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Cross Cutting Concept-Cause and Effect: Look for evidence in a situation, provide an explanation (using your knowledge of forces, Newton's 1st and 3rd Law) for how forces affect the motion of the objects.
Science and Engineering Practices-Constructing Explanations (for science) and designing solutions (for engineering): Construct logically coherent explanations of phenomena that you observe. In the explanation, incorporate your current understanding of forces, Newton's 1st and 3rd Laws that are consistent with available evidence. Evaluate and critique competing design solutions based on a jointly developed and agreed-on design criteria.
Learning Objectives:
By the end of this unit, you should be able to.... (Those in bold will be essential & will be assessed formally in the curriculum)
1.
Be able to measure force using a spring scale accurately.
2.
Draw and interpret simple force diagrams (known as "Free Body Diagrams" or FBDs)
3.
Identify common forces (such as weight, normal force, friction...) acting on an object, and recall their properties.
4.
Know that a "force" is a vector an thus requires a magnitude (size) and direction. An arrow can be drawn to represent the vector.
5.
Know that the length of the arrow represents the size of the force and the direction of the arrow is the direction of the force.
6.
Use FBD to show forces acting on a system consisting of a pair of interacting objects. Calculate the net force acting on a system and between objects.
7.
Interpret and apply Newton's 3rd Law of Motion.
8.
Identify the action and reaction pair forces.
9.
Use a FBD to show the forces acting on an object and identify the reaction force.
10.
Interpret and apply the Newton's 1st Law of Motion.
11.
Distinguish qualitatively between static and kinetic friction, and describe their effects on motion of objects.
(Adapted from Minds on Physics Activity #50: Recognizing and Interpreting Free-Body Diagrams)
A free-body diagram shows all the forces acting on a single, isolated body.
Only forces should be entered on a free-body diagram.
The body must be isolated ( a free body.)
Indicating all of the forces acting on a single body makes it possible to discuss and determine the behavior of that body without referring to any of the objects exerting the forces.
When drawing a free-body diagram, we draw a point to represent the body. Sometimes we draw a square around the point to represent the body.
The point (and possible square) should be drawn away from any other illustrations or diagrams.
On your free-body diagram, show each force on the object as an arrow. The direction of the arrow should be the same as the direction of the force. Whenever possible, the length of the arrow should be roughly proportional to the size of the force.
All arrows representing forces begin at the point.
Each force in the diagram should be clearly labeled.
1. What do you notice when you try putting different weights on the bottom of the spring?
2. What is the difference between using a "softer" vs. "harder" spring when you hang more weight on it?
3. Draw the free body diagram for three different weights you hang on the springs.
4. EXTRA CREDIT: explore how (1) friction (2) different locations, g, etc affects the motion of the spring. Write down your observation and analysis in a paragraph format. You may want to do research on these topics to help you understand what you are observing. Don't forget to cite all the sources.
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