Lesson Objectives

  • Define force
  • Predict how different forces and combinations of forces will affect objects
  • Explain why a certain force had a particular effect on a certain object


Engage: Activate Prior Knowledge; Generate Interest

Display an image of a roller coaster.

Ask students to describe how they think roller coasters begin moving up a hill. What causes them to move up the track? What causes them to move down a hill once they are at the top? Keep a list of students’ ideas on the board or a piece of chart paper. (For example, students might suggest that the roller coaster has an engine that moves it forward, or that it is pulled by a chain to the top of a hill, or that gravity causes it to fall to the bottom of the hill.) Try to get most of your students to volunteer an idea. Then, point to each idea and ask, “Does this involve a force?” Have the class vote on each idea, and challenge students to explain why they voted yes or no.

Ask students, “What is a force?” Have each student work to define force by participating in a Think-Pair-Share with another student. Have pairs share their ideas with the class and use these ideas to come up with a class definition of force, which you should write on the board and which students should copy in their notebooks.

Explore: Allowing Students to Experience Content

Display the following questions to the students:
  • What is a force?
  • What effect does a force have on an object?
  • What happens when two unequal forces push an object in the same direction?
  • What happens when two unequal forces push an object in opposite directions?

Provide students with the reading passages May the Force Be with You and Chicken Collision; use the guiding questions as an advance organizer, discussing what information students will need to gather from the passages to help organize their note-taking.
You might want to assign the associated eBook passages, May the Force Be with You and Chicken Collision, to students instead of (or as a supplement to) the indicated reading passages. .
Have students identify information from the readings that will help to answer the essential questions. After students have read, allow them time to share what they have read with a partner. Post the essential questions on chart paper and have each group add information from their reading that will help answer the essential questions.

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Have students complete the Exploration About Force. The student worksheet will allow students to record their understanding as they progress through the activity. Once students have completed the Exploration, have them meet in small groups to discuss their results. For each combination of engines that students recorded on their worksheets, students should decide whether forces are added or subtracted and whether the result is a balanced or an unbalanced force.


Explain: Firm Up Understanding; Allow Students to Explain What They Know

Show the video segment The Physics of Skydiving to review the guiding questions for this session, focusing on how forces pushing in opposite directions allow a skydiver to fall safely to Earth.
Display the interactive glossary term, force. Have students record the definition in their notebooks, put the definition into their own words, and write a sentence containing the word.


Elaborate: Allow Students to Apply What They Know

Have students complete Level 1 of the virtual lab Pulling Your Weight.
Students should complete the student guide before and during the lab.


Have students analyze the data from the Virtual Lab. When was the force required to move the object the greatest? Why might this be the case? Have students relate the results of the investigation to real-world examples. Ask students if they have ever noticed that it is more difficult to push objects on carpets than it is to move objects on smooth tiled floors. Why is this the case? (Friction from the floor makes it harder to push an object. Rough surfaces have more friction than smooth surfaces.) Have students noticed that it is easier to push light objects and harder to push heavy objects? Have students draw conclusions about the relationship between applied force, mass, and friction.

Project Ideas: To help your students apply their understanding of force, you may wish to have your students complete some or all of the following projects. These projects can be completed outside of the classroom.

  • Students could identify forces used to perform work in their everyday lives and determine whether these forces are balanced or unbalanced. For example, to ride a bicycle requires that students push the pedals with their feet and the handlebars with their hands; when students are accelerating or decelerating, the forces are unbalanced.
  • Students could design a new toy that moves when various forces are applied to it. Students could simply sketch the design and label the applied forces, or students could attempt to construct the toy using everyday materials.
  • Students could design a parachute that will allow an egg to be dropped from a height without breaking, and then explain how balanced and unbalanced forces affect the falling egg. (The parachute creates a larger force from air resistance, and this force opposes the downward force of gravity; this slows the egg as it falls.)

Evaluate: Check for Understanding

Have students complete the Brief Constructed Response (BCR) item titled Force. You may also wish to assign the online concept assessment and use the results in the student reports to guide you in assigning any remediation to students