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http://weelookang.blogspot.com/2014/04/ejss-static-and-kinetic-friction-on.html

 

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This email address is being protected from spambots. You need JavaScript enabled to view it.; Francisco Esquembre

http://iwant2study.org/lookangejss/02_newtonianmechanics_3dynamics/ejss_model_frictionsec/frictionsec_Simulation.xhtml

Briefing Document: Frictional Model of Mass M = 1 kg Secondary JavaScript HTML5 Applet Simulation Model

1. Overview

This document provides a briefing on the "Frictional Model of Mass M = 1 kg Secondary JavaScript HTML5 Applet Simulation Model," a resource from Open Educational Resources / Open Source Physics @ Singapore. This is an interactive simulation designed to help students understand the concepts of friction and Newton's Laws of Motion through modeling. The simulation is built using Easy JavaScript Simulation (EJS) and can be embedded in web pages, accessible on various devices (including desktops, laptops, and mobile devices).

2. Key Themes and Concepts

• Newton's First Law (Law of Inertia): The resource introduces Newton's First Law through thought experiments. It states, "an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force."
• Example: The "coin on a playing card" example is used to illustrate how an object at rest tends to remain at rest if an external force (in this case friction) is not sufficient to move it when the playing card is pulled away quickly.
• Example: The "running friend stopping at a tape" thought experiment demonstrates that a moving object will resist a sudden change in motion.
• Forces and Free-Body Diagrams: The resource emphasizes the use of diagrams to represent forces. Arrows are used to indicate the magnitude and direction of forces, which is a crucial step in understanding the dynamics of motion.
• Quote: "Forces are usually indicated by arrows. The length of the arrow tells us how strong a force is: the longer the arrow, the larger the force."
• Friction (Static and Kinetic): The simulation focuses on demonstrating the differences between static and kinetic friction.
• Static Friction: The simulation shows how static friction opposes an applied force up to a certain limit, keeping an object at rest.
• Quote: "Even at Push = 4.905 N is balanced out by Friction Force and the block does not move."
• Kinetic Friction: The simulation models how kinetic friction acts when an object is sliding, and it's generally less than the maximum static friction.
• Quote: "after |v|>0, kinetic friction replaces as the frictional force."
• Net Force and Acceleration (Newton's Second Law): The resource highlights that acceleration occurs when there is a net force acting on an object (F=ma).
• Quote: "the condition of acceleration is the presence of non zero net force, which is F = ma, Newton's Second Law."
• Moments and Rotational Equilibrium: The simulation includes added calculations for moments and rotational effects, showcasing how the point of application of the normal force changes when a block is on an inclined plane, which effects whether the object will rotate or not.
• Quote: "normal contact force shifts to the extreme lower end of the block, just in position to not rotate clockwise."
• Quote: "normal contact force shifts beyond the extreme lower end of the block, in real life, block will rotate clockwise."
• Misconceptions: The resource explicitly addresses the common misconception that objects can move with a constant velocity while a pushing force is constantly applied.

3. Simulation Activities

The resource provides three core activities using the model builder, each representing a different scenario:

• Activity 1: No Net Force (Zero Push Force): When the net force is zero, the block remains stationary, with zero velocity. This represents the concept of inertia.
• Activity 2: No Net Force (Push <= Maximum Static Friction): When a pushing force is applied that is equal to or less than the maximum static friction, the block remains stationary, and the friction force balances out the push.
• Activity 3: Just Enough Push Force (Push > Maximum Static Friction): When a pushing force overcomes the static friction, the block starts sliding, and kinetic friction takes over. The acceleration of the object due to the net force is apparent.

4. Learning Outcomes

The learning outcomes of using the simulation are defined as:

• Understanding phenomena when no net force acts on a stationary or uniformly moving object.
• Predicting changes in motion based on the forces acting on an object.
• These are to be achieved "using modelling technique [diagrammatic models, mathematical models (dynamics equations), or any set of predictive and explanatory rules/principles]."

5. Additional Resources and References

The resource provides various links for further exploration:

• Blog Posts: Links to blog posts by the creator, detailing the design and development process of the model, and additional discussion of rotational effects.
• Other Simulations: Links to relevant simulations from PHET and other resources.
• Other OER: Links to a vast array of other open educational physics simulations.

6. Intended Use

This simulation is intended for secondary school physics education and can be used for:

• Interactive learning in classrooms or remote environments
• Supporting student investigations of the concepts related to dynamics and friction.
• Visualizing forces and their effects on motion, specifically in the context of static and kinetic friction.
• Enhancing understanding of the relationship between net force and acceleration, which is related to Newton's Second Law.

7. Summary

The "Frictional Model of Mass M = 1 kg Secondary JavaScript HTML5 Applet Simulation Model" is a comprehensive and accessible resource for teaching fundamental concepts in mechanics. Through interactive simulations and modeling activities, it facilitates a deep understanding of Newton's Laws of Motion, particularly focusing on the role of friction, net force, and acceleration. The inclusion of moments calculation expands the model's scope beyond basic translational motion, providing insight into when rotation will occur. The resources offered within the site (links to other simulations, blog posts, etc.) further enhance its educational value.

 

Frictional Model Study Guide

Quiz

Instructions: Answer the following questions in 2-3 sentences each.

1. According to Newton's First Law, what happens to an object if no external forces act upon it?
2. In the context of the simulation, describe what happens when the applied push force (Fapp) is less than the maximum static friction force.
3. What is the difference between static and kinetic friction?
4. Explain the significance of the arrows used in force diagrams, according to the provided text.
5. What is the relationship between the net force acting on an object and its acceleration, according to the "Big Idea" section?
6. Describe a real-world example of Newton's First Law in action, based on the "Engage for Newton's 1st Law" section.
7. What happens to the normal contact force on a block resting on a slope as the angle increases from zero to beyond 45 degrees?
8. Explain the concept of "no net force" in terms of an object's motion.
9. What is the purpose of using a simulation in this context, according to the learning outcomes?
10. What potential misconception about force and motion is addressed in the "Misconceptions" section of the text?

Quiz Answer Key

1. An object at rest will remain at rest, and an object in motion will continue in motion with the same velocity (both speed and direction), unless acted upon by an external force. This tendency of an object to resist changes in motion is known as inertia.
2. When the applied push force is less than the maximum static friction force, the object remains stationary. The frictional force exactly counteracts the applied push force resulting in a net force of zero.
3. Static friction is the force that prevents an object from moving when a force is applied; it is the friction between non-moving surfaces. Kinetic friction, on the other hand, is the force that resists the motion of a sliding object, typically with a magnitude less than static friction.
4. In force diagrams, arrows represent forces. The direction of the arrow indicates the direction of the force, and the length of the arrow corresponds to the magnitude (strength) of the force.
5. The provided text explains that the acceleration of an object is directly proportional to the net force acting upon it, and inversely proportional to its mass (F=ma). A non-zero net force causes acceleration, changing an object's velocity.
6. In the provided thought experiment, a person running and trying to stop abruptly on a line demonstrates that their forward motion is not immediately removed, due to inertia, requiring an opposing force to bring them to a stop.
7. As the angle increases, the normal contact force on a block shifts towards the lower end of the block, and at angles greater than 45 degrees, the normal force would be positioned in such a way that the block would rotate clockwise.
8. "No net force" implies that the sum of all forces acting on an object is zero. In this case, an object will either remain at rest or move at a constant velocity in a straight line; acceleration is zero.
9. The purpose of using the simulation is to provide a virtual environment where students can experiment with different force scenarios. They can observe the resulting changes in motion and better understand the relationship between force and motion.
10. Students may believe it’s possible for an object to move with constant velocity while a continuous force is applied. In reality, constant velocity occurs when there is zero net force, such as when the applied force is balanced by friction.

Essay Questions

Instructions: Answer the following questions in essay format (multiple paragraphs).

1. Using the concepts presented in the provided text, explain how the interplay between static friction, kinetic friction, and an applied force results in the acceleration of an object. Provide real-world examples to support your explanation.
2. Critically analyze the effectiveness of using simulations, like the one described in the text, as educational tools for teaching physics concepts such as Newton's Laws and frictional forces. Discuss the advantages and potential limitations.
3. How do the concepts of force diagrams and modeling relate to the "Learning Outcomes" listed in the text? Provide a detailed explanation of how force diagrams and simulations are used to achieve the given objectives.
4. Discuss how the "Misconceptions" section of the text highlights a common misunderstanding of physics concepts. Elaborate on why these misconceptions might arise and suggest ways to address them in an educational setting.
5. Analyze how the inclusion of "Added Moments Calculations" in the simulation expands the educational value. Discuss how this feature helps in understanding the conditions necessary for rotational motion in addition to linear motion.

Glossary of Key Terms

Net Force: The overall force acting on an object, which is the vector sum of all individual forces.

Static Friction: The force that prevents an object from starting to move when a force is applied.

Kinetic Friction: The force that opposes the motion of an object that is already sliding.

Force Diagram: A diagram that uses arrows to represent the direction and magnitude of forces acting on an object. Also called a Free Body Diagram.

Newton's First Law (Law of Inertia): An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.

Newton's Second Law: The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass (F=ma).

Maximum Static Friction: The largest amount of static friction that can be exerted before an object begins to move.

Normal Force: The force exerted by a surface on an object that is in contact with it, acting perpendicular to the surface.

Acceleration: The rate of change of an object's velocity.

Modeling: The process of creating representations (diagrams, equations, simulations) to understand and explain physical phenomena.

Learning Outcomes

1. To explain and understand phenomena when there is no net force acting on a stationary object, or on an object that is moving in a straight line using modelling technique [diagrammatic models, mathematical models (dynamics equations), or any set of predictive and explanatory rules/principles].
2. To predict changes in motion (if any) of an object based on the forces acting on it using modelling technique [diagrammatic models, mathematical models (dynamics equations), or any set of predictive and explanatory rules/principles].

Worksheet

1. Dynamics - student worksheet (gwf - dl - wlk).docx
2. Dynamics - student worksheet (gwf - dl).docx
3. Dynamics - student worksheet (lyna).docx

Video

 Frictional force modelling with simulation activity by lookang lawrence wee

Imagine you put a playing card on top of a cup, then a coin on top of the playing card. Quickly pull the playing card away. What will happen to the coin? Explain your answer. Watch the video at http://tinyurl.com/ast2016-1 and check your prediction

 Newtons 1st Law-coin and glass by Nick Alsleben

Engage for Newton's 1st Law

Imagine placing a strip of tape on the floor. Then you ask a friend to run towards you from about 30 meters as fast as possible and to stop exactly on the tape. What will happen to your friend when he or she tries to stop? Explain your answer

Suggested answer:

What you demonstrated in your two thought experiments, is Newton’s First Law. It states that

“an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.”

In case 1 (video above), the coin stayed in place, as the card was pulled away so fast, that friction did not act. In case 2 (engage for newton's 1st law), your friend had some forward motion, that could not be removed immediately.

Pre Modeling Activity

In this activity, you will be asked to draw forces in diagrams. Forces are usually indicated by arrows. The length of the arrow tells us how strong a force is: the longer the arrow, the larger the force.

In the example, we see two vertical forces acting on a Wooden Block resting on a slope. Its Fgrav= Weight is pulling it down and Fnorm = contact force on block by slope, an upward force. The Ffrict is the frictional force arising when there is a Fapp = Push to the right.  The fact that the arrows are equally large, tells us that the two forces have the same magnitude. 

Modeling Activity 

Modeling Activity using this #html5 simulation

No Net Force (no Push Force )Model

Tom has just been promoted and is pushing a file cabinet down the hall to his new office. He begins by looking at the file cabinet and considers how to best go about his task. Select Fx = 0 to model the zero force model. Note the motion of the block is no change in position and velocity is zero all the time.

Activity 1: Using the model builder, select Fnet_x = 0 to simulate this effect

No Net Force ( 0<|Push| => Maximum Static Friction) Model

He then begins pushing on the file cabinet, which, at first, does not move at all. To simulate this case, select Push to be 3 N and observe what happens to the motion of the block. Note that the Push is cancel out by the Friction Force. Even at Push = 4.905 N is balanced out by Friction Force and the block does not move.

Activity 2: Using the model builder, select Fnet_x = 0 to simulate this effect

Just Enough Push force (Push> Maximum Static Friction) to move Model

He pushes it slightly harder than the maximum static friction, and it is sliding . Thus, applying a Push force just larger than 4.905 N, the object begins to slide. But at t >0, the Friction becomes Kinetic Friction. 

Eventually the file cabinet begins to slide across the floor, slowly moving towards his new office with acceleration.   

Activity 3: Using the model builder, select Fnet_x = 3.038 to simulate this effect. note that the static force is just a force to overcome initial when v = 0, after |v|>0, kinetic friction replaces as the frictional force.

Big Idea

Thus, the evidences and model building process above suggests the condition of acceleration is the presence of non zero net force, which is F = ma, Newton's Second Law.

Misconceptions

Students may think that it is possible to experience is pushing the file cabinet, and it is moving to the right with constant velocity.

Added Moments Calculations

as suggested by workshop participant from JJC, moments are calculated and reflected in simulation!

angle = 0, block does not rotate https://sg.iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/02-dynamics/42-friction

angle = 45, block does not rotate, normal contact force shifts to the extreme lower end of the block, just in position to not rotate clockwise.https://sg.iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/02-dynamics/42-friction

 

angle > 45, block  rotates (but not simulated), normal contact force shifts beyond the extreme lower end of the block, in real life, block will rotate clockwise.https://sg.iwant2study.org/ospsg/index.php/interactive-resources/physics/02-newtonian-mechanics/02-dynamics/42-friction

 

Versions

1. http://weelookang.blogspot.sg/2016/02/frictional-block-free-body-diagram-with.html BlogPost by lookang with added moments calculations.
2. http://weelookang.blogspot.com/2014/04/ejss-static-and-kinetic-friction-on.html BlogPost by lookang
3. Sliding Down an Incline Plane Model by Francisco Esquembre http://www.compadre.org/osp/items/detail.cfm?ID=9973

Other Resources

1. http://phet.colorado.edu/en/simulation/legacy/forces-and-motion Forces and Motion by PHET
2. http://physics.bu.edu/~duffy/HTML5/static_friction.html Exploring static friction by Andrew Duffy

Frequently Asked Questions About Frictional Forces and Motion

• What is Newton's First Law of Motion and how does it relate to friction?
• Newton's First Law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. This law is directly related to friction, as friction is a force that can cause an object to slow down or stop. In the absence of a net force, including friction, a stationary object will remain stationary, and a moving object will continue to move at the same velocity in the same direction. However, in real-world scenarios, frictional forces often act to resist motion, altering an object's state. For instance, in the provided example, if a playing card is pulled away very quickly, a coin placed on top may stay in place due to inertia, as friction doesn't have enough time to act on it.
• How does static friction differ from kinetic friction?
• Static friction is the force that prevents an object from moving when a force is applied to it. The magnitude of static friction can increase to match the applied force up to a certain maximum value. Kinetic friction, on the other hand, is the force that opposes the motion of an object that is already sliding. Kinetic friction is generally less than the maximum static friction. This is why, in the example of a file cabinet, a greater push force is needed to start it moving than to keep it moving once it's sliding.
• What is meant by "no net force" and how does it affect an object's motion?
• "No net force" means that the sum of all forces acting on an object is zero. This can occur when there are no forces acting on the object at all or when the forces acting on the object are balanced, i.e., cancel each other out. According to Newton's First Law, an object experiencing no net force will either remain at rest or continue to move at a constant velocity in a straight line, meaning there is no change in the object's state of motion. The simulation model demonstrates this, when Fx = 0 the object remains stationary with no change in position and velocity.
• How does applying a push force affect an object's motion when friction is involved?
• Applying a push force can lead to different outcomes depending on the magnitude of the push force relative to the frictional force. Initially, if the push force is less than the maximum static frictional force, the object will not move. If the push force is equal to the maximum static friction, the object will be on the verge of moving. If the push force exceeds the maximum static friction, the object will start to move and the frictional force will transition into kinetic friction, usually at a lower magnitude than the initial static friction. Once moving the objects motion will change depending on the net force, if the push force is balanced by the kinetic friction it will be at constant velocity, if it's greater than the kinetic friction it will accelerate.
• What role do free-body diagrams play in analyzing forces?
• Free-body diagrams are a tool used to visually represent all the forces acting on an object. Forces are typically indicated by arrows, where the length of the arrow indicates the magnitude of the force and the direction of the arrow shows the direction of the force. Free-body diagrams are critical for visualizing how different forces interact and for calculating the net force acting on an object. The example in the provided text shows a wooden block on a slope with the forces of gravity, normal force, applied force and frictional force all drawn with arrows of appropriate direction and size.
• How does the simulation model help in understanding the concepts of friction and motion?
• The simulation model allows for the visualization and testing of various scenarios involving frictional forces. It models several conditions including no force, zero net force, applying push forces and exceeding static friction. By varying the applied push force and observing the resulting motion, learners can develop a more intuitive understanding of how static and kinetic friction influence an object's motion, and how those forces interact with an applied force. The model includes calculation of moments, which allows students to observe the impact of the application of forces at different angles on rotation of the object.
• What is the relationship between net force and acceleration according to Newton's Second Law?
• Newton's Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This is often expressed in the equation F=ma, where F represents the net force, m represents mass, and a represents acceleration. Thus, a non-zero net force is required for an object to accelerate and this relationship is shown in the simulation when Fnet_x is greater than zero and the object starts to move with acceleration.
• What are some common misconceptions about friction and motion?
• One common misconception is that an object will always move in the direction of the applied force and at a constant velocity if it is in motion. Students might think it is possible to push a file cabinet, and it will move at a constant velocity when there is a net push force. However, this misunderstands the role of friction and Newton's First and Second Laws, that the object is affected by an external force. In fact a push force balanced by a frictional force results in constant velocity, whereas a push force greater than the frictional force is needed for acceleration. Additionally, the concept of static friction is often misunderstood, with people thinking that objects always move if you push them even when the static frictional force is greater.