3. Friction Lab

Objective
Given lab equipment, students will be able to measure force required to pull baby shoes and identify factors that make pulling easier or harder.

Relationship to big idea
Everything physical in the universe is affected by forces.  These forces cause (or stop) motion.  In this lesson, students gain experience with friction and identify some factors that affect the size of the friction force.

Contribution to student understanding
The lesson helps students understand how real-life conditions on Earth, such as the presence of air resistance and other forms of friction, make it difficult to observe Newton's first law.

Essential question

How does the motion of a rock thrown in outer space differ from the motion of a rock thrown on Earth?  On other planets?

Set
Students complete a bell work assignment comparing situations where you might slip and fall versus situations where you can walk safely.  (Socks on a wood floor vs. shoes on dry cement, for example.)

Input
Remind students that a force is a push or a pull.  Today's lab will explore factors that affect how slippery baby shoes are (by measuring how hard you have to pull on baby shoes to make them slide).  They will answer the questions, "What things make baby shoes more slippery?  What things make them less slippery?"

Remind students of the definition of "variable" - something that can change each time an experiment is done.  In this experiment, students will examine the effects of several variables on the force needed to pull a baby shoe:

  • Shoe size
  • Type of surface (floor vs. carpet vs. cement outside)
  • Weight of shoe
  • Sole of shoe
  • Starting vs. continuing to pull

Tell students the unit used to measure force is called a Newton, abbreviated N.  The unit is named after Sir Isaac Newton, an important scientist we will learn more about later.

[After students complete the lab, explain "friction" as a force that stops or makes it harder for two things to slide past each other.  Distribute sandpaper - have students pull two pieces past each other.  Use rough surface of sandpaper as an analogy.]

Model

Demonstrate how to use force sensor to collect data.  Model collecting data and recording information on data sheet.

Check for understanding
Students summarize task in pairs.  Individual volunteers report task components to teacher; teacher lists tasks in order on board.

Guided practice
Students measure force for situations of their choosing and record data.

Students discuss results and group variables according to whether they make pulling easier or harder.

Closure
Teacher names variable (smooth sole on shoe, carpet, etc.).  Students confer with groups and check data, then chorally respond to indicate whether variable makes it harder or easier to pull a baby shoe.

Approaches and instructional strategies

Scaffolded inquiry: This is a level 2 (structured inquiry) activity.

Science for social justice: Many of my students are from large families and have young family members.  They can relate to choosing baby shoes that are unlikely to slip and therefore safe for a baby to wear.  The activity uses a familiar context to promote understanding of the abstract concept of friction.

Cooperative learning: Group members are assigned roles (materials manager, data recorder, tester, executive) which rotate with each test.  Groups work on demonstrating cooperative behaviors (take turns, use each other's names, encourage everyone to participate)

Productive questioning: As groups work, teacher asks students reasoning questions.  (What have you noticed about pulling shoes over carpet?  How many Newtons of force does it take to pull shoes on the floor?  How is adding more weight to the shoe like pulling it over carpet?  What would happen if we took weight out of the shoe?  Why do you think it's harder to pull the sneaker than the smooth-soled suede boot?)