1. it is a common practice to put oil in a car and to change the car’s oil oin a while. why do cars need oil?
2. which two of the following statements are true?
a. sliding friction is typically greater than static friction.
b. static friction is typically greater than sliding friction.
c. sliding friction occurs at rest and static friction occurs in motion.
d. static friction occurs at rest and sliding friction occurs in motion.
3. if the force squeezing two surfaces together is decreased, the force of dsliding friction between the two surfaces will most likely:
a. increase
b. decrease
c. stay about the same
4. name three devices or inventions that are designed to decrease friction.
5. name three devices or inventions that are designed to increase friction.
6. true or false? a well - oiled machine has no friction. explain your answe
7. a box is sliding across the floor from left to right. which diagram correctly shows the force of friction acting on the box?
(a) arrow right to box (b) arrow right to box side (c) arrow down inside box (d) arrow left to box side
8. true or false? friction makes energy vanish. explain your answer.
9. true of false? electronic machines with no moving parts experience friction and get hot because electricity is moving through the wires.
10. water is useful for reducing friction between objects. however, you also learned that (due to friction) moving water causes rough rocks to become smooth. how can this be?

Question

1. it is a common practice to put oil in a car and to change the car’s oil oin a while. why do cars need oil?
2. which two of the following statements are true?
   a. sliding friction is typically greater than static friction.
   b. static friction is typically greater than sliding friction.
   c. sliding friction occurs at rest and static friction occurs in motion.
   d. static friction occurs at rest and sliding friction occurs in motion.
3. if the force squeezing two surfaces together is decreased, the force of dsliding friction between the two surfaces will most likely:
   a. increase
   b. decrease
   c. stay about the same
4. name three devices or inventions that are designed to decrease friction.
5. name three devices or inventions that are designed to increase friction.
6. true or false? a well - oiled machine has no friction. explain your answe
7. a box is sliding across the floor from left to right. which diagram correctly shows the force of friction acting on the box?
   (a) arrow right to box (b) arrow right to box side (c) arrow down inside box (d) arrow left to box side
8. true or false? friction makes energy vanish. explain your answer.
9. true of false? electronic machines with no moving parts experience friction and get hot because electricity is moving through the wires.
10. water is useful for reducing friction between objects. however, you also learned that (due to friction) moving water causes rough rocks to become smooth. how can this be?

Accepted Answer

### Question 2
# Brief Explanations:
To determine the true statements, we analyze friction types:
- Static friction acts on objects at rest (opposing initiation of motion), and sliding friction acts on moving objects (opposing sliding motion). So statement d is true.
- Static friction is typically greater than sliding friction (it takes more force to start moving an object than to keep it sliding). So statement b is true.
- Statement a is false (sliding friction is less than static friction), and statement c is false (mixes up when each friction acts).
# Answer:
b. Static friction is typically greater than sliding friction, d. Static friction occurs at rest and sliding friction occurs in motion

### Question 3
# Explanation:
## Step1: Recall the formula for sliding friction
The force of sliding friction $ F_f = \mu_k F_N $, where $ \mu_k $ is the coefficient of kinetic friction and $ F_N $ is the normal force (force squeezing surfaces together).
## Step2: Analyze the effect of decreasing $ F_N $
If $ F_N $ (the force squeezing surfaces) decreases, and $ \mu_k $ remains constant (same surfaces), then $ F_f=\mu_k F_N $ will decrease because $ F_N $ is a factor in the formula.
# Answer:
b. decrease

### Question 4
# Brief Explanations:
Devices to decrease friction use methods like reducing surface contact, using lubricants, or adding rolling elements. Examples include:
- Ball bearings (convert sliding to rolling friction)
- Lubricants (like oil or grease, reduce friction between surfaces)
- Teflon coatings (low - friction surface)
# Answer:
Ball bearings, Lubricants (e.g., oil), Teflon coatings (any three valid devices like these)

### Question 5
# Brief Explanations:
Devices to increase friction use methods like increasing surface roughness or normal force. Examples include:
- Sandpaper (rough surface for more friction)
- Rubber soles on shoes (increase friction for grip)
- Brake pads (create friction to stop vehicles)
# Answer:
Sandpaper, Rubber - soled shoes, Brake pads (any three valid devices like these)

### Question 6
# Brief Explanations:
Friction is always present between surfaces in contact, even with oil. Oil reduces friction (by creating a lubricating layer) but does not eliminate it completely. So the statement is false.
# Answer:
False. A well - oiled machine still has friction, but the oil reduces the friction between its moving parts.

### Question 7
# Brief Explanations:
Friction opposes the direction of motion. The box is sliding from left to right, so friction acts to the left. Diagram D shows a force to the left, which is opposite to the box's motion direction.
# Answer:
D

### Question 8
# Brief Explanations:
Energy cannot vanish (law of conservation of energy). Friction converts mechanical energy into thermal energy (heat), but the total energy remains constant. So the statement is false.
# Answer:
False. Friction does not make energy vanish. It converts mechanical energy into thermal energy (heat), and the total amount of energy in the system is conserved.

### Question 9
# Brief Explanations:
Electronic machines with no moving parts do not experience mechanical friction (friction between moving surfaces). The heat in wires is due to electrical resistance (Joule heating), not friction. So the statement is false.
# Answer:
False. Electronic machines with no moving parts do not experience mechanical friction. The heat in wires is caused by electrical resistance (Joule heating), not friction.

### Question 10
# Brief Explanations:
When water reduces friction between two objects, it acts as a lubricant. When moving water causes rocks to become smooth, the water carries abrasive particles (like sand) that act on the rocks, and the friction between the rocks and the abrasive particles (carried by water) causes the rocks to erode and become smooth. So in the first case, water is a lubricant; in the second, it transports particles that cause friction - based erosion.
# Answer:
When water reduces friction between objects, it acts as a lubricant. When moving water smooths rocks, the water carries abrasive particles (e.g., sand) that rub against the rocks. The friction between the rocks and these particles (aided by the moving water) causes the rocks to erode and become smooth.

Sovi.AI - AI Math Tutor

QUESTION IMAGE

Question

Explanation:

Question 2

Step1: Recall the formula for sliding friction

Step2: Analyze the effect of decreasing \( F_N \)

Answer:

Question 3