Forces at Rest

Misconception: If an object is at rest, no forces are acting on the object. (

Instruction Framework: T-GEM

Digital Technology: PhET

Lesson Sequence:

I. Warm up – Classroom

Use a toy car on a platform to do some demonstrations and ask students about forces that are acting on them:

  • push the toy car to the right constantly
  • push the toy car to the right and let go
  • push a toy car to the right then slow it down by pushing it in the opposite direction
  • let the toy car sit on the platform by itself

This warm up activity is designed to get students thinking about forces and to bring forward any misconceptions related to how forces make objects move, speed up, slow down, or be at rest.

II. Generate Hypotheses – Classroom

Show students examples where objects are at rest. Example 1 is of the toy car from activity I staying motionless on a platform.  Example 2 is a second toy car hanging from the ceiling with a string, once again at rest.  Ask students what kinds of forces might be involved in keeping the toy cars motionless.  Ask students to draw free body diagrams of the two examples, share with a partner, then ask for some volunteers to draw their free body diagrams on the board.

III. Evaluate Hypotheses – Computer Lab

Students are taken to the computer lab with their free body diagrams from the previous activity.  Students are directed to the Forces and Motions PhET simulation and are asked to replicate the toy car demonstrations they saw in activity I.  For a refresher the demonstrations are written on the board:

  • push the toy car to the right constantly.
  • push the toy car to the right and let go.
  • push a toy car to the right then slow it down by pushing it in the opposite direction
  • let the toy car sit on the platform by itself

Instead of the toy car, they are free to choose an object in the simulation.

Students are asked to make sure the “Force Vectors” box is checked so they can visualize the different forces acting on the object.

Students are asked to compare their own free body diagrams from activity II and those shown in the simulation.  Students are asked to write down in their own words the similarities and differences between their free body diagrams from activity I and activity II.

IV.  Modify Hypotheses – Computer Lab

Students are asked to summarize the forces that act on objects when the object is moving, and when the object is at rest based on activities I, II, and II.

V.  Apply – Classroom

Students are paired up and each pair is given a small bucket filled with sand.  One partner is asked to stand up and hold the buckets motionless using one hand.  The teacher asks the pairs to draw free body diagram of this situation that show all the forces acting on that small bucket helping it remain motionless.



Conceptual understanding in science topics that includes force and motion is difficult because of the number of different misconceptions students bring with them into the classroom. DEMİRCİ, N. (2003) states, “It is evident from the literature that students of different educational backgrounds and different ages have basic preconceptions or misconceptions about force and motion concepts” (p. 40-41).  Khan (2012) suggests that, “the use of GEM in science classrooms can produce significant students gains in inquiry skills and conceptual understanding..” (p. 59).  It is this conceptual understanding that is critical to tackle misconceptions among students.  Khan (2012) also states that, “…T-GEM enhances student understanding” (p. 62).  Enhancing GEM cycles with technology (noted as T-GEM) can helps improve conceptual understanding of science topics.


PhET simulations are an excellent example technology enhancement to the GEM cycle.

Wieman, Adams, and Perkins (2008) describe PhET simulations in great detail and speak very positively of this interactive program.  Wieman et al. (2008) enumerate common features found in PhET simulation that enhance learning as below:

  1. “familiar elements…to build real-world connections” (Wieman et al., p. 682)
  2. “visual representations to show the invisible (the motion of air molecules in a sound wave)” (Wieman et al., p. 682)
  3. “multiple representation to support deeper understanding” (Wieman et al., p. 682)
  4. “multiple directly manipulated variables” (Wieman et al., p. 682)
  5. “instruments for quantitative measurements and analysis (measuring tape, clock, and pressure meter)” (Wieman et al., p. 682)

These different features truly allow students to be immersed in the concept, try out different scenarios and test hypotheses instantly.  These features combined make PhET an excellent tool for inquiry.  Khan (2012) airs caution however that simulations cannot be used by themselves as stand alone learning tools as doing so, “…contributes to poor uptake in science classrooms and “clicking without thinking” amount students” (p. 59).  Hence it is vital to pair PhET simulations with sound teaching methodologies like the GEM cycle, anchored instruction, or the LfU model.


DEMİRCİ, N. (2003). Dealing with misconceptions about force and motion concepts in physics: A study of using web-based physics program. Hacettepe Üniversitesi Eğitim Fakültesi, (24), 40-47.

Khan, S. (2012). A Hidden GEM: A pedagogical approach to using technology to teach global warming. The Science Teacher, 79(8). This article was written about T-GEM with middle-schoolers.

Wieman, C. E., Adams, W. K., & Perkins, K. K. (2008). PHYSICS. PhET: Simulations that enhance learning. Science (New York, N.Y.), 322(5902), 682-683.



  1. Hi Vibhu,

    Great lesson and particularly relevant for me as I’m currently covering this material in my Physics 11 class. I find that students likely misunderstand the concept of Fn and I particularly liked that that simulation showed the normal force. I also appreciated the ability to include Ffr on the crate as it allowed students to view frictionless and frictional surfaces.

    Thanks for sharing as I’ll definitely use this simulation the next time around.

    1. Hi Darren,

      I’m glad you found the simulation helpful. There are other really hood simulations you can check out!


  2. Thank you Vibhu for this lesson on forces and for sharing the reference to a list of 114 conceptions students might have in physics. Despite learning the “correct conception” students might still hold both (as we saw in Heather and the Private Universe), so it is interesting to aim to both tackle the misconception and the construction of the accurate conception in our lesson planning. I also liked how you clearly titled the phase or the main goal of the activity (eg. generate hypotheses, evaluate hypotheses, modify hypotheses).

    How might you ask questions (without leading students) to construct the idea that a force is acting upwards in 1, !V, and V, if students do not initially come up with this idea through the activity?

    To read about the affordances of WISE (CF. Weiman) and your analysis of how these affordances are particularly important to the TELE you have designed (try out different scenarios and test hypotheses instantly) helps to depict the thoughtful integration of the technology.

    Thank you, Samia

    Also, for those interested, John Clement discusses a teaching strategy called the bridging analogy which may be of use here: Clement, J. (1993). Using bridging analogies and anchoring intuitions to deal with students’ preconceptions in physics. Journal of research in science teaching, 30(10), 1241-1257 and, Brown, David E., and John Clement. “Overcoming misconceptions via analogical reasoning: Abstract transfer versus explanatory model construction.” Instructional science 18, no. 4 (1989): 237-261.

    1. Hi Samia!

      Asking students questions to lead them to understanding concepts is definitely an art and a challenge. To accomplish this task, I would relate the idea of Fn to Newton’s third law of equal and opposite forces. That would require coming up with intuitive demonstrations to convince students of the existence of the third law first, then asking students how might the third law apply to Fg and Fn.

      Thanks for helping me think more on this topic,

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