Motorcycle Helmets and Motion Physics:
How Do Modern Motorcycle Helmets Protect Your Head?
Wearing a motorcycle helmet can help protect your head because the hard outer shell disperses the energy of an impact. The EPS foam inner padding also increases the duration of the impacting force, reducing the risk of head injury. This is how the physics of motorcycle helmets protect your head.
When you crash your bike, the severity of the damage you receive comes down to two main factors: how fast you stop and how concentrated the force is. Every motorcycle crash obeys the laws of physics.
Newton’s first law of motion states that an object in motion remains in motion. This means once the motorcycle’s travel comes to an abrupt stop, you will continue traveling at the same speed. You continue until something else stops your travel. Usually, it’s a road surface or another vehicle. Newton’s law also states that Mass X Velocity = Force. This means that a rider weighing 80 kilograms won’t hit the concrete with a force of 80 kilograms but with a far greater force. Once your head hits another object, such as a vehicle or road surface, your brain shifts violently inside your skull. Your brain is cushioned only by a very thin layer of cerebrospinal fluid. It will also follow Newton’s law until it presses up against your skull.
There is no way to break the laws of physics but you can take steps to lessen their force with the use of a motorcycle helmet.
Helmets Work in Two Ways.
A motorcycle helmet’s hard shell distributes impact energy over a greater area, reducing the pressure on any one spot. Second, the padding prolongs impact duration, reducing the peak impulse.
Without a helmet, an area of skull receiving a blow may be close to 15 or 20 square centimeters. With a helmet, the same impact force is distributed over an area of about 20% of the surface area of the helmet.
To picture the second principle at work, imagine two iPhones being dropped from a height. One hits concrete and breaks. The other hits 20 centimeters of foam and does not.
The same amount of force was required to stop both iPhones. For the iPhone that hit foam, the duration of impact was increased by a matter of milliseconds, reducing the result of that impact.
If you were to drop a 1-kilogram weight of any shape onto a person’s head from a height of 2 meters and it will probably kill them. The weight will hit their head at a speed of 10 meters per second, and because the skull is curved, it will impact an area of about 20 square centimeters.
The hard outer shell of your motorcycle helmet distributes the impact energy over the helmet surface. The inner foam in the helmet extends the impact duration, thus reducing the pressure of the impact force.
How Does Motorcycle Helmet Physics Work in Real-Life Situations?
Some people argue wearing a motorcycle helmet when traveling over a certain speed will not help in case of an accident.
A helmet will not fully protect you. In a case where you were to run head first into a brick wall head first, even at a relatively slow speed, a helmet will not fully protect your head.
When crashes occur the rider does not always experience a head impact square on with a solid obstruction. During a bike crash, your head comes in contact with the ground. The ground exerts a force that causes your head to stop moving. Often impact will be at an angle and may not be head first. It may be your shoulder will hit first, then your side, and then your head will receive a glancing blow against the ground as you slide.
The ground exerts so much force that it can stop our forward motion within seconds. Without your motorcycle helmet, your head experiences a huge amount of concentrated force during a crash.
A glancing blow has two results. Force is reduced. In scientific terms, the component of direct force is geometrically reduced.
The other result is less positive. A glancing blow creates torque, a twisting force and it can damage a spine. This is why at HelmetGeeks.com we recommend motorcycle helmets incorporating MIPS technology.
If you’re riding at 80 kph and take a spill off your bike and receive a glancing blow to the head a helmet can make all the difference in the world.
The law of conservation of energy applies in the event an opposing force stops your motion during a crash. This law states that energy can neither be created nor destroyed. When you come to an abrupt stop, your kinetic energy (the energy of our motion on your motorcycle) simply changes form. It interacts with the force the ground is exerting, and the kinetic energy becomes a part of the force that hurts us
Why Helmets Work To Protect Your Head
The hard outer shell of the helmet stops nearly instantly when it hits the ground. Your head keeps moving within the outer shell of the helmet as it stops. This is because of the padding as well as how a well-fitting helmet holds your head. Your head takes longer to stop. But the forces exerted by the helmet are smaller than they would be if you didn’t have a helmet. Because the force of the impact is distributed over the area of the helmet you are less likely to suffer a broken skull.
Motorcycle helmet shape and design play the biggest role in protection. The EPS foam in your helmet compresses on impact, which allows your head to come to a stop more slowly than it otherwise would have. This dramatically reduces your acceleration. Since force is equal to mass times acceleration, it drastically reduces the force.
The curved shape of most helmets distributes the force around its hard surface, rather than just at the point of impact.
The Laws of Physics Cannot Be Broken
Whereas the laws of physics cannot be broken, wearing a motorcycle helmet when you ride can mitigate them. Many things are strong enough to bring your motion to a complete and sudden stop in case of a crash. Helmets can take that force and minimize it by spreading the impact over your helmet surface. They also increase the time it takes your skull to stop because the foam condenses and disperses the energy. Motion always involves physics. Helmets can factor positively into the physics in play when you crash.