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Solving exercise C1 on page 21 of Physics 8 Textbook
Problem statement:
Find examples of sliding friction in everyday life and technology.
Solution:
- When braking a car, the wheels stop turning. The tire surface slides on the road, causing sliding friction that quickly stops the car.
- Friction between the table fan shaft and its bearing
- Friction between the bowstring of instruments like violin and the strings.
Solving exercise C2 on page 21 of Physics 8 Textbook
Problem statement:
Find additional examples of rolling friction in everyday life and technology.
Solution:
- In engineering: Friction occurs in the ball bearings between the rotating shaft and its bearing.
- In daily life:
+ When moving heavy objects, cylindrical rods can be used as rollers. The friction between the roller and the sliding surface is rolling friction.
When rolling a barrel on the floor, the frictional force between the barrel and the floor is called rolling friction.
Solve problem C3 on page 21 of the Physics 8 textbook.
Problem Statement:
In the scenarios depicted in figure 6.1, which scenario exhibits kinetic friction, and which exhibits rolling friction?
Based on the two scenarios above, what observations can you make about the intensity of kinetic friction and rolling friction?
Solution:
In Figure 6.1a of the textbook, three people push a sled on the floor, resulting in kinetic friction between the floor and the sled.
In Figure 6.1b of the textbook, a person gently pushes a sled with wheel cushioning, resulting in rolling friction between the wheels and the floor.
The two scenarios illustrate that the magnitude of rolling friction is significantly smaller than that of kinetic friction.
Solution to problem C4 on page 22 of Physics 8 textbook.
Problem Statement:
In experiment Figure 6.2, despite the applied pulling force on the heavy object, why does the object remain stationary?
Solution:
In Figure 6.2 of the textbook, despite the applied pulling force on the heavy object, the object remains stationary because there is a frictional force between the tabletop and the object. This force acts on the object and balances the pulling force.
Solution to problem C5 on page 22 of the Physics 8 textbook.
Problem Statement:
Find examples of static friction in daily life and engineering applications.
Solution:
Examples of static friction:
- In the production lines of many factories, products (such as cement bags, sugar bags, components, etc.) move along with the conveyor belt due to static friction.
In daily life, static friction enables people to walk without slipping, keeping their feet from sliding when stepping on the pavement.
Solution to problem C6 on page 22 of Physics 8 textbook.
Problem Statement:
Enumerate the drawbacks of frictional force and measures to reduce frictional force in the scenarios depicted in figure 6.3.
Solution:
a. The frictional force between the disc and the chain causes wear and tear on both, so lubricating the chain reduces friction.
b. The frictional force on the axle wears down the axle and impedes the rotational motion of the wheel. To reduce friction, replace with a bearing axle, significantly reducing friction compared to without a bearing.
c. The frictional force impedes the movement of the box when pushed. To reduce friction, use wheels to replace sliding friction with rolling friction (by placing the box on a wheeled table).
Solution to problem C7 on page 23 of the Physics 8 textbook.
Problem Statement:
Observe the scenarios depicted in figure 6.4 and imagine what would happen if there were no frictional force. Find ways to increase frictional force in these cases.
Solution:
a. A smooth, glossy board cannot be used for writing with chalk.
- Measure: Increase the roughness of the board to increase the sliding friction between the chalk and the board.
b. Without friction between the teeth of the nut and screw, the nut will gradually loosen when subjected to vibration. It no longer serves to tightly clamp the surfaces being joined.
When striking a match, without friction, the match head sliding on the matchbox surface will not ignite.
- Measure: Increase the roughness of the matchbox surface to increase the friction between the match head and the matchbox.
c. When braking suddenly, without friction, the car cannot stop.
- Measure: Increase frictional force by increasing the depth of the grooves on the surface of the car tires.
Solution to problem C8 on page 23 of the Physics 8 textbook.
Problem Statement:
Explain the following phenomena and determine whether friction is beneficial or detrimental in these cases:
a) Walking on freshly mopped tile floors increases the risk of slipping.
b) When a car enters muddy terrain, the wheels sometimes spin without the car moving forward.
c) Shoes worn out soles need replacement.
d) Apply pine resin to the bowstring at the arrow handle (the crane dance).
Solution:
a) When walking on freshly polished marble floors, slipping is likely due to minimal friction between the floor and human feet. Friction in this phenomenon is beneficial.
b) When a car drives into muddy terrain, the friction force between the car tire and the road surface is too small, causing the car wheels to slip on the road surface. Friction in this case is beneficial.
c) Shoes with worn-out soles are a result of the friction between the road surface and the shoe sole causing sole erosion. Friction in this case is harmful.
d) Apply pine resin to the bowstring at the arrow handle (the crane dance) to increase the friction between the bowstring and the violin string, thus making the violin string louder. Friction in this case is beneficial.
Solution for Exercise C9 Page 23 Physics Textbook Grade 8
Problem Statement:
What is the function of bearings? Why is the invention of bearings significant for the advancement of science and technology?
Solution:
Bearings function to reduce friction by replacing sliding friction with rolling friction of ball bearings. By using bearings, the resistance on moving objects is decreased, making machinery operate smoothly, contributing to the advancement of fields such as fluid mechanics, mechanics, and machine manufacturing... Therefore, the invention of bearings is crucial for the development of science and technology.
Fluid Pressure - Equal Pressure Vessels is an important lesson in Chapter I Mechanics. Check out the hints for Exercise Solutions on pages 28, 29, 30, 31 Physics 8 to grasp the knowledge better.
In Chapter I Mechanics Physics 8, you learn about Pressure. Before attending class, solve exercises on pages 25, 26, 27 Physics 8 to improve your understanding of Physics 8.
