Wheels

Question 0

Wagon-less Wagon experiencing 3 forces?

Answer 0

1) It’s downward weight
2) Support force from surface
3) Horizontal frictional forces from surface (violates N’s1st law?)

Question 1

Friction?

Answer 1

Forces exerted by surfaces on each other.

• Adheres N’s 3rd Law (all forces)
• Acts parallel (along) surfaces

Question 2

Frictional Forces oppose____?

Answer 2

relative motion b/w two surfaces in contact

• exerted parallel to the surfaces

Question 3

Relative Motion

Answer 3

Motion against velocity’s directio

Question 4

Surfaces in contact produce friction that has the same____?

Answer 4

Velocity, objects move together vs sliding across each other

Question 5

Frictional Forces are____ external forces on objects

Answer 5

Opposite

Question 6

Hold can w/ 2 fingers, exerting any frictional forces on can? In what direction forces?

Answer 6

Yes, exerting upward frictional force on can (your relative motion opposed by cans’ downward weight)
& .•. support cans’ weight

Question 7

Surfaces at rest & in contact ____ into____ _____ & are .•. particularly _____ to the ____ of ______.

Answer 7

1. Each other

2. Resistant to the start of sliding

Question 8

Friction depends (3)

Answer 8

• type of surface
• pressure of surfaces against each other
• whether/not surfaces actively sliding across

Question 9

Frictional Forces dependant on?

Answer 9

Support forces,

a bigger support force b/w 2 surfaces = bigger frictional forces

Question 10

of contact points proportional____

Answer 10

of support forces

Question 11

Contact points responsible for?

Answer 11

Frictional forces

Question 12

Amontons 1st law of friction?

Answer 12

Frictional forces b/w 2 surfaces are proportional to support forces b/w them.

Question 13

Amontons 2nd Law Friction

Answer 13

Frictional Forces b/w 2 surfaces don’t depend their apparent contact area.
- Surface you see touching floor not really (all) surface touching floor.

Question 14

For any two surfaces,

coefficient of friction = ?

Answer 14

frictional force (forces available when try sliding them/ support force (b/w 2 surfaces)

• typically 0.5, 0.3 etc.

Question 15

Frictional forces b/w tire & surface allow you to (3)?

Answer 15

1) speed up
2) slow down
3) turn

• w/out frictional you’d be inertialo

Question 16

Want tires that (2)

Answer 16

1) grip road well (higher coefficient of friction)

2) wheels tightly pressed against road producing higher support force b/w road & tire.

Question 17

Static Friction

Answer 17

Surfaces touching & not sliding across each other.

- forces causing surfaces not move (experience 0 net force & 0 acceleration

Question 18

Sliding Friction

Answer 18

Objects coasting across each other.

Question 19

The harder press 2 surfaces together___ the higher/lower (?) ___ ____ _____ can obtain

Answer 19

Higher peak static friction it can obtain

Question 20

Static friction is ____ & there’s a ____ of static friction before moving.

Answer 20

Adjustable & there’s a limit of static friction before moving.

Question 21

When gives up/at its limit frictional force turns into?

Answer 21

Sliding Friction

Question 22

When sliding box across floor need higher/lower force to start moving vs force keep box coasting?

Answer 22

Need higher force when first move box vs lower force needed keep coasting

Question 23

Coulomb’s 3rd Law of Friction

Answer 23

Sliding frictional forces are independent of sliding speed.

• faster you push/pull doesn’t affect force applied

Question 24

Sliding friction always in direction that____ ____ _____ to _____

Answer 24

Direction that opposes relative motion to surfaces.

Question 25

Static friction or Sliding friction higher force & better grip?

Answer 25

Static friction.
- mountain peaks grip together & settle in to make higher friction
vs
- mountain peaks sliding across each other.

Question 26

Is sliding friction adjustable & what does it depend on?

Answer 26

It’s not adjustable & it depends on how hard surfaces press each other (obey coulombs 3rd law friction)

Question 27

Sliding Friction wastes

Answer 27

Energy.

Question 28

(For moving box) sliding friction converts box’s ____ energy into ____ energy.

Answer 28

Kinetic energy into thermal energy.

Question 29

When box slides to stop on motionless floor, who does work on other?

Answer 29

Floor does negative work on box (pushes box opposite direction its velocity) &
Box does 0 work on motionless floor even though pushing on it.