## Lesson 10: Forces of Friction

## Overview:

## Curriculum Expectations:

**Overall Expectations:**

**B2.**Investigate, in qualitative and quantitative terms, forces involved in uniform circular motion and

motion in a plane, and solve related problems.

**B3.**Demonstrate an understanding of the forces involved in uniform circular motion and motion in a plane.

**Specific Expectations:**

**B2.1**Use appropriate terminology related to dynamics, including, but not limited to: inertial and non-inertial frames of reference, components, centripetal, period, frequency, static friction, and kinetic friction.

**B2.3**Analyse, in qualitative and quantitative terms, the relationships between the force of gravity, normal force, applied force, force of friction, coefficient of static friction, and coefficient of kinetic friction, and solve related two-dimensional problems using free-body diagrams, vector components, and algebraic equations (e.g., calculate the acceleration of a block sliding along an inclined plane or the force acting on a vehicle navigating a curve).

**B2.5**Analyse, in qualitative and quantitative terms, the relationships between the motion of a system and the forces involved (e.g., a block and algebraic equations to solve related problems sliding on an inclined plane, acceleration of a pulley system), and use free-body diagrams and algebraic equations to solve related problems.

## Success Criteria:

- A sprinter accelerates by pushing against the ground. Use a FBD to help you explain why the force is not perpendicular to the ground, and why it should not have too great a component parallel to the ground.
- How is the normal force and the force of kinetic friction related? What if instead it is static friction?
- What does the coefficient of static friction depend on? Give an example of a material with a large coefficient of kinetic friction and one with a small value.
- What is the upper limit of the force of static friction? What will happen to the object when this upper limit is exceeded?

## Time Allocation: 1 hour

## Learning A

ctivities:**Read**pages 84 - 89 from Nelson 2.4

FrictionLearn about position, velocity and acceleration vectors. Move the ladybug by setting the position, velocity or acceleration, and see how the vectors change. Choose linear, circular or elliptical motion, and record and playback the motion to analyze the behavior. |

Ramp: Forces and MotionExplore forces and motion as you push household objects up and down a ramp. Lower and raise the ramp to see how the angle of inclination affects the parallel forces. Graphs show forces, energy and work. |

In the playlist below, video:

- Will cover Newton's Second Law of Physics: F=ma. Without Pulley.
- Will cover Newton's Second Law of Physics: F=ma. With Pulley.

**Practice**questions 2, 3, 4, and 8 on page 89.

## Task:

**Solve**questions 1, 2, and 6 from Nelson 2.4 Review on page 90.

Quiz Chapter 2 on Moodle.

*Optional Extension:*- Solve questions 4, 7, and 8 on page 90.

## Reflect:

In a sport such as curling, friction affects how far a moving stone will travel along the ice. Sweeping the ice in front of a moving stone reduces the force of friction acting on the stone. The result is that the stone slides farther.

Friction can be helpful in some situations but cause problems in other situations.

(a) Think about two situations in which friction is helpful for an object moving on a horizontal surface.

(b) Think about two situations in which it would be ideal if there were no friction when an object moves across a horizontal surface.

(a) Think about two situations in which friction is helpful for an object moving on a horizontal surface.

(b) Think about two situations in which it would be ideal if there were no friction when an object moves across a horizontal surface.