Ricky Held

Kathleen McCabe

ESSC 311

Kovacs

MWF 10:00

Multiple Forces Acting on One Object

Goal: The goal of this lesson is that the students should develop knowledge about how multiple forces act on an object. They should also develop understanding of how the net force on an object is affect when multiple forces are in play and in differing or concurrent directions.

Objective: The objective of this lesson is for students to gain an understanding of what happens when two or more forces act on a given object in the same direction and in opposite directions. They should understand that when two or more forces act on an object in the same direction (to start and keep the object moving horizontally), each force will be smaller. They should also understand that when two or more forces act on an object in opposite directions (to start and keep the object moving horizontally), each force will be greater. The direction that the greater force is applied will be the direction that the object moves

Grade Level Content Expectation: P.FM.05.31-Describe what happens when two forces act on an object in the same or opposing directions.

Materials:

  • Thick or strong jump rope
  • Force spring scales
  • “Masses” (can be blocks of wood, plastic, etc. Students must be able to attach a spring scale to these)
  • Angled ramps (text books can be used for this purpose)

Introductory Set: The students will take place in a tug of war. Have students exit the room and enter the hallway or go outside. Choose 10 students* and have half of the group take one side of the rope and the other half take the other side of the rope. Now have the students tug on both ends, just like in a standard tug of war. Have them remember the outcome. Pick another 10 students*, this time put only 3 on one side of the rope and 7 on the other side. Have them perform the tug of war and remember the outcome.

Once back inside the classroom discuss the outcomes of the tug of war matches. Ask the students why they think the winners won. The answer is that the winners applied a greater force. Next point out that the two teams were applying force in opposite directions.

*The number of students is arbitrary. Choose a number of students based on the length of and perceived durability of the rope that you have for the tug of war.

Procedure: After the introductory set, explain the necessary material to the students using the Forces Power Point.

After the lecture portion of the lesson is complete, the students will take part in a hands on experiment. Before the lesson, divide the spring scales and blocks into packets to be passed out to groups. Each packet should contain 2 spring scales, one block, and one ramp, if the ramps being used aren’t the students’ text books. Instruct the students on how to proceed with the experiment using the step-by-step directions located on the experiment instruction sheet and also found in the power point lecture.

Assessment: After the experiment, the students will discuss their findings as a class. Their understanding of the content will be based on the connections they make with the experiment and the lecture. An example of an observation that reflects understanding would be “When there were two forces acting on an object in the same direction, each force was half as much as when there was only one force acting on an object. However, it still takes the same amount of force to move the object.”

Comparing Forces

In this experiment we will compare the relationship between different force combinations.

  • First we will measure the amount of force it takes to move an object when only 1 force is acting on it.
  • Next we will measure the amount of force it takes to move an object when two forces act on an object in the same direction.
  • Finally, we will measure the amount of force needed to move an object when two forces act on an object in opposite directions. Record your results in the table below.

PROCEDURE

One force acting on an object:

  1. Attach a spring scale to the object
  2. Pull on the spring scale at a constant speed
  3. Read and record the number in grams

Two forces acting on an object in the same direction:

  1. Attach two spring scales to the same side of the object
  2. Pull on the spring scales attached to the object at a constant speed
  3. Record each force on the different spring scales in grams

Two forces acting on an object in opposite directions:

  1. Attach one spring scale to the object
  2. Place the object on a steeply angled ramp. This angle will allow gravity to pull the object “downhill.” Gravity is the force acting on the object in a direction opposite to the pull of the spring scale.
  3. Pull the spring scale attached to the object at a constant speed and record the number in grams

RECORD YOUR DATA ON THE TABLE BELOW

1 Force (grams) / 2 Forces in same Direction (grams) (record both forces / 2 Forces in Opposite Directions (grams)
Object 1
Object 2
Object 3

CAN YOU SEE A PATTERN?