Chapter 12 What You Will Learn Friction Magnitude (size) Section 3 Friction: A Force That Opposes Motion Chapter 12 What You Will Learn Friction Magnitude (size) Kinetic friction Static friction

Chapter 12 What You Will Learn Section 3 Friction: A Force That Opposes Motion Chapter 12 What You Will Learn 8.2.a Students know a force has both direction and magnitude. 8.2.c Students know when the forces on an object are balanced, the motion of the object does not change. 8.2.d Students know how to identify separately the two or more forces that are acting on a single static object, including gravity, elastic forces due to tension or compression in matter, and friction. 8.2.e  Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction).

Activity: Fingerprints Section 3 Friction: A Force That Opposes Motion Chapter 12 Activity: Fingerprints

Chapter 12 The Source of Friction Section 3 Friction: A Force That Opposes Motion Chapter 12 The Source of Friction When the hills and valleys of one surface stick to the hills and valleys of another surface, friction is created. Friction is a force that stops motion between two surfaces that are touching.

Chapter 12 The Source of Friction Section 3 Friction: A Force That Opposes Motion Chapter 12 The Source of Friction Friction is usually greater between materials that have rough surfaces than it is between materials that have smooth surfaces.

Activity: Friction Materials Section 3 Friction: A Force That Opposes Motion Chapter 12 Activity: Friction Materials

Chapter 12 Matter in Motion

Chapter 12 The Source of Friction Section 3 Friction: A Force That Opposes Motion Chapter 12 The Source of Friction As the force pushing surfaces together increases, the friction between the surfaces increases.

Activity: Feeling Friction Section 3 Friction: A Force That Opposes Motion Chapter 12 Activity: Feeling Friction

Chapter 12 Types of Friction There are two types of friction: Section 3 Friction: A Force That Opposes Motion Chapter 12 Types of Friction There are two types of friction: kinetic friction 2. static friction

Activity: Two Frictions Section 3 Friction: A Force That Opposes Motion Chapter 12 Activity: Two Frictions

Chapter 12 Types of Friction Section 3 Friction: A Force That Opposes Motion Chapter 12 Types of Friction 1. Kinetic friction is friction between moving surfaces. The force of sliding kinetic friction is greater than the force of rolling kinetic friction.

Activity: Rolling vs. Sliding Section 3 Friction: A Force That Opposes Motion Chapter 12 Activity: Rolling vs. Sliding

Chapter 12 Types of Friction Section 3 Friction: A Force That Opposes Motion Chapter 12 Types of Friction 2. Static friction can balance an applied force and can prevent changes in motion.

Chapter 12 Matter in Motion

Friction: Harmful and Helpful Section 3 Friction: A Force That Opposes Motion Chapter 12 Friction: Harmful and Helpful Harmful Friction (too little / too much) Helpful Friction (right amount)

DECREASE Harmful Friction Section 3 Friction: A Force That Opposes Motion Chapter 12 DECREASE Harmful Friction Lubricants ex: motor oil, wax, and grease decrease friction between the surfaces can decrease harmful friction Smooth the surfaces that rub against each other.

INCREASE Helpful Friction Section 3 Friction: A Force That Opposes Motion Chapter 12 INCREASE Helpful Friction Make the surfaces that rub against each other rougher. Increase the force pushing surfaces together.

Section 3 Friction: A Force That Opposes Motion Chapter 12 The End