at the beginning of each Lab page.

EXTEND YOUR THINKING

The following information is included so that teachers have additional background knowledge pertaining to the concepts introduced in the CELL. Teachers may choose to use this information enrich students during instruction, but this is optional and not necessary for the intended students’ learning outcomes.

In the earliest recorded history of humans, we see evidence of their wonder and amazement at the Sun, the Moon, and the stars. Today, most people take it for granted that the Earth is round and orbits the Sun, while the Moon orbits the Earth. But, even though Newton explained the motion of the planets over 300 years ago the majority of people today do not understand what causes the orbits of planets, night and day, the phases of the moon, or the seasons. When asked many people report misconceptions such as the Earth’s shadow causes the phases of the Moon or the seasons occur because of the changing distance from the Sun. The goal of this Core Experience Learning Lab is to provide the students with the correct conceptions about planetary motion through models and simulations.

Until relatively recently during human history, our human-centric view of the Universe was that everything revolved around the Earth (e.g., Ptolemy). Instead, Copernicus recognized that the planets revolve around the Sun. By recognizing that the Earth is approximately spherical, rotating while revolving around the Sun, and the Moon also approximates a sphere that rotates around the Earth, we can begin to understand concepts behind the calendar. We can understand a year as the time it takes for the Earth to complete one orbit of the Sun. A day occurs as the time for the Earth to rotate once, with daytime occurring while we face the Sun and night being the time we face away from the Sun. Therefore half the world experiences night, while the other half experiences day. The lunar cycle is approximately 28 days which is similar to the length of a calendar month.

The most common misconception of the cause of the seasons is the changing distance of the Earth from the Sun. This theory is based on the notion of an extremely elliptical orbit around the Sun and can be discounted for two reasons. Firstly, if the seasons are caused by distance from the Sun, then the seasons would occur at the same time for the whole of the Earth, however, we know that when it is winter in the Northern hemisphere it is summer in the Southern hemisphere. Secondly, while the Earth’s orbit is an ellipse it approximates a circle with its largest diameter less than 5% greater than the smallest diameter. This difference is not enough to cause the seasons. The seasons stem from the tilt of the Earth which leads to a change in the directness of the Suns rays hitting the Earth. During the summer, the path of the sunlight is more direct and is least direct during the winter. This explanation for the seasons is demonstrated in Investigation One.

A common misconception of the lunar cycle is that it occurs due to the Earth’s shadow on the Moon. However, the simulation in Investigation Two demonstrates the phases of the Moon occur because of the proportion of the Moon that we see from Earth as illuminated by the Sun (Figure 1). For example, the Sun illuminates half of the Moon, but when the Moon is beside the Earth we only see part of the side of the Moon that is illuminated. In addition to understanding the causes of night and day, the seasons and the phases of the moon students also need to know what causes the motion of the Earth, Moon, and other planets.

Investigations Three and Four are designed to help students to comprehend the causes of planetary motion (Figure 2). Circular (e.g., planetary) motion occurs because of two things. Firstly, an object (e.g., planet) is already moving with a certain speed in a particular direction (i.e., constant velocity). Secondly, a linear force (e.g., gravity) acts on the object (e.g., planet). The force of gravity causes the Earth to accelerate (speed up) in a straight line towards the Sun. This occurs due to Newton’s second law known as the law of acceleration, which states that the force on an object is linearly proportional to the mass of the object and its acceleration (see equations below).

In other words, a net force causes an object with a mass to accelerate. If the Earth was not moving to begin with, the force of gravity would cause the Earth to accelerate until it collided with the Sun.

The reason that the Earth and Sun do not collide is that the Earth has a linear motion in a straight line parallel to the Sun. It is this combination of the Earth’s linear motion and the acceleration toward the Sun (sideways to the linear motion) which leads to a curved trajectory, and ultimately an orbit, around the Sun. To see that this linear motion is important in circular motion we simulate what would happen if the force of gravity was turned off. If the force of gravity between the Earth and the Sun was turned off, the Earth would move in a straight line (at a tangent from its orbit) at a constant speed. The Earth would not continue to move in a curved path. This is simulated in Investigation Three by letting go of the rope or hand which represents the gravitational force of the Sun. Also, in Investigation Four when the string is let go (gravity is turned off) the ping pong ball travels in a straight line through the flour. This observation is explained by Newton’s first law, the law of inertia, which states that an object will remain at rest or move with a constant velocity (i.e., constant speed in a straight line) unless acted upon by an external force.

This model of the Earth and Sun which includes only two factors, the force of gravity and linear motion, explains the motion of all the planets. In fact, the orbit of the Moon around the Earth is also explained by the Moon’s linear motion and the force of gravity between the Earth and the Moon. The success of Newton’s laws is that they not only explain planetary motion but also the motion of objects on Earth. If you drop a basketball it accelerates towards the ground until it collides with the ground. If you roll the basketball off a table it now has linear motion parallel to the force of gravity so that it moves forward and accelerates towards the ground. What happens if you roll the ball faster off the table? Yes, the ball covers a larger horizontal distance due to its velocity (linear speed) before impacting the ground. Now imagine that you could roll the ball fast enough so that its fall towards the ground exactly matches the curvature of the Earth. At this point, the ball will continue to orbit the Earth (neglecting other forces). This is exactly what happens to an artificial satellite in orbit around the Earth!

This Core Experience Learning Lab helps students to understand the causes behind our everyday experience of night and day, the seasons, and the phases of the moon. It also explains the two factors causing planetary motion, which are gravity and linear motion. Through understanding planetary motion, which is an example of circular motion, we introduce students to Newton’s first and second laws of motion.