pulley
A simple machine that can rotate around the central axis consists of a grooved disc that can rotate around the central axis and a flexible cable (rope, adhesive tape, steel cable, chain, etc.). ) across the disk. Pulley is the deformation of lever, which belongs to lever simple machinery. In China, as early as the Warring States Period, there was a record about pulleys in the book Mo Jing. The pulley with the fixed central shaft is called the crown block, which is a deformed equal arm lever, and can change the direction of force without any effort. The pulley whose central axis moves with the weight is called the movable pulley, which is a deformed unequal arm lever, and can save half the force without changing the direction of the force. In practice, a certain number of moving pulleys and crown block are often combined into various pulley blocks. The pulley block can save labor and change the direction of force.
The differential pulley (commonly known as chain block) commonly used in factories is also a kind of pulley block. Pulley blocks are widely used in cranes, winches, elevators and other machinery.
There are two kinds of pulleys: crown block and moving pulley.
(1) The crown block is essentially an equal arm lever, which is labor-saving and effortless, but it can change the direction of the acting force.
Characteristics of crown block
It is not labor-saving to pull the hook code through the crown block. Whether there is a crown block or not, the reading of the spring scale is the same. It can be seen that the direction of force can be changed easily by using the crown block. Many times, changing the direction of force will bring convenience to work.
Crown block principle
The crown block is essentially an equal arm lever, and the power L 1 and the resistance L2 arm are equal to the pulley radius. According to the lever balance condition, it can also be concluded that the crown block is not labor-saving.
(2) The moving pulley is essentially a lever with twice the power arm as the resistance arm, which saves the force of 1/2 and spends the distance of 1 times more.
Characteristics of moving pulley
Using a moving pulley can save half the force and waste the distance. This is because when using the moving pulley, the hook code is hung by two ropes, and each rope only bears half the weight of the hook code. Although the use of moving pulley saves power, the distance of power moving is greater than the distance of hook code rising, that is, the distance is wasted.
Moving pulley principle
The moving pulley is essentially a lever, and its arm of force (L 1) is twice as big as the arm of resistance (L2).
(3) Pulley block: A pulley block consisting of a crown block following pulleys, which can save labor and change the direction of force.
The pulley block uses several lengths of rope to lift the object, and the force used to lift the object is a fraction of the total weight. The free end of the rope bypasses the moving pulley, but not the crown block.
The pulley block is labor-saving, but it consumes distance, and the distance of power movement is greater than that of heavy objects.
Purpose of pulley block:
In order to save energy and change the direction of power, the crown block and the moving pulley can be combined into a pulley block.
Labor-saving size
When using the pulley block, the pulley block uses several pieces of rope to lift the object, and the force used to lift the object is a fraction of the weight of the object.
Characteristics of pulley block
It is easy to see that the pulley block is labor-saving, but it consumes distance-the distance of power moving is greater than the distance of goods rising.
A simple machine that can rotate around the central axis consists of a grooved disc that can rotate around the central axis and a flexible cable (rope, adhesive tape, steel cable, chain, etc.). ) across the disk. Pulley is the deformation of lever, which belongs to lever simple machinery. In China, as early as the Warring States Period, there was a record about pulleys in the book Mo Jing. The pulley with the fixed central shaft is called the crown block, which is a deformed equal arm lever, and can change the direction of force without any effort. The pulley whose central axis moves with the weight is called the movable pulley, which is a deformed unequal arm lever, and can save half the force without changing the direction of the force. In practice, a certain number of moving pulleys and crown block are often combined into various pulley blocks. The pulley block can save labor and change the direction of force.
The differential pulley (commonly known as chain block) commonly used in factories is also a kind of pulley block. Pulley blocks are widely used in cranes, winches, elevators and other machinery.
There are two kinds of pulleys: crown block and moving pulley.
(1) The crown block is essentially an equal arm lever, which is labor-saving and effortless, but it can change the direction of the acting force.
Characteristics of crown block
It is not labor-saving to pull the hook code through the crown block. Whether there is a crown block or not, the reading of the spring scale is the same. It can be seen that the direction of force can be changed easily by using the crown block. Many times, changing the direction of force will bring convenience to work.
Crown block principle
The crown block is essentially an equal arm lever, and the power L 1 and the resistance L2 arm are equal to the pulley radius. According to the lever balance condition, it can also be concluded that the crown block is not labor-saving.
(2) The essence of the moving pulley is that the power arm is the resistance. ......
What are the benefits of roller skating?
1. Adjusting the amount of exercise can get various exercise effects, such as losing weight and so on.
-Burning 570 to 1 150 calories per hour is as good as running.
Generally speaking, the maximum oxygen consumption of roller skating (the benchmark for measuring exercise intensity) is 90% of that of running, which is very effective for maintaining the optimal intensity of aerobic exercise.
According to research, the heartbeat measured when skating at a speed of 23km/h is 74% of the maximum heartbeat. It is a typical aerobic exercise, which can strengthen the cardiovascular system and burn fat.
-When the speed is increased to 28km/hr, the heart rate will reach 85% of the highest heart rate and exceed the anaerobic threshold, which can improve muscle endurance.
You can adjust your body to the best condition by skating constantly.
2. The risk of injury is very small.
-Because roller skating is different from running, it will cause the wheels to turn when stepping, and the elasticity of the wheels made of polyurethane has little influence on the joints, so the elderly are also suitable for this sport. -Wear a helmet and protective gear, and there is little risk of injury after falling.
This is a very good exercise for growing children.
-Improve the sense of balance, exercise, physical strength and endurance, and help children grow and develop during their growth.
-Do more outdoor sports with others to make yourself cheerful.
-The effect of burning fat can prevent the symptoms of childhood obesity.
4. Exercise with your family
-From growing children to the elderly, men, women and children can enjoy sports together.
-Easy to learn exercise
Women are easy to learn. In fact, the ratio of male and female skaters is 50: 50.
5. Economic sports
-If you buy good equipment when you are a beginner, you hardly need to spend any other money.
-Unlike swimming, tennis and other sports, roller skating doesn't need a specific place, and it doesn't cost money like tickets.
-you can use it as a means of transportation according to your own strength.
You can make more friends by roller skating.
-Get to know more people and make many friends by participating in clubs and other activities.
-You can skate alone, and more people are interested in skating together.
7. It's not easy to get bored
-Roller skating can do leisure, speed skating, street brushing, flat flower, roller skating, pattern and other diversified sports, and will not get tired easily.
Look at the development of your roller skating skills, and you will have a great sense of accomplishment.
When you reach a certain technical level, you will get extra points in the college entrance examination.
-candidates who won the title of national second-class athlete or above in the same year and were tested and approved by the provincial admissions Committee. On the basis of the total score of candidates' unified examination results, the score can be appropriately improved.
What are the benefits of roller skates to the body?
First, enhance the coordination and balance of the body.
Roller skating is very beneficial to the balance, flexibility, adaptability and thinking ability of the body. The balance and coordination function of the body is mainly restricted by the flexibility, excitability and inhibition of the conversion ability of the nervous system. The human nervous system is one of the earliest and fastest developing systems, so children can exercise the function of the central nervous system as early as possible in the sensitive period of nervous system development, so that the body movements are coordinated, flexible, soft and powerful, which will benefit you for life. Roller skating also has the function of burning fat, which will prevent the symptoms of childhood obesity.
Second, exercise the ability and flexibility of joint support.
When playing roller skating, the knee joint and ankle joint need to support the body properly, and complete the actions such as supporting, sliding and turning, which has a good exercise effect on the supporting ability of the joint, especially the flexibility. The investigation on the problem of falls in the elderly shows that the supporting ability and flexibility of ankle joint are the key factors to prevent falls. Therefore, both children, teenagers and adults can benefit from roller skating.
Third, aerobic exercise can improve the whole body and mind.
Correct roller skating can actually improve your whole body and mind, because roller skating itself is a kind of aerobic exercise for the whole body. An athlete who has mastered the basic skills of roller skating will have an "effective exercise heart rate" of 120 beats/minute during roller skating. At the same time, in the process of roller skating, the muscles of the waist, hips, thighs and ankles are exerting strength. People with good skills will use reasonable swing arms to strengthen the balance of the body, improve the sliding effect, and exercise the upper limbs and even the chest muscles. So roller skating is in line with the basic elements of aerobic exercise.
Generally speaking, the maximum oxygen consumption of roller skating (the benchmark for measuring exercise intensity) is 90% of that of running, which is very effective for maintaining the optimal intensity of aerobic exercise. According to research, the heartbeat measured when skating at a speed of 23 km/h is 74% of the maximum heartbeat. It is a typical aerobic exercise, which can strengthen the cardiovascular system and burn fat. When the speed is increased to 28 km/h, the heart rate will reach 85% of the highest heart rate, improving muscle endurance. Through constant pulley movement, you should be able to adjust your body to the best condition.
Of course, from the perspective of developing cardiopulmonary endurance, roller skating is really not as good as running or brisk walking. Studies have confirmed that roller skating consumes less calories than running and has little effect on cardiopulmonary function. However, the damage of roller skating to joints is less than that of running, especially its interest and exercise effect on the flexibility of the whole body are more likely to make people interested and stick to it than running.
Because roller skating will cause the wheel to rotate when stepping on it, the elasticity of the wheel made of polyurethane has little effect on the joints, so the elderly are also engaged in this sport. Wear a helmet and protective gear, and the risk of falling injury is relatively small.
Not only that, roller skating can also cultivate people's will and enterprising spirit, which is conducive to the development of children's good psychological quality. For adults, roller skating can relieve stress, make them feel happy and relax their nerves, which has dual functions of leisure and fitness.
What are the benefits of roller skates to the body?
1. Adjusting the amount of exercise can get various exercise effects, such as losing weight and so on. -Consuming 570 to 1 150 calories per hour is similar to running. Generally speaking, the maximum oxygen consumption of roller skating (the benchmark for measuring exercise intensity) is 90% of that of running, which is very effective for maintaining the optimal intensity of aerobic exercise. According to research, the heartbeat measured when skating at a speed of 23km/h is 74% of the maximum heartbeat. It is a typical aerobic exercise, which can strengthen the cardiovascular system and burn fat. -When the speed is increased to 28km/hr, the heart rate will reach 85% of the highest heart rate and exceed the anaerobic threshold, which can improve muscle endurance. You can adjust your body to the best condition by skating constantly. 2. The risk of injury is small-because roller skating is different from running, it will cause the wheels to rotate when stepping, and the elasticity of the wheels made of polyurethane has little effect on the joints, so the elderly are also suitable for this sport-wear helmets and protective gear. The risk of injury after falling is very small. 3. It's very good exercise for growing children-improving balance, athletic ability, physical strength and endurance will help children's growth and development during their growth-more outdoor exercise with others will make their personality cheerful-the effect of burning fat will prevent the symptoms of childhood obesity. 4. Exercise with your family-from growing children to the elderly, men, women and children can enjoy the joy of exercise together-easy-to-learn exercise-and women are easy to learn. In fact, the ratio of male and female skaters is 50: 50. 5. Affordable sports-if you buy good equipment when you are a beginner, you don't have to spend any other expenses-unlike swimming, tennis and other sports, roller skating doesn't need a specific place. You don't have to spend money like a ticket-you can use it as a means of transportation according to your own strength. 6. Roller skating can make more friends-you can make more friends by participating in activities such as clubs-you can skate alone, and more people are more interested in skating together. 7. It's not easy to get bored-roller skating can be used for leisure, and diversified sports such as speed skating, street brushing, leveling, roller skating and pattern will not be easy to get bored-watching the development of your roller skating technology, you will have a great sense of accomplishment. 8. When you reach a certain technical level, you will get extra points in the college entrance examination-candidates who have won the title of national second-class athlete or above and have been tested and recognized by the provincial admissions committee in that year. On the basis of the total score of candidates' unified examination results, the score can be appropriately improved.
What are the benefits of learning roller skating?
Roller skating is a good outdoor sport.
For children, it helps to cultivate children's sense of coordination and balance and promote cerebellar development; It is conducive to strengthening physical fitness, helping children overcome their humble and closed hearts, cultivating children's independent ability and learning to live in harmony with friends.
It also has a good exercise effect on respiratory system and heart and blood system.
For adults, this is also a very leisure and interesting sport. It can not only keep fit, but also entertain and educate, broaden your horizons and make more friends. It can also be used as a means of transportation, which is very low-carbon and environmentally friendly, but pay attention to safety!
What are the benefits of playing with pulleys?
I've been playing for several years, and I don't think it's very good, but it's quite fun to play in my spare time. Playing roller skating when I am in a bad mood can also make me happy. Personally, I think roller skating is a challenging sport. I want to make friends with you!
What are the benefits of roller skating?
According to my experience:
1, he does physical exercise, can lose weight and keep fit, and consumes 570 to 1 150 calories per hour, which is equal to the effect of running.
2. Compared with running, roller skating has the least damage to the body, especially the knee joint, because it slips out and pays attention to the coordination of the whole body.
3, always keep fresh, not easy to get bored, roller skating is more fashionable and cooler. At present, South Korea should be in a leading position. If you want to go in, speed skating, street painting and leveling, you have endless skills.
4. You can find a group of like-minded friends through roller skating and open your circle of friends. This is especially important for modern teenagers, and it is much stronger than those who are addicted to the virtual world like the Internet.
5, there are many benefits, and you will have experience after practicing yourself.
What are the benefits of roller skating? What are the disadvantages?
They talked about advantages, only disadvantages. The first is adaptive bone development. The ankle valgus action of roller skating may lead to bone deformation and development, which is what we often call splayed legs, just as you see that the basic walking posture of a football player is splayed legs, and then it will affect Zhang Zi. Long-term squatting will increase the load of lower limbs and affect the local metabolic cycle. So if you look at your child's height, the suggestion is bouncing. Moreover, children generally don't know how to protect themselves when they fall, and they are prone to arm fractures. The protective gear they wear is not very effective. What I said is that these shortcomings are only possible, not that it is not good to practice roller skating. Therefore, parents should weigh the pros and cons when they let their children learn, and it is best not to be too young when they learn.