5 Displacement and Force in Two Dimensions - Poulin's Physics

5 Displacement and Force in Two Dimensions

2 Friction

4(B), 4(D), 4(E)

MAINIDEA

Write the Main Idea for this section.

REVIEW VOCABULARY

Recall and write the definition of the Review Vocabulary term.

force

force

NEW VOCABULARY

Use your book to answer the questions below.

kinetic friction

1. Compare and contrast kinetic friction and static friction.

static friction

coefficient of kinetic

friction

coefficient of static

2. The slope of a line on a kinetic friction force v. normal force graph

is called the

coefficient of

kinetic friction and relates the friction force to normal force.

3. In the equation for the maximum static force, ¦Ìs is the

between two surfaces.

Science Notebook ? Displacement and Force in Two Dimensions

78

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friction

2 Friction (continued)

Student Edition, pp. 130¨C132

Describe the influence of static and kinetic friction when you are pushing

a couch.

GET IT?

Identify the two factors that affect friction forces.

Copyright ? McGraw-Hill Education. Permission is granted to reproduce for classroom use.

Write the equation for the kinetic friction force in the box, and state the

equation in words on the lines below.

Write the equation for the static friction force in the box, and state the

equation in words on the lines below.

Science Notebook ? Displacement and Force in Two Dimensions

79

2 Friction (continued)

Student Edition, pp. 132¨C133

Describe how coefficients of friction are measured, and identify factors

that can affect those measurements.

Complete the table below using your textbook.

Typical Coefficients of Friction*

Surfaces

Coefficient of static

friction (¦Ìs)

Coefficient of kinetic

friction (¦Ìk)

Glass on glass

Oak on oak

Steel on steel

*All measurements are for dry surfaces unless otherwise stated.

Use this column for

scratch work and

sketches.

TRY IT !

Problem

BALANCED FRICTION FORCES You push a 35.5-kg wooden box across a

wooden floor at a constant speed of 1.5 m/s. The coefficient of kinetic

friction is 0.15. How large is the force that you exert on a box?

1. ANALYZE AND SKETCH THE PROBLEM

KNOWNS

m=

v=

a=

¦Ìk =

UNKNOWN

=?

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80

Copyright ? McGraw-Hill Education. Permission is granted to reproduce for classroom use.

Use with Example Problem 3.

2 Friction (continued)

Student Edition, p. 133

TRY IT ! (CONTINUED)

2. SOLVE FOR THE UNKNOWN

The normal force is in the y-direction, and the box does not accelerate in

that direction.

The pushing force is in the x-direction; v is constant, thus the box does

not accelerate.

3. EVALUATE THE ANSWER

? Does the answer make sense?

Copyright ? McGraw-Hill Education. Permission is granted to reproduce for classroom use.

SUMMARIZE

How does the MAINIDEA for this section relate to the chapter¡¯s BIGIDEA?

REVIEW IT !

27. MAINIDEA Compare static friction and kinetic friction. How are the frictional forces

similar, and how do the forces differ?

Science Notebook ? Displacement and Force in Two Dimensions

81

2 Friction (continued)

28. Friction At a wedding reception, you notice a boy who looks like his mass is about

25 kg running across the dance floor then sliding on his knees until he stops. If the

coefficient of kinetic friction between the boy¡¯s pants and the floor is 0.15, what is the

friction force acting on him as he slides?

29. Velocity Dinah is playing cards with her friends, and it is her turn to deal. A card has a

mass of 2.3 g, and it slides 0.35 m along the table before it stops. If the coefficient of

kinetic friction between the card and the table is 0.24, what was the initial speed of the

card as it left Dinah¡¯s hand?

30. Force The coefficient of static friction between a 40.0-kg picnic table and the ground

below that table is 0.43. How large is the greatest horizontal force that could be exerted

on the table without moving the table?

32. Critical Thinking Rachel is moving to a new apartment and puts a dresser in the back

of her pickup truck. When the truck accelerates forward, what force accelerates the

dresser? Under what circumstances could the dresser slide? In which direction?

Science Notebook ? Displacement and Force in Two Dimensions

82

Copyright ? McGraw-Hill Education. Permission is granted to reproduce for classroom use.

31. Acceleration You push a 13-kg table in the cafeteria with a horizontal force of 20 N,

but the table does not move. You then push the table with a horizontal force of 25 N,

and it accelerates at 0.26 m/s2. What, if anything, can you conclude about the

coefficients of static and kinetic friction?

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