## Pushy Kids in Physics

### Gencie WhiteSanta Rosa District Schools

#### Description

This is an interesting way to introduce balanced forces, unbalanced forces, and resulting net forces. Students actively demonstrate these concepts and then study and complete the activity with actual calculations of these forces.

#### Objectives

The student knows the effects of the four basic operations on whole numbers, fractions, mixed numbers, decimals, and integers.

The student recognizes the forces that act on a given object.

The student knows that forces may be balanced or unbalanced.

The student understands that unbalanced forces cause objects to accelerate.

The student knows ways in which a net force (for example, the sum of all acting forces) can act on an object (for example, speeding up an object traveling in the same direction as the net force, slowing down an object traveling in the direction opposite of the net force.

#### Materials

-Student volunteers (5 suggested)
-Related text material on balanced, unbalanced, and resulting net forces
-White board or overhead projector and markers
-Calculating Net Forces-Examples for each student (See Associated File)
-Calculating Net Forces worksheet for each student (See Associated File)
-Calculating Net Forces-Answer Key for teacher use (See Associated File)
-Pencils
-Calculators (optional)

#### Preparations

1. Include with a unit on force and motion.
2. Locate the appropriate related textbook material to complete lesson.
3. Make copies of the Calculating Net Forces-Examples and the Calculating Net Forces worksheet for each student. (See Associated File)
5. Gather the necessary materials.
6. Optional: An FCAT-gridded response key could be utilized along with this activity.

#### Procedures

1. Select several students to assist in a classroom demonstration. (5 suggested) Please note that the first five steps are the attention getter. The students will not have enough information to fully understand the concepts until the rest of the lesson has been taught.

2. Assign students their roles. Without any more information, 4 of these students represent forces (for simplification all 4 are representing an equal amount of force) and one represents the object being acted upon. In the accompanying worksheet the object acted upon is a box.

3. Be sure to remind students of appropriate behaviors and safety involved. Although we are talking about the push of forces, make sure students are reminded about a demonstration GENTLE push and that no type of inappropriate pushing, shoving, or rudeness will be tolerated. (Carefully select your volunteers!)

4. Have the students pretend to be their assigned forces acting on another object (yet another volunteer).

5. Set up your demonstration so as to show the class that a force acting on an object causes the object to accelerate in the direction of the net force. To simplify, start with:

a. One force pushing to the right.
b. Then one force pushing to the left.
c. Then two forces, both pushing to the right.
d. Then two forces, both pushing to the left.
e. Next, two forces pushing in opposite directions on the same object.
f. And other situations of opposite forces on the same object.
g. And finally, start to demonstrate numerous forces acting in opposite directions.

6. Conduct a class discussion about what has just been demonstrated. Relate the activity to forces, net forces, and resulting movements (acceleration) of the objects as a result of these net forces. Remember that each student represents an equal amount of force for this demonstration. Include questions such as: Does a force cause an object to move? (Be aware that this lesson does not include static forces.) Do equal opposing forces cause an object to move? If more than one force is acting in the same direction, do they simply add together for a total force in that direction? In the more involved problems with several forces acting on the object, do you need to do some initial calculations before you can begin to do your work? It would always be best to initially calculate a total amount of force for each direction, and then do the final calculations of net force. Mathematically, if more than one force is acting upon an object, can we consider the cancellation of equal forces as a simplification? This builds upon students' prior knowledge about forces and that several forces can act on an object all at the same time. Now students actually calculate and identify the resulting net forces. Please remember that this activity deals only with forces acting in a single direction or in opposite directions.

7. Have students read and discuss the appropriate textual information on forces, balanced forces, unbalanced forces and resulting net forces. This is according to your available textbooks and relevant information on hand.

8. Ask the students to compare the initial activity to the information on forces. Encourage the students to come to the conclusion that they were actually demonstrating net forces. Ask them if they think that they would be able to predict or estimate the resulting forces on objects once the various forces along with their directions have been given. Make sure that the students understand that at this point we are only talking about forces in one direction or forces that are acting in opposite directions.

9. Briefly discuss this with the students and clarify any misconceptions that may have arisen. Address all questions.

10. Demonstrate examples on the board of single and multiple forces on single objects. Show the students that all forces acting in ONE direction simply become an addition problem to obtain the total force acting in that direction. Likewise, the sum of the forces acting in the opposite direction is the total force acting in that direction. Once the total forces have been calculated for each direction, it becomes a subtraction problem. The difference between the two total forces gives the resulting net force. And the resulting net force is moving in the same direction as the larger of the two directional forces.

11. Hand out the Calculating Net Forces-Examples and the Calculating Net Forces worksheet. (See Associated File)

12. Ask the students to work on the examples first. Give them time to complete the work. Then ask them to get into groups of three to share their results. Ask the students to share answers and try to come to an agreement. This is a way to encourage peer instruction. Any students can change their answers at this point as long as they agree with the changes. Their peers may lead them to an understanding of work and clear up their misconceptions. Once all groups have completed this process, send students back to their assigned seats. At this point have individual students act as teachers, go up to the board, and demonstrate each of the problems. Assist, ask students to help, and correct any student mistakes as they present at the board. At this point all students are to be checking their own work (modify to your discretion).

13. After all examples have been worked and the answers discussed, instruct students to individually complete the Calculating Net Forces worksheet. (See Assessments)

#### Assessments

Use the completed Calculating Net Forces worksheet to formatively assess the student's comprehension. (An Answer Key for both the Examples page and the worksheet is included in the associated file.)