Bike helmets are essential for motorcycle and cycling safety, but How Does A Bike Helmet Work? At usabikers.net, we will explore the science behind helmet design, safety standards, and how helmets protect riders, ensuring you’re well-informed about this crucial piece of gear. Explore with us the mechanisms of impact absorption, rotational force reduction, and the importance of a proper fit for optimal protection, all while highlighting the vibrant community and resources available at usabikers.net.
1. Why Is Wearing a Motorcycle Helmet Important?
Wearing a motorcycle helmet is crucially important as it significantly reduces the risk of severe head injuries and fatalities in the event of an accident. Helmets provide a critical layer of protection, absorbing impact energy and minimizing trauma to the brain.
1.1 Preventing Severe Head Injuries
Motorcycle helmets are engineered to cushion the head during impact, distributing the force and reducing the likelihood of skull fractures, concussions, and traumatic brain injuries. According to the Motorcycle Safety Foundation (MSF), helmets reduce the risk of head injury by 69% and the risk of death by 37%. This protection is vital because head injuries are a leading cause of death and long-term disability in motorcycle accidents.
1.2 Legal Requirements and Standards
Many states in the USA have laws requiring motorcycle riders to wear helmets, underscoring their importance in preventing injuries and fatalities. These laws are in place because helmets have been proven to save lives and reduce the severity of injuries. Organizations like the American Motorcyclist Association (AMA) advocate for helmet use and promote awareness of safety standards. Helmets must meet specific safety standards, such as those set by the Department of Transportation (DOT), to ensure they provide adequate protection.
1.3 The Role of Proper Fit
A helmet’s effectiveness is significantly compromised if it does not fit properly. A helmet that is too loose can move during a crash, leaving parts of the head exposed, while one that is too tight can cause discomfort and may not provide sufficient impact absorption. A proper fit ensures that the helmet stays in place, covering the head completely and providing maximum protection. It should sit level on the head, with the front edge just above the eyebrows, and the chin strap should be snug but comfortable.
1.4 Encouraging Safe Riding Habits
Wearing a helmet is part of a broader culture of safe riding, which includes wearing appropriate gear, following traffic laws, and being aware of road conditions. By prioritizing safety, riders can reduce their risk of accidents and minimize the potential for serious injuries. Explore usabikers.net for more tips on safe riding practices and gear reviews to help you stay protected on the road.
2. How Does a Bike Helmet Work? The Science Behind Impact Protection
A bike helmet works through a combination of design and materials that absorb and distribute impact energy, reducing the force transmitted to the rider’s head. The primary components of a helmet include the outer shell, the impact-absorbing liner, and the retention system, each playing a critical role in protecting the rider.
2.1 The Outer Shell: Deflection and Distribution
The outer shell of a bike helmet, typically made of polycarbonate or ABS plastic, serves as the first line of defense. Its hard, smooth surface is designed to deflect objects and distribute the force of impact over a larger area. This reduces the concentration of force at any single point, preventing penetration and minimizing the risk of skull fractures. The shape and design of the shell also contribute to its ability to skid along the road surface, reducing rotational forces that can cause brain injuries.
2.2 The Impact-Absorbing Liner: Energy Absorption
The core of a bike helmet’s protective capability lies in its impact-absorbing liner, usually made of expanded polystyrene (EPS) foam. This layer is designed to crush upon impact, absorbing the energy and extending the time over which the deceleration occurs. By increasing the stopping time, the peak force transmitted to the head is significantly reduced. The thickness and density of the EPS foam are carefully calibrated to provide optimal protection without adding excessive weight or bulk to the helmet.
According to research from the Insurance Institute for Highway Safety (IIHS) in June 2024, helmets with thicker EPS liners provide better protection in high-impact crashes.
2.3 The Retention System: Secure Fit
The retention system, consisting of straps and buckles, ensures that the helmet stays securely in place during a crash. A properly fitted helmet will not shift or come off upon impact, maintaining its protective coverage. The straps should be adjusted to fit snugly under the chin, with the buckles positioned comfortably away from the ears. The retention system works in conjunction with the helmet’s internal padding to provide a secure and comfortable fit, crucial for effective protection.
2.4 Rotational Force Reduction Technologies
In addition to linear impact protection, many modern bike helmets incorporate technologies to mitigate rotational forces, which can cause serious brain injuries. Systems like MIPS (Multi-directional Impact Protection System) allow the helmet’s outer shell to rotate independently of the head during an angled impact, reducing the rotational force transmitted to the brain. These technologies represent a significant advancement in helmet design, offering enhanced protection against a wider range of crash scenarios.
2.5 Standards and Certifications
Bike helmets are subject to rigorous testing and certification standards to ensure their protective performance. Organizations like the Department of Transportation (DOT) set minimum safety requirements for helmets sold in the USA. Helmets that meet these standards are marked with a DOT sticker, indicating that they have been tested and certified to provide adequate protection. Riders should always choose helmets that meet or exceed these standards to ensure they are getting the best possible protection.
3. What Are the Key Components of a Motorcycle Helmet?
The key components of a motorcycle helmet include the outer shell, impact-absorbing liner, comfort padding, retention system, and visor, each contributing to the helmet’s overall safety and functionality. Understanding these components helps riders appreciate the engineering behind helmet design and make informed choices when selecting a helmet.
3.1 Outer Shell
The outer shell of a motorcycle helmet provides the first line of defense against impacts, deflecting objects and distributing force over a larger area. It is typically made from materials like polycarbonate, fiberglass, or carbon fiber, each offering different levels of strength, weight, and impact resistance. A high-quality outer shell is crucial for preventing penetration and minimizing the risk of skull fractures.
3.2 Impact-Absorbing Liner
The impact-absorbing liner, usually made of expanded polystyrene (EPS) foam, is designed to crush upon impact, absorbing energy and extending the deceleration time. This layer is critical for reducing the peak force transmitted to the head, preventing serious brain injuries. The thickness and density of the EPS liner are carefully calibrated to provide optimal protection without adding excessive weight or bulk.
3.3 Comfort Padding
Comfort padding lines the interior of the helmet, providing a comfortable and secure fit. It is typically made from soft, moisture-wicking materials that help to absorb sweat and keep the rider cool and dry. The padding is often removable and washable, allowing riders to maintain hygiene and prolong the life of their helmet.
3.4 Retention System
The retention system consists of straps and buckles that secure the helmet to the rider’s head. It is essential that the retention system is properly adjusted to ensure a snug and comfortable fit, preventing the helmet from shifting or coming off during a crash. The straps should be made from durable materials and the buckles should be easy to use, even with gloves on.
3.5 Visor
The visor protects the rider’s eyes from wind, dust, debris, and sunlight. It is typically made from scratch-resistant and shatterproof materials, providing clear visibility in a variety of riding conditions. Some helmets feature adjustable or retractable visors, allowing riders to customize their protection based on the environment.
3.6 Additional Features
Modern motorcycle helmets often include additional features such as ventilation systems, communication systems, and emergency quick-release systems. Ventilation systems provide airflow to keep the rider cool and comfortable, while communication systems allow for hands-free communication with other riders or devices. Emergency quick-release systems enable first responders to safely remove the helmet in the event of an accident, minimizing the risk of further injury.
4. How Do Different Types of Helmets Offer Varied Protection?
Different types of helmets, including full-face, modular, open-face, and half helmets, offer varied levels of protection based on their design and coverage. Understanding these differences is essential for choosing the right helmet for your riding style and safety needs.
4.1 Full-Face Helmets: Maximum Coverage
Full-face helmets provide the highest level of protection, covering the entire head and face. They feature a chin bar that protects the jaw and face from impacts, as well as a visor that shields the eyes from wind, dust, and debris. Full-face helmets are recommended for all types of riding, especially high-speed and long-distance riding, where maximum protection is essential.
4.2 Modular Helmets: Versatility and Convenience
Modular helmets, also known as flip-up helmets, offer a combination of full-face protection and open-face convenience. They feature a hinged chin bar that can be raised to allow the rider to talk, eat, or take a break without removing the helmet. While modular helmets offer good protection, they may not be as strong as full-face helmets due to the hinged design.
4.3 Open-Face Helmets: Partial Coverage
Open-face helmets, also known as three-quarter helmets, cover the top, back, and sides of the head, but leave the face exposed. They offer less protection than full-face or modular helmets, as they do not have a chin bar to protect the jaw and face. Open-face helmets are often preferred by riders who want a greater sense of freedom and airflow, but they should be used with caution and are not recommended for high-speed riding.
4.4 Half Helmets: Minimal Protection
Half helmets, also known as skull caps, provide minimal coverage, typically only covering the top of the head. They offer very little protection in the event of a crash and are not recommended for serious riding. Half helmets may be popular for their minimalist style, but they should be avoided by riders who prioritize safety.
4.5 Choosing the Right Helmet
When choosing a motorcycle helmet, it is essential to consider your riding style, safety needs, and personal preferences. Full-face helmets offer the best overall protection, while modular helmets provide a balance of protection and convenience. Open-face and half helmets offer less protection and are not recommended for high-speed riding. Always choose a helmet that fits properly, meets safety standards, and provides the level of protection you need to ride with confidence.
4.6 Resources at usabikers.net
For more detailed information on different helmet types and recommendations, visit usabikers.net. Our website offers a wealth of resources, including helmet reviews, safety tips, and community forums where you can connect with experienced riders and get personalized advice.
5. What Are the Standards and Certifications for Bike Helmets?
Bike helmets are subject to various standards and certifications, including DOT, Snell, and ECE, ensuring they meet minimum safety requirements and provide adequate protection. Understanding these standards helps riders choose helmets that have been rigorously tested and certified for safety.
5.1 Department of Transportation (DOT)
The Department of Transportation (DOT) sets the minimum safety standards for motorcycle helmets sold in the USA. DOT-certified helmets must meet specific requirements for impact resistance, penetration resistance, and retention system strength. Helmets that meet these standards are marked with a DOT sticker on the back.
5.2 Snell Memorial Foundation (Snell)
The Snell Memorial Foundation is a non-profit organization that conducts independent testing and certification of motorcycle helmets. Snell standards are more rigorous than DOT standards, requiring helmets to withstand higher impact forces and provide greater coverage. Helmets that meet Snell standards are marked with a Snell sticker.
5.3 Economic Commission for Europe (ECE)
The Economic Commission for Europe (ECE) sets safety standards for motorcycle helmets sold in Europe. ECE-certified helmets must meet specific requirements for impact resistance, penetration resistance, retention system strength, and field of vision. ECE standards are widely recognized and accepted around the world.
5.4 How to Check for Certifications
When purchasing a motorcycle helmet, always look for the DOT, Snell, or ECE sticker to ensure that the helmet meets safety standards. The sticker should be located on the back of the helmet and should be clearly visible. You can also check the helmet manufacturer’s website for information on certifications and testing.
5.5 The Importance of Compliance
Choosing a helmet that meets safety standards is crucial for protecting yourself in the event of a crash. Non-certified helmets may not provide adequate protection and could increase your risk of serious injury or death. Always prioritize safety when selecting a motorcycle helmet and choose a helmet that has been rigorously tested and certified for safety.
5.6 Resources at usabikers.net
For more information on helmet standards and certifications, visit usabikers.net. Our website offers comprehensive guides, reviews, and resources to help you make informed decisions about your motorcycle gear. Join our community forums to discuss helmet safety with experienced riders and get personalized recommendations.
6. How Does a Bike Helmet Absorb Impact?
A bike helmet absorbs impact through a combination of materials and design features that work together to reduce the force transmitted to the head. The key components involved in impact absorption include the outer shell, the impact-absorbing liner, and the distribution of force across the helmet’s structure.
6.1 Crushing and Compression
The primary mechanism by which a bike helmet absorbs impact is through the crushing and compression of the impact-absorbing liner. This liner, typically made of expanded polystyrene (EPS) foam, is designed to deform and crush upon impact, converting kinetic energy into heat and mechanical deformation. By crushing, the liner extends the time over which the deceleration occurs, reducing the peak force transmitted to the head.
6.2 Force Distribution
The outer shell of a bike helmet plays a crucial role in distributing the force of impact over a larger area. By spreading the force, the shell reduces the concentration of stress at any single point, preventing penetration and minimizing the risk of skull fractures. The shape and design of the shell also contribute to its ability to skid along the road surface, reducing rotational forces that can cause brain injuries.
6.3 Material Properties
The materials used in bike helmets are carefully selected for their impact-absorbing properties. EPS foam is lightweight, cost-effective, and highly effective at absorbing energy through crushing. Other materials, such as polycarbonate and ABS plastic, are used for the outer shell due to their strength, durability, and ability to distribute force.
6.4 Multi-Density Liners
Some advanced bike helmets feature multi-density liners, which use different densities of EPS foam in different areas of the helmet to optimize impact absorption. Softer foam is used in areas that are more likely to experience low-impact collisions, while denser foam is used in areas that need to withstand high-impact forces. This multi-density approach allows for a more customized and effective level of protection.
6.5 Testing and Validation
Bike helmets are subject to rigorous testing and validation to ensure their impact-absorbing capabilities. Standards organizations like DOT, Snell, and ECE conduct impact tests on helmets to measure their ability to reduce the force transmitted to the head. These tests involve dropping helmets onto various anvils at different speeds and measuring the resulting acceleration. Helmets that pass these tests are certified to meet safety standards.
6.6 Additional Insights
For more in-depth information on how bike helmets absorb impact, visit usabikers.net. Our articles and guides provide detailed explanations of helmet technology, materials, and testing procedures. Join our community forums to discuss helmet safety with experts and fellow riders.
7. How Do Rotational Forces Affect the Brain, and How Do Helmets Mitigate Them?
Rotational forces can significantly affect the brain during a crash, leading to serious injuries, and helmets with advanced technologies are designed to mitigate these forces. Understanding how rotational forces impact the brain and how helmets address this risk is crucial for rider safety.
7.1 The Impact of Rotational Forces on the Brain
When the head is subjected to rotational forces during a crash, the brain can twist and stretch within the skull, leading to diffuse axonal injury (DAI). DAI occurs when nerve cells in the brain are damaged due to the twisting and stretching, resulting in cognitive impairment, loss of consciousness, and other neurological problems. Rotational forces are a significant factor in many motorcycle accidents and can cause serious long-term damage.
7.2 MIPS (Multi-directional Impact Protection System)
MIPS is a technology designed to reduce rotational forces by allowing the helmet’s outer shell to rotate independently of the head during an angled impact. This rotation reduces the amount of force transmitted to the brain, minimizing the risk of DAI. MIPS consists of a low-friction layer between the helmet’s outer shell and liner, which allows the helmet to slide relative to the head.
7.3 Other Rotational Force Reduction Technologies
In addition to MIPS, other technologies are available to reduce rotational forces. These include:
- WaveCel: WaveCel is a collapsible cellular structure that lines the inside of the helmet. It is designed to flex, crumple, and glide upon impact, reducing rotational forces and linear impact forces.
- SPIN (Shearing Pad INside): SPIN is a silicone pad technology developed by POC that is designed to shear during an angled impact, reducing rotational forces.
- Torque Redirecting System (TRS): TRS is a technology used in some Klim helmets that consists of energy-absorbing dampers that help to reduce rotational forces.
7.4 Testing and Validation of Rotational Force Reduction
The effectiveness of rotational force reduction technologies is evaluated through testing and validation. Some standards organizations, such as Virginia Tech, conduct independent testing of helmets to measure their ability to reduce rotational forces. These tests involve subjecting helmets to angled impacts and measuring the resulting rotational acceleration.
7.5 Choosing a Helmet with Rotational Force Reduction
When selecting a motorcycle helmet, consider choosing one with rotational force reduction technology. Look for helmets that feature MIPS, WaveCel, SPIN, or other similar technologies. These helmets offer enhanced protection against rotational forces and can reduce your risk of serious brain injury.
7.6 Explore More at usabikers.net
To learn more about rotational forces and helmet technologies, visit usabikers.net. Our website provides detailed articles, reviews, and resources on helmet safety. Join our community forums to discuss helmet technology with experts and fellow riders, and stay informed about the latest advancements in helmet safety.
8. What is the Lifespan of a Bike Helmet, and How Do You Know When to Replace It?
The lifespan of a bike helmet is typically three to five years, but it should be replaced sooner if it has been involved in a crash or shows signs of damage. Knowing when to replace your helmet is crucial for maintaining its protective capabilities.
8.1 General Guidelines for Replacement
Bike helmets should be replaced every three to five years, regardless of their appearance or usage. Over time, the materials in the helmet can degrade due to exposure to sunlight, heat, and sweat, reducing their ability to absorb impact energy. Even if the helmet looks fine, its protective capabilities may be compromised.
8.2 Replacement After a Crash
If a bike helmet has been involved in a crash, it should be replaced immediately, even if there is no visible damage. The impact-absorbing liner may have been compressed during the crash, reducing its ability to protect your head in a future impact. Do not continue using a helmet that has been involved in a crash.
8.3 Signs of Damage
Inspect your bike helmet regularly for signs of damage, such as cracks, dents, or discoloration. Cracks in the outer shell or compression of the EPS liner indicate that the helmet’s structural integrity has been compromised. Discoloration can indicate that the materials have degraded due to UV exposure. If you notice any of these signs of damage, replace your helmet immediately.
8.4 Proper Storage
Proper storage can prolong the lifespan of your bike helmet. Store your helmet in a cool, dry place away from direct sunlight and heat. Avoid storing your helmet in a garage or car, where temperatures can fluctuate and cause the materials to degrade. Clean your helmet regularly with mild soap and water, and avoid using harsh chemicals or solvents.
8.5 Manufacturer Recommendations
Check the manufacturer’s recommendations for the lifespan of your bike helmet. Some manufacturers provide specific guidelines for replacement based on the materials used and the intended usage. Follow these recommendations to ensure that your helmet provides adequate protection.
8.6 Staying Informed with usabikers.net
For more information on helmet lifespan and maintenance, visit usabikers.net. Our articles and guides provide detailed advice on how to care for your helmet and when to replace it. Join our community forums to discuss helmet maintenance with experienced riders and get personalized recommendations.
9. How to Ensure a Bike Helmet Fits Properly?
Ensuring a bike helmet fits properly is crucial for its effectiveness in protecting your head during a crash. A properly fitted helmet will stay in place, provide adequate coverage, and absorb impact energy effectively.
9.1 Measuring Your Head
Start by measuring your head circumference. Use a flexible measuring tape to measure around the largest part of your head, about one inch above your eyebrows. Note the measurement in centimeters or inches, and use this measurement to select the correct helmet size.
9.2 Trying On the Helmet
When trying on a bike helmet, make sure it sits level on your head, with the front edge about one inch above your eyebrows. The helmet should fit snugly, but not too tightly, and should not move around when you shake your head. If the helmet is too loose or too tight, try a different size.
9.3 Adjusting the Fit
Most bike helmets have adjustable straps and padding that allow you to customize the fit. Adjust the straps so that they form a “V” shape around your ears, and the buckle sits comfortably under your chin. The straps should be snug, but not too tight, and should not rub against your ears. Use the adjustable padding to fine-tune the fit and ensure that the helmet is comfortable and secure.
9.4 The “Eyebrow Test”
Perform the “eyebrow test” to check the fit of the helmet. With the helmet on and the straps buckled, try to push the helmet up and off your head from the front. If you can push the helmet up far enough to expose your forehead, the helmet is too loose and needs to be adjusted or replaced.
9.5 The “Shake Test”
Perform the “shake test” to check the fit of the helmet. With the helmet on and the straps buckled, shake your head from side to side and up and down. The helmet should stay in place and should not move around on your head. If the helmet moves around, it is too loose and needs to be adjusted or replaced.
9.6 Seeking Professional Advice
If you are unsure about the fit of your bike helmet, seek professional advice from a qualified helmet fitter. Many bike shops and motorcycle dealerships offer helmet fitting services and can help you find a helmet that fits properly and provides adequate protection.
9.7 More Tips at usabikers.net
For more detailed information on how to ensure a bike helmet fits properly, visit usabikers.net. Our articles and guides provide step-by-step instructions and helpful tips for finding the perfect fit. Join our community forums to discuss helmet fitting with experienced riders and get personalized recommendations.
Proper Motorcycle Helmet Fit
10. What Are Some Common Misconceptions About Bike Helmets?
There are several common misconceptions about bike helmets, including the belief that all helmets offer the same level of protection and that helmets are unnecessary for low-speed riding. Addressing these misconceptions is essential for promoting safe riding practices.
10.1 Misconception: All Helmets Offer the Same Level of Protection
Not all bike helmets offer the same level of protection. Helmets vary in terms of their design, materials, and certification. Helmets that meet higher safety standards, such as Snell or ECE, offer greater protection than helmets that only meet the minimum DOT standards. Always choose a helmet that meets recognized safety standards and is appropriate for your riding style and conditions.
10.2 Misconception: Helmets Are Unnecessary for Low-Speed Riding
Helmets are necessary for all types of riding, including low-speed riding. Even at low speeds, a crash can result in serious head injuries. Many accidents occur at intersections or in parking lots, where speeds may be low, but the risk of impact with other vehicles or objects is still present. Always wear a helmet, regardless of the speed or distance of your ride.
10.3 Misconception: Helmets Can Prevent All Head Injuries
While helmets can significantly reduce the risk of head injuries, they cannot prevent all injuries in all situations. The severity of a crash and the nature of the impact can exceed the protective capabilities of a helmet. However, wearing a helmet still provides a critical layer of protection and can reduce the severity of head injuries in most crashes.
10.4 Misconception: Helmets Are Only Necessary for Experienced Riders
Helmets are necessary for all riders, regardless of their experience level. Inexperienced riders may be more prone to accidents due to their lack of skill and judgment. Wearing a helmet can help protect inexperienced riders from serious head injuries while they are learning to ride.
10.5 Misconception: Helmets Are Uncomfortable and Inconvenient
Modern bike helmets are designed to be comfortable and convenient to wear. They feature lightweight materials, adjustable straps and padding, and ventilation systems that keep you cool and comfortable. While some riders may find helmets to be slightly inconvenient, the benefits of wearing a helmet far outweigh any minor discomfort or inconvenience.
10.6 Stay Informed with usabikers.net
To learn more about bike helmet safety and dispel common misconceptions, visit usabikers.net. Our website provides informative articles, guides, and resources on helmet technology, safety standards, and proper usage. Join our community forums to discuss helmet safety with experienced riders and get personalized advice.
At usabikers.net, we are dedicated to providing you with the most current and reliable information to help you make informed decisions about your safety. We encourage you to explore our resources, engage with our community, and prioritize safety on every ride. Remember, wearing a helmet is a simple yet effective way to protect yourself and enjoy the freedom of the open road. Contact us at 801 Sturgis Main St, Sturgis, SD 57785, United States, or call +1 (605) 347-2000. Visit our website usabikers.net to learn more.
FAQ: Bike Helmets
1. How does a bike helmet work to protect my head?
A bike helmet works by absorbing and distributing the impact energy during a crash. The outer shell deflects objects and spreads the force, while the EPS foam liner crushes to absorb energy, reducing the force transmitted to your head.
2. What are the different types of bike helmets available?
The different types of bike helmets include full-face, modular, open-face, and half helmets. Full-face helmets offer the most protection, while half helmets offer the least.
3. How do I choose the right size bike helmet?
To choose the right size bike helmet, measure your head circumference and consult the manufacturer’s sizing chart. The helmet should fit snugly and sit level on your head, about one inch above your eyebrows.
4. What safety standards should I look for when buying a bike helmet?
When buying a bike helmet, look for helmets that meet DOT, Snell, or ECE safety standards. These standards ensure that the helmet has been tested and certified to provide adequate protection.
5. How often should I replace my bike helmet?
You should replace your bike helmet every three to five years, or immediately after a crash, even if there is no visible damage.
6. Can a bike helmet prevent all head injuries?
While bike helmets can significantly reduce the risk of head injuries, they cannot prevent all injuries in all situations. The severity of the crash and the nature of the impact can exceed the protective capabilities of a helmet.
7. How do rotational forces affect the brain, and how do helmets mitigate them?
Rotational forces can cause the brain to twist and stretch within the skull, leading to diffuse axonal injury (DAI). Helmets with MIPS or other rotational force reduction technologies can help mitigate these forces by allowing the helmet to rotate independently of the head during an angled impact.
8. Are expensive bike helmets safer than cheaper ones?
Expensive bike helmets are not necessarily safer than cheaper ones, as long as they meet the same safety standards. However, more expensive helmets may offer additional features, such as better ventilation, comfort, and rotational force reduction technologies.
9. How should I store my bike helmet when not in use?
Store your bike helmet in a cool, dry place away from direct sunlight and heat. Avoid storing your helmet in a garage or car, where temperatures can fluctuate and cause the materials to degrade.
10. Where can I find more information about bike helmet safety?
You can find more information about bike helmet safety at usabikers.net. Our website provides informative articles, guides, and resources on helmet technology, safety standards, and proper usage.
