 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

 How does changing the surface affect the amount of Force needed to pull a shoe?  Do #3 in your book, using spring scales and shoes from your table.

 Collect DATA!!!  Use procedure from book to collect data into a table form  Draw Conclusions:  Restate the question  Answer the question using data from experiment  Confirm or refute hypothesis and explain why

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

 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) (Normal Force)  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

 Do Now:  If I change the weight of an object, but keep the surfaces the same does µ change?  If I change the surfaces, but keep the weight the same, does µ change?  Agenda:  Do Now  LO/SC  Physics Talk  Reflection on LO and SC  HW  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

 Answer the WDYTN question on page 216  We need different shoes for different sports because there needs to be a specific amount of friction between your shoes and the surface. Friction is the force pulling in the opposite direction of motion. The force of friction and the force of the pull are opposite forces. The normal force and the force of gravity are opposite as well. µ is the Ff/Fn, and that tells us how much friction there is between 2 surfaces. If you have too much friction you will get stuck, if you have too little friction, you will slip and fall.

 Do Now:  Find each LO and SC in your notebook. ▪ Write pg # ▪ Write summary on left side page  Agenda:  Do Now  LO/SC  Discuss HW  Quiz  Ch Review  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