 Learning Objectives:  Explain the effects of friction on moving objects  Calculate the coefficient of sliding friction  Explain factors that may change the amount of friction  Success Criteria  Apply the definition of the coefficient of sliding friction, µ  Measure the coefficient of sliding friction between the soles of athletic shoes and a variety of surfaces  Calculate the effects of frictional forces on the motion of objects  Do Now:  Write learning objectives and success criteria (left side)  WDYS/WDYT (right side) ▪ Pg. 210  Agenda:  Do Now  LO/SC  Design Experiment

 Choose a group member’s shoe. This person will need to wear this shoe tomorrow and Wednesday too!

 READ ALL OF PG !!!  Design an experiment using the scientific method  Ask a question  Hypothesis/Prediction  Perform Experiment  Collect Data  Analyze Data  Draw Conclusion  Experimental Design Diagram Experimental Design Diagram

 How does changing the surface affect the amount of Force needed to pull a shoe?  By the end of the period you must have:  A hypothesis (If…then…because…)  Step by step procedures  Data table  All OK’d by Ms. Law

 Collect DATA!!!  Use your procedures from yesterday to collect data

 µ=force of friction perpendicular force exerted by the surface on object  µ=F f F N

 Complete #4 and record all data in your notebook  Be sure to answer ALL questions!

 Complete #5 and record all data in your notebook  Be sure to answer ALL questions!

 Do Now:  Draw a free-body diagram to show the relationships among the four force acting on the shoe moving at a constant speed. ▪ F pull ▪ F floor ▪ F gravity ▪ F friction  Agenda:  Do Now  LO/SC  Physics Talk  Quiz  Learning Objectives:  Explain the effects of friction on moving objects  Calculate the coefficient of sliding friction  Explain factors that may change the amount of friction  Success Criteria  Apply the definition of the coefficient of sliding friction, µ  Measure the coefficient of sliding friction between the soles of athletic shoes and a variety of surfaces  Calculate the effects of frictional forces on the motion of objects

 Newton’s 2 nd Law: motion with a constant velocity happens only when there is no net force or forces are balanced.  What does Newton’s 2 nd law say?

 What was the acceleration of the shoe when you pulled it in your experiment?  What does Newton’s 2 nd law imply about the force put on the pulled shoe?  The shoe was pulled with constant velocity=no acceleration  All of the forces must add up to zero/balance each other out.

 One of the forces was your pull on the shoe. How did you measure this force?  What force was pulling the shoe opposite of your pull to balance out the forces?  The force the shoe was pulled with was measured with a spring scale in Newtons.  Friction provided the second force. Friction is a force that resists relative motion between two bodies in contact.

 If you pulled at a constant speed, then was your pull (force) equal to the frictional force?  YES! Constant speed means balanced forces, no acceleration!

 What is net force?  Two forces that are equal in magnitude but opposite in direction are net forces  When you add up all the forces, you get the net force  Because they are acting on the same object! Both you pulling and friction were both acting on the shoe!

 What were the horizontal forces acting on the shoe?  Force of the pull  Force of Friction

 What were the vertical forces acting on the shoe?  What is another name for the force of the floor pushing up?  Gravity (down)  Floor (up)  This is also called the normal force! F N  Normal Force is perpendicular to the surface

 Draw and label all the forces acting on the shoe

 How do you calculate coefficient of sliding friction (µ)? µ=Force of friction Normal force µ=F f F N  The force of friction is equal to the force required to slide the object on the surface with a constant speed  No units  Usually a decimal

 Answer the WDYTN question on page 216