Friction Teacher Guide





Physical Science

Grade Level

ES 3-4

Activity Name(s)


Penny Warming

Being Prepared

These experiments work better in small groups; suggested size of group is 2-3 students. Have a variety of shoes available for testing; students can bring in shoes from home to test. Shoes should be clean; beware of possible fungus or mold growing in shoes. Students may wish to wear gloves when handling shoes. Rubbing pennies causes the penny to heat up. Tell students not to place heated pennies on their skin.

Getting Started

Student will be using force sensors and quick response temperature sensors. Prior to starting the activities spend a few minutes explaining the use of both sensors. Students will need to know how to zero the force sensors. They need to know how to properly tape the temperature sensor to the paper so that the tape does not effect the ability of the sensor to take accurate readings. Showing students how to set up the senors using a projection unit would be helpful. They will need to know the proper way to run the simulation.

Suggested Timeline

Each activity will probably take two-45 min. class periods; depending on the speed of the students to type in their responses and the time to log onto computers. If they are proficient typists, they should be able to complete in one 45 min. class period per activity.

Thinking about the Discovery Questions

This unit is motivated by the discovery questions:

  • What affects the force of friction of shoes with the ground?
  • What affects how much a surface heats up when you rub it against another surface?

Friction is the force resisting motion between surfaces. In the standard model of friction there are some basic assumptions that are made. For example, frictional force is independent of the amount of surface contact or frictional force is proportional to normal force. While these are generally true there can be found exceptions to both ideas. Students have the misconception that friction is a force that you do not want. They see friction as hindering motion and feel it must be eliminated. They do not realize that they would not be able to walk across the floor if it were not for friction. Further there are times and situations where we want to reduce the amount of friction, for example an a skier wants to control the amount of friction depending on the snow conditions they are skiing in. Students believe some surfaces, such as ice, do not have any friction.

Learning Objectives

  • NGSS
    • Performance Expectations
      • 3-PS2-2. Make observations and/or measurements of an object's motion to provide evidence that that a pattern can be used to predict future motion.
      • 4-PS3-2. Make observations to provide evidence that energy can be transferred from place to place by sound, light, heat, and electric currents.
    • Disciplinary Core Ideas
      • ES-PS2: Motion and Stability: Forces and Interactions
        • PS2.A: Forces and Mation
          • The patterns of an object’s motion in various situations can be observed and measured; when that past motion exhibits a regular pattern, future motion can be predicted from it. (Boundary: Technical terms, such as magnitude, velocity, momentum, and vector quantity, are not introduced at this level, but the concept that some quantities need both size and direction to be described is developed.) (3-PS2-2)
      • ES-PS3: Energy
        • PS3.A: Definitions of Energy
          • Energy can be moved from place to place by moving objects or through sound, light, or electric currents. (4-PS3-2),(4-PS3-3)
        • PS3.B: Conservation of Energy and Energy Transfer
          • Energy is present whenever there are moving objects, sound, light, or heat. When objects collide, energy can be transferred from one object to another, thereby changing their motion. In such collisions, some energy is typically also transferred to the surrounding air; as a result, the air gets heated and sound is produced. (4-PS3-2),(4-PS3-3)
          • Light also transfers energy from place to place. (4-PS3-2)
    • Practices
      • Developing and using models
        • Develop and/or use a model to predict and/or describe phenomena.
        • Develop a model to describe unobservable mechanisms.
      • Planning and carrying out investigations
        • Collect data to produce data to serve as the basis for evidence to answer scientific questions or test design solutions under a range of conditions.
    • Cross Cutting Concepts
      • Patterns
        • Students recognize that macroscopic patterns are related to the nature of microscopic and atomic-level structure. They identify patterns in rates of change and other numerical relationships that provide information about natural and human designed systems. They use patterns to identify cause and effect relationships, and use graphs and charts to identify patterns in data.
      • Energy and matter: Flows, cycles, and conservation
        • Students learn matter is conserved because atoms are conserved in physical and chemical processes. They also learn within a natural or designed system, the transfer of energy drives the motion and/or cycling of matter. Energy may take different forms (e.g. energy in fields, thermal energy, energy of motion). The transfer of energy can be tracked as energy flows through a designed or natural system.
  • NSES
    • Physical Science - Light, heat, electricity, and magnetism
      • Heat can be produced in many ways, such as burning, rubbing, or mixing one substance with another. Heat can move from one object to another by conduction.
    • Physical science - Position and motion of objects
      • The position and motion of objects can be changed by pushing or pulling. The size of the change is related to the strength of the push or pull.

Discussion: Setting the Stage

  • What causes a ball rolling across the floor to slow down?

    Friction will cause ball to slow down.

  • What causes your ability to walk across the floor?

    As you walk across the floor, your feet push against the floor as the floor pushes against your feet. The two surfaces move against each other causing friction.

  • What is force?

    A push or a pull on an object caused by an interaction with another object.

  • What happens when you rub your hands together when you are cold?

    Your hands warm. The fast and harder you rub the warmer they will get.

  • What is conduction?

    The transfer of heat energy from one substance to another by touch.

Discussion: Formative Questions


  • Why is it important to have the shoe/water combination close to the same weight?

    Answers may vary but should discuss ideas relating to the amount of force needed to start movement might change if the weights are different. Also the idea that this will create a fair test.

  • Is the relationship between mass and force?

    The more mass, the more force will be needed to move the object.

  • What affects the amount of friction measured while pulling the shoes?

    The type of surface and the amount of mass pressing the two surfaces together.

Penny Warming

  • Would it make a difference if you were to rub at the same speed over a longer area? Explain.

    Answer will vary, though students may think that the longer the movement that more heat will be produced.

  • How does the amount of pressure you placing on the penny affect the heat measured?

    The harder you push down on the penny the more force required to start the movement. This should increase the amount of heat produced.

Discussion: Wrapping Up

  • Why do smaller cars slide easier on wet roads?

    Smaller cars have less mass which in general would increase the the likelihood of their sliding. You can control some of the slide by changing the amount of surface area where the tire meets the road.

  • How is rubbing your hands together like rubbing the penny on the table?

    In both rubbing creates friction; the faster you rub the more friction, the more heat.

  • Why are mountain bike tires different from regular bike tires?

    Off road riding is on uneven surfaces, rough surfaces, which require more friction.

  • Based on your results in the penny warming activity, if you wanted to make the maximum amount of heat with sticks to make a fire would you want to spin the sticks slow or fast?

    Answers may vary but should discuss that there appears to be greater heat produced when rubbing the penny quickly.

Additional Background

Friction is the result of two objects moving in relationship to each other. If is important to understand that this interaction takes place at the atomic or molecular level. The model in "Penny Warming" does a great job of explaining why. The types of surfaces that are interacting with each other affects friction. In general, the rougher the surface the more friction. Objects need to over come static friction in order to move; this requires additional force. When graphing friction with a force sensor, you will not get a straight line.



  1. What shoe bottom has the most friction? The least friction?

    This will depend on the type of shoes tested. In general, the rougher the surface, the more friction it will have.

  2. Why do they have different values?

    different shoes have different purposes. Mountain boots have more friction to help from slipping. Ballet shoes have less friction so you will be able to move easier across the floor.

  3. Which do you prefer for walking, dancing, running? Why?

    Walking shoes generally have less friction than running shoes and more than ballet shoes. When running, you use more force pushing against the surface. More force will require more friction so you gain traction and will be able to move without slipping.

Penny Warming

  1. Heat is a form of energy; it takes energy to heat up the penny. Where did the energy come from?

    The energy came from your use of your muscles. Your muscles got their energy from the food you ate which got its energy from eventually the sun.

  2. Why did the amount of heat differ from rubbing fast and slow?

    The more energy you put into something the more energy you get out. You applied more energy so there was more energy available to change into heat energy.

  3. Why did different surfaces matter?

    Different surfaces have different amounts of friction when rubbed together.

  4. Car breaks heat a lot when pressed. If you pressed harder, what would the effect be?

    The more you press, the more you are pushing the surfaces together. The harder you push, the more friction and therefore more heat.

Further Investigation

Displaying and discussing the Friction Plaground Slide model ( - from the ITSI model library) is a good application model to use to extend the activity. In addition, students can explore adding weights in equal increments to blocks of wood pulled by the force sensor to see if they can find a mathematical relationship between increasing mass and friction. Different coins can be used in the activity Penny Warming. The coins will have different surface images as well as be made up of different metals. Students might want to explore what different sports do to either increase or decrease friction to help them accomplish the goals of that sport (i.e. different tires in NASCAR, blades of ice skates, runners on sleds).