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Unit: Intro to Forces

Page history last edited by Shu-Yee Chen 10 years, 2 months ago

Unit: Intro to Forces

(Newton's 1st Law and 3rd Law of Motion)

 

 

 

Physics of Olympic Sport:

 

Central Concept-Newton's Laws of Motion: Newton's laws of motion and gravitation describe and predict the motion of most objects.

 

(more interesting discussion here: http://mythbustersresults.com/mythssion-control)

 

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.
12. Draw and interpret quantitative force diagrams.


 Vocabulary:

force

Free Body Diagram

(Force Diagram)

spring force
weight normal force
friction
tension Newton(s) net force
drag (air resistance)
gravity (gravitational force)
vector
spring constant
at rest balanced
unbalanced equilibrium
kinetic friction
static friction
interaction
inertia force constant motion velocity mass
weight kg N net force action force
reaction force balanced unbalanced equilibrium net force

 

 


Worksheets/Labs/Handouts:

 

Newton's 1st Law:

 

Newton's 3rd Law:

 

Past Year Handouts

 

Newton's 1st Law

 

Extra Worksheets from past years/review/challenge materials:

 


Supplement Material/Websites:

 

 

 Rules for Drawing Free-Body Diagram: 

 

 

(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.

 

End of the Unit:

Go to the following website and run the simulations for "Masses and Springs" http://phet.colorado.edu/en/simulation/mass-spring-lab (or, google "PHET simulations, masses and springs") Answer the following questions:

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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