In this unit students are introduced to three force fields – magnetic, electric, and gravitational – and relates them to the bases upon which the theory of relativity was developed. This unit also explores the characteristics of good scientific theories and how they can be distinguished from pseudoscience suing fields and relativity as examples. First students map a magnetic field using a bar magnet and a compass to recognize that, while it is invisible, it can be measured and future observations predicted by using a scientific model of fields. Then they discuss the nature of an electric field by predicting the motion of a hypothetical test charge in an electric field. Next, the roles of mass and distance are explored in Newton’s Law of Universal Gravitation. Students observe the motion of a ball from a stationary position and while moving at a constant speed and then comparing these observations made when the observer is accelerating. These observations lead to a discussion of the importance of stating the frame of reference of the observer when making any observations. What follows from this is the concept of relativity in an inertial frame of reference. Next the role of the speed of light in the Theory of Special Relativity is explored using Einstein’s thought (or gedanken) experiments. Last, students explore the criteria for a scientific theory and contrast this with non-scientific or pseudoscientific claims. This latter discussion is particularly relevant in the Theory of Special Relativity where students’ concept of “common sense” is challenged.
STANDARD P1: INQUIRY, REFLECTION, AND SOCIAL IMPLICATIONS Students will understand the nature of science and demonstrate an ability to practice scientifi c reasoning by applying it to the design, execution, and evaluation of scientific investigations. Students will demonstrate their understanding that scientific knowledge is gathered through various forms of direct and indirect observations and the testing of this information by methods including, but not limited to, experimentation. They will be able to distinguish between types of scientific knowledge (e.g., hypotheses, laws, theories) and become aware of areas of active research in contrast to conclusions that are part of established scientific consensus. They will use their scientific knowledge to assess the costs, risks, and benefits of technological systems as they make personal choices and participate in public policy decisions. These insights will help them analyze the role science plays in society, technology, and potential career opportunities.
P1.1 Scientific Inquiry
P1.1D Identify patterns in data and relate them to theoretical models.
P1.1g Based on empirical evidence, explain and critique the reasoning used to draw a scientific conclusion or explanation.
P1.1i Distinguish between scientific explanations that are regarded as current scientific consensus and the emerging questions that active researchers investigate.
P1.2 Scientific Reflection and Social Implications
P1.2A Critique whether or not specific questions can be answered through scientific investigations.
P1.2h Describe the distinctions between scientific theories, laws, hypotheses, and observations.
P1.2i Explain the progression of ideas and explanations that lead to science theories that are part of the current scientific consensus or core knowledge.
P2.3x Frames of Reference
P2.3a Describe and compare the motion of an object using different reference frames.
STANDARD P3: FORCES AND MOTION Students identify interactions between objects either as being by direct contact (e.g., pushes or pulls, friction) or at a distance (e.g., gravity, electromagnetism), and to use forces to describe interactions between objects. They recognize that non-zero net forces always cause changes in motion (Newton’s fi rst law). These changes can be changes in speed, direction, or both. Students use Newton’s second law to summarize relationships among and solve problems involving net forces, masses, and changes in motion (using standard metric units). They explain that whenever one object exerts a force on another, a force equal in magnitude and opposite in direction is exerted back on it (Newton’s third law).
P3.1 Basic Forces in Nature
P3.1A Identify the force(s) acting between objects in “direct contact” or at a distance.
P3.1b Explain why scientists can ignore the gravitational force when measuring the net force between two electrons.
P3.1d Identify the basic forces in everyday interactions.
P3.6 Gravitational Interactions
P3.6B Predict how the gravitational force between objects changes when the distance between them changes.
P3.6d Calculate force, masses, or distance, given any three of these quantities, by applying the Law of Universal Gravitation, given the value of G.
P3.7A Predict how the electric force between charged objects varies when the distance between them and/or the magnitude of charges change.
P4.6 Electromagnetic Waves
P4.6C Explain why there is a delay between the time we send a radio message to astronauts on the moon and when they receive it.
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- What are the similarities and differences between magnetic, electric, and gravitational fields?
- What determines the magnitude of the gravitational force?
- What is an inertial frame of reference?
- How does the frame of reference of an observer affect observations?
- What criteria must a theory meet if it is to be accepted as a good scientific theory?
- What roles does the speed of light play in the Theory of Special Relativity?
frame of reference
inertial reference frame
inverse square law
Newton’s Law of Universal Gravitation
non-scientific (pseudoscientific) claim
speed of light
Theory of Special Relativity
thought (gedanken) experiment