Concept Presentation

Forces Acting on Objects

By:Sonu Bhutani

Specific Expectations• C2.1 use appropriate terminology related to

forces, including, but not limited to: mass, time, speed, velocity, acceleration, friction, gravity, normal force, and free-body diagrams

• C2.2 conduct an inquiry that applies Newton’s laws to analyze, in qualitative and quantitative terms, the forces acting on an object, and use free-body diagrams to determine the net force and the acceleration of the object.

• C2.5 plan and conduct an inquiry to analyze the effect of forces acting on objects in one dimension, using vector diagrams, free-body diagrams, and Newton’s laws.

• Forces and types of forces – Review

• Balanced and Unbalanced forces

• Free Body Diagram

• Calculation of net force

• Effect of forces

Lesson Sequence

What students should already know…

• Concept of force

• Types of forces

• Introduction to Newton’s Laws of Motion

Introduction to the topicThe concept of forces is fundamental for solving static and dynamic problems. The motion of a body will change only if an external force is applied to it. If several forces are acting on an object, vector sum of all forces that is the net force on the object might change an object’s state of motion. Free body diagram represent all the forces acting an object. The free body diagram allows you to set up problem properly so that you can correctly solve for unknowns such as forces and acceleration.

Balanced and Unbalanced forces-Video

http://www.teachertube.com/viewVideo.php?video_id=58727

Through this video teacher reviews concept of Balanced and Unbalanced forces.

Forces on a speeding fish

Upthrust

FrictionThrust

Weight

Demonstration: Introduction to Free Body Diagrams

Force diagramsForce diagrams help us understand forces.

The force is represented by an arrow.

The direction the arrow points shows the direction the force is acting.

The size of the arrow can be used to compare the size of the forces.

A force diagram for a falling object just after it starts to fall.

Air resistance

Weight

Free Body Diagrams-Video

This is an excellent video explaining how to draw free body diagrams with the help of different examples.

http://youtu.be/cErlwSUXwsg

Sample cards – Group activity

A block hangs at rest from the ceiling by a piece of rope. Consider the forces acting on the block and draw free body diagram.

A block slides across thetop of a table. Consider only the forces acting upon the block and draw free body diagram.

Drawing free body diagrams

Free Body Diagram - Animation

Through this animation, students can practice their skills at constructing free body diagrams.

www.physicsclassroom.com/shwave/fbd.cfm

Inquiry Based Learning: Computer Simulation

Through this simulation students will study qualitatively, how an external force will affect the speed and direction of an object’s motion with help of free body diagrams.

http://phet.colorado.edu/en/simulation/forces-and-motion

Potential difficulties by students

Students’ may face problem in:

• Drawing free body diagrams.

• Calculating net force.

• Explaining the effect of force with the help of free body diagrams.

Suggestions to student difficulties• To develop deeper understanding how to

draw free body diagrams, first visual aids are used and then group activity is assigned.

• To solve problems related calculation of net force, problem solving approach is used that helps in understanding the procedure well.

• Inquiry based learning is introduced that may help students in explaining affect of force using free body diagrams.

Assessment / EvaluationQuiz – Force and types of forces (K/U)Questioning during video – Balanced and Unbalanced forces (C)Demonstration Reflection – free body diagram (C)Group Activity Rating Scale – Drawing free body diagram (K/U & C)Lab simulation – Effect of forces (I/C)Culminating task rubric for lab simulation task sheet (I & C)Rubric for worksheet (K/U, A and C)Unit Test (K/U, A and C)

Accommodations for Special Needs and ELL

•Encouraging High achieving peers to assist the Special needs/ELL students in one to one settings.•Using hand on instruction, audio visual materials, games, pictures and flash cards.•Providing these students with extra time, computer options, assistive technology etc.•Providing more enrichment sheets to these students to practice.•Using co-operative learning setting, role play, field trips and games that may help to see natural/contextualized language.

Appropriate Internet sites related to topic

•http://www.physicsclassroom.com/Class/

The Physics Classroom Tutorial is an online physics tutorial with multimedia and shockwave studios.

•http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.htmlHyperPhysics is an exploration environment for concepts in physics which employs concept maps and other linking strategies to facilitate smooth navigation.

•http://phet.colorado.edu/This site contains interesting computer simulations helping students to develop deeper understanding about concept.

•http://www.mrfizix.com/home/applicationnewtonlaws.htm#_topYou can find answers to your most complex physics questions, and even find ideas for lab experiments and projects.

Practical applications & societal implications

Knowledge of force is required:In principles of launching satellites and rockets.In working of cranesIn designing of Golf clubsIn development of technologies such as crumple zone, seat belts and air bags.By mountain climbers as they use nylon ropes.By a driver as negotiating sharp turns.