Physics - Newton's first and second law in regards to car safety
Newton's first law of motion states that: "An object in motion must stay in motion (at its present speed and direction), unless an outside force acts on it.
In regards to this law the car and its passengers are to be regarded as objects will continue moving at whatever speed the car was traveling at even if the car is stopped by a crash. Now looking at the second law, "Acceleration is produced when a force acts on a mass, the greeter the mass the greater the force needed." If the passenger were very light, he/she would have a higher probability of being thrown out of the seat than a heavier person.
Changing or stopping an object's momentum requires a force acting over it. If momentum changes suddenly, as in a car crash, the force exerted is greater. However, if the momentum gradually changes (such as when stopping for a traffic light) much less force needs to be applied with less damage or injury.
For instance in frontal collision, passenger tend to fly straight ward toward the impact, the dashboard, resulting in serious injury before getting pulled or jerked by their momentum backwards.
If the passenger is restrained by the seatbelt, their momentum is reduced by the constant and smaller force exerted by the belt.
‘Force = Mass x Acceleration’
For example, in a car crash scenario where a car stops in 1 foot from a speed of 30 mi/hr. (Assume that the driver has a mass of 160 lb.)
If the driver is firmly held in by a non-stretching seatbelt harness, then the stopping distance will be 1 ft.
If the driver is not wearing his seatbelt, the stopping distance will be determined by nature of collision with windshield, steering column, etc. : stopping distance 0.2 ft.
These calculated numbers show constant deceleration, and are therefore an estimate of the average force of impact. However, the example above proves that the amount of force exerted on the driver who is not wearing a seatbelt is significantly greater than the force exerted on a driver wearing his seatbelt.
Below please find attached images that create a car crash scenario and calculate the impact with and without a seat belt.
In regards to this law the car and its passengers are to be regarded as objects will continue moving at whatever speed the car was traveling at even if the car is stopped by a crash. Now looking at the second law, "Acceleration is produced when a force acts on a mass, the greeter the mass the greater the force needed." If the passenger were very light, he/she would have a higher probability of being thrown out of the seat than a heavier person.
Changing or stopping an object's momentum requires a force acting over it. If momentum changes suddenly, as in a car crash, the force exerted is greater. However, if the momentum gradually changes (such as when stopping for a traffic light) much less force needs to be applied with less damage or injury.
For instance in frontal collision, passenger tend to fly straight ward toward the impact, the dashboard, resulting in serious injury before getting pulled or jerked by their momentum backwards.
If the passenger is restrained by the seatbelt, their momentum is reduced by the constant and smaller force exerted by the belt.
‘Force = Mass x Acceleration’
For example, in a car crash scenario where a car stops in 1 foot from a speed of 30 mi/hr. (Assume that the driver has a mass of 160 lb.)
If the driver is firmly held in by a non-stretching seatbelt harness, then the stopping distance will be 1 ft.
- Deceleration = 967 ft/s2 = 294 m/s2 = 30 g's
- Force = 4813 lb = 21412 N = 2.4 tons
If the driver is not wearing his seatbelt, the stopping distance will be determined by nature of collision with windshield, steering column, etc. : stopping distance 0.2 ft.
- Deceleration = 4836 ft/s2 = 1474 m/s2 = 150 g's
- Force = 24068 lb = 107059 N = 12 tons
- Deceleration = 645ft/s2 = 197 m/s2 = 20 g's
- Force = 3209 lb = 14274 N = 1.6 tons
These calculated numbers show constant deceleration, and are therefore an estimate of the average force of impact. However, the example above proves that the amount of force exerted on the driver who is not wearing a seatbelt is significantly greater than the force exerted on a driver wearing his seatbelt.
Below please find attached images that create a car crash scenario and calculate the impact with and without a seat belt.
This all goes to show the great impact physics has upon car safety and accident collision.